APMP Supplementary Comparisons of LED Measurements€¦ · APMP Supplementary Comparisons of LED...

APMP Supplementary Comparisons of

LED Measurements

APMP.PR-S3a Averaged LED Intensity

APMP.PR-S3b Total Luminous Flux of LEDs

APMP.PR-S3c Emitted Colour of LEDs

Final Report (July 2012)

Dong-Hoon Lee, Seongchong Park, and Seung-Nam Park

Division of Physical Metrology, Korea Research Institute of Standards and Science (KRISS)

267 Gajeong-Ro, Yuseong-Gu, Daejeon 305-340, Rep. Korea

Correspondance to: [email protected]

APMP.PR-S3a Averaged LED Intensity Final Report

2

Table of Contents

1. Introduction ...................................................................................................................................................... 5

2. Comparison Protocol .................................................................................................................................... 5

3. Artifact LEDs ..................................................................................................................................................... 7

4. Measurement Capabilities of Participants........................................................................................... 9

4.1. KRISS .......................................................................................................................................................... 9

4.2. MIKES ...................................................................................................................................................... 14

4.3. CMS-ITRI ................................................................................................................................................ 22

4.4. PTB ........................................................................................................................................................... 29

4.5. NMIJ ......................................................................................................................................................... 37

4.6. CENAM ................................................................................................................................................... 44

4.7. LNE ........................................................................................................................................................... 52

4.8. METAS ..................................................................................................................................................... 63

4.9. NMC-A*STAR ....................................................................................................................................... 74

4.10. VSL ....................................................................................................................................................... 80

4.11. NMIA ................................................................................................................................................... 89

4.12. NIST ..................................................................................................................................................... 98

4.13. VNIIOFI ............................................................................................................................................. 104

4.14. MKEH ................................................................................................................................................ 104

4.15. INM .................................................................................................................................................... 109

5. Reported Results of Participants ........................................................................................................ 117

5.1. KRISS ..................................................................................................................................................... 117

5.2. MIKES .................................................................................................................................................... 120

5.3. CMS-ITRI .............................................................................................................................................. 120

5.4. PTB ......................................................................................................................................................... 121

5.5. NMIJ ....................................................................................................................................................... 121


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5.6. CENAM ................................................................................................................................................. 122

5.7. LNE ......................................................................................................................................................... 122

5.8. METAS ................................................................................................................................................... 123

5.9. NMC-A*STAR ..................................................................................................................................... 123

5.10. VSL ..................................................................................................................................................... 124

5.11. NMIA ................................................................................................................................................. 125

5.12. NIST ................................................................................................................................................... 125

5.13. VNIIOFI ............................................................................................................................................. 126

5.14. MKEH ................................................................................................................................................ 126

5.15. INM .................................................................................................................................................... 127

6. Pre-draft A Process .................................................................................................................................. 128

6.1. Verification of Reported Results ............................................................................................... 128

6.2. Temperature Correction and Artifact Drift ........................................................................... 128

6.3. Review of Relative Data ................................................................................................................ 137

6.4. Review of Uncertainty Budgets ................................................................................................. 138

6.5. Identification of Outliers ............................................................................................................... 138

7. Data Analysis ............................................................................................................................................... 139

7.1. Calculation of Difference to Pilot ............................................................................................. 139

7.2. Calculation of Comparison Reference Value ....................................................................... 140

7.3. Calculation of Degree of Equivalence .................................................................................... 141

7.4. Data Analysis Spreadsheet .......................................................................................................... 141

8. Comparison Results ................................................................................................................................. 142

8.1. Red LEDs .............................................................................................................................................. 142

8.2. Green LEDs ......................................................................................................................................... 144

8.3. Blue LEDs ............................................................................................................................................. 146

8.4. White LEDs.......................................................................................................................................... 148


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8.5. Diffuser-type Green LEDs ............................................................................................................. 150

9. Discussion ..................................................................................................................................................... 153

9.1. Test of Consistency ......................................................................................................................... 153

9.2. Accuracy of Alignment .................................................................................................................. 153

9.3. Accuracy of Color Correction ..................................................................................................... 154

10. Summary .................................................................................................................................................. 157

Acknowledgement ............................................................................................................................................. 158

Appendix A: Technical Protocol ................................................................................................................... 159

Appendix B: Review of Relative Data ........................................................................................................ 160

Appendix C: Comments from Review of Relative Data .................................................................... 161

Appendix D: Comments from Review of Uncertainty Budgets ..................................................... 162

Appendix E: Identification of Outliers ....................................................................................................... 163

Appendix F: Comments and Revision to Draft A Report ................................................................. 164


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1. Introduction

With the recent growth of the solid state lighting and display industry, the interest and

importance of accurate measurement of light-emitting diodes (LEDs) are increasing.

Photometric measurement of LEDs, however, is influenced by the specific properties of

individual LED such as spectral distribution, spatial emission profile, temperature

dependence, etc. In general, the measurement uncertainty of LEDs is larger than that of

the conventional incandescent lamps, and greater care is required to avoid or correct the

systematic errors related to the LED properties.

The Asia Pacific Metrology Programme (APMP) Technical Committee of Photometry

and Radiometry (TCPR) decided at its meeting in December 2006 to conduct

supplementary comparisons on measurement of LEDs to test the metrological

equivalence among national metrology institutes (NMIs) under the CIPM Mutual

Recognition Arrangement (MRA)1. The participation was not limited to NMIs in APMP, but

also NMIs of other regional metrology organizations (RMOs). The Korea Research

Institute of Standards and Science (KRISS) of Republic Korea is designated as the pilot

laboratory.

Three measurement quantities of LEDs are selected for the comparisons, which are

listed as service categories for Calibration and Measurement Capabilities (CMCs):

averaged LED intensity in condition B defined by International Commission on

Illumination (CIE) 2 , total luminous flux, and emitted color expressed as chromaticity

coordinates (x, y) according to the CIE 1931 standard colorimetric system3. The three

comparisons are registered as APMP.PR-S3a, -S3b, and -S3c, respectively.

In this report, we summarize the results of the comparison S3a on averaged LED

intensity.

2. Comparison Protocol

The organization, the artifact LEDs, and the guidelines for measurement and report of all

the three comparisons (S3a, S3b, S3c) are settled on one technical protocol before the

start of the comparisons. The protocol is drafted by the pilot lab, agreed by the

participants, and approved by the APMP TCPR in January 2008. The protocol is once

revised in November 2008, as the INM of Romania has joined as an additional participant.

1 http://www.bipm.org/en/cipm-mra/ 2 Measurement of LEDs, 2nd edition, CIE Technical Report 127-2007. 3 Colorimetry, 3rd edition, CIE 015:2004.


6

The final version of the technical protocol is included in

Table 10-1. Summary of the unilateral DoEs and their uncertainties for APMP.PR-S3a (temperature correction applied).

NMI

RED GREEN BLUE WHITE DIFFUSE

DoE U of

DoE DoE

U of

DoE DoE

U of

DoE DoE

U of

DoE DoE

U of

DoE

MIKES -0.001 0.039 0.002 0.040 0.021 0.042 0.005 0.037 0.002 0.020

CMS-ITRI -0.022 0.049 -0.012 0.044 -0.014 0.050 -0.019 0.043 -0.011 0.045

PTB 0.003 0.034 0.001 0.026 -0.004 0.037 0.002 0.024 -0.007 0.020

NMIJ -0.021 0.032 0.019 0.035 0.045 0.044 0.001 0.037 0.011 0.027

CENAM -0.343 0.062 -0.126 0.072 -0.076 0.068 -0.201 0.060 -0.147 0.069

LNE 0.020 0.032 0.030 0.027 0.008 0.035 0.010 0.050 0.030 0.022

METAS -0.028 0.028 -0.001 0.026 0.025 0.039 -0.015 0.020 -0.010 0.025

NMC-

A*STAR 0.007 0.029 -0.002 0.027 0.014 0.029 -0.008 0.023 -0.008 0.024

VSL 0.006 0.026 0.013 0.028 0.010 0.029 0.004 0.030 0.004 0.027

NMIA 0.101 0.043 -0.063 0.030 -0.035 0.031 0.035 0.021 -0.008 0.023

NIST 0.031 0.034 0.036 0.032 0.032 0.044 0.033 0.027 0.041 0.025

VNIIOFI 0.037 0.021 -0.033 0.034 -0.085 0.028 -0.010 0.017 -0.029 0.025

MKEH -0.022 0.024 0.026 0.024 0.067 0.032 0.004 0.022 0.015 0.018

INM 0.082 0.116 0.118 0.114 0.123 0.131 0.093 0.112 0.164 0.114

KRISS -0.011 0.018 -0.012 0.017 0.000 0.018 -0.019 0.015 -0.021 0.015

Acknowledgement

The pilot work of this comparison is partly supported by the Korean Ministry of

Knowledge and Economy under the project of LED standardization, grant B0010209.


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Appendix A: Technical Protocol as an electronic file. Table 0-1 shows the final list of

participants to the S3a comparison with the measurement schedules planned and

performed. We note that the NPL of the UK listed on the technical protocol has

withdrawn its participation in August 2009.

Table 0-1. List of participants and measurement schedules of APMP.PR-S3a.

NMI country contact person(s) measurement

planned LED set

measurement

performed

results

reported

KRISS

(pilot) Korea

Seongchong Park,

Dong-Hoon Lee -- -- -- --

NMC-

A*STAR

Singapore Yuanjie Liu,

Gan Xu

June ~ Aug.

2008 #8

10 July ~ 28 Aug.

2008

12 Jan.

2009

MIKES Finland (Pasi Manninen),

Tuomas Poikonen,

March ~ May

2008 #1

7 April ~ 13 April

2008

17 June

2008

NIST USA

Cameron Miller,

Yoshi Ohno,

Yuqin Zong

Aug. ~ Oct.

2008 #3

18 Feb. ~ 25 Feb.

2009

31 July

2009

CMS-

ITRI

Chinese

Taipei Cheng-Hsien Chen

March ~ May

2008 #2

26 May 2008 ~ 2

Oct. 2009*

26 Oct

2009

PTB Germany

Matthias

Lindemann,

Robert Maass

April ~ June

2008 #3 May ~ July 2008

18 July

2009

CENAM Mexico

Laura P. González,

Anayansi Estrada,

Eric Rosas

May ~ July

2008 #5

17 July ~ 21 July

2008

08 May

2009

NMIJ Japan Kenji Godo,

(Terubumi Saito)

April ~ June

2008 #4

17 April ~ 22

June 2008

01 Aug.

2008

METAS Switzerland Peter Blattner June ~ Aug.

2008 #7

08 Sept ~ 17 Sept

2008

07 April

2009

LNE France Jimmy Dubard May ~ July

2008 #6

15 June ~ 13 July

2008

15 April

2009

VSL The

Netherlands

(Eric van der Ham),

M. Charl Moolman,

Daniel Bos

July ~ Sept.

2008 #1

13 Oct 2008 ~ 12

Jan 2009

1 Oct

2009

NMIA Australia (Philip Lukins),

Peter Manson

July ~ Sept.

2008 #2 Jan. ~ May 2009

4 May

2010

VNIIOFI Russia Tatiana Gorshkova,

Stanislav Shirokov

Sept. ~ Nov.

2008 #5

28 Nov ~ 05 Dec

2008

06 Feb.

2009

MKEH Hungary George Andor Sept. ~ Nov.

2008 #6

20 Nov ~ 09 Dec

2008

25 March

2009

INM Romania Mihai Simionescu Nov. ~ Dec.

2008 #7 Dec 2008

30 March

2009

* The CMS-ITRI had the initial measurement in May 2008, but it had to repeat the measurement on the red

LEDs in Oct 2009 due to damages in the initial measurement.

The comparison was performed as a star-type circulation of multiple sets of artifact

LEDs. The round for each participant had the following sequence: (1) first measurement

by the pilot, (2) measurement by the participant, (3) second measurement by the pilot.

The results of the repeated measurement by the pilot are used to evaluate the stability of


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the artifact LEDs.

3. Artifact LEDs

Five different types of LEDs are used as comparison artifacts: RED (Nichia model

NSPR518S), GREEN (Nichia model NSPG518S), BLUE (Nichia model NSPB518S), WHITE

(Nichia model NSPW515BS), and DIFFUSER-TYPE GREEN (NSPG518S mounted in a

cylinder-type cap with an opal diffuser). All the bare LEDs had a lamp diameter of 5 mm

and were to be operated at a forward direct current of 20 mA. The detailed information

of the LEDs is included in the technical protocol (Appendix A).

Each set of artifact LEDs consisted of three pieces of the red (R), green (G), blue (B),

and white (W) LEDs and two pieces of the diffuser-type green (D) LEDs. They were

packaged and identified as shown in Fig. 3-1. The pilot prepared eight sets of artifact

LEDs for the LED comparisons S3a, S3b, and S3c. Each artifact LED is designated in a

form #N-X-M with three codes:

- #N as the artifact set number: N = 1, 2, …, 8

- X as LED color and type code: X = R for red, G for green, B for blue, W for white, D for

diffuser-type green

- M as sample serial number for each type: M = 1, 2, 3

Fig. 3-1. Artifact LED set circulated in the LED comparisons S3a, S3b, and S3c.

The artifact LEDs are prepared based on the functional seasoning 4 that records

4 Seongchong Park et al., Metrologia 43, 299 (2006).


9

during the pre-burning the relative change of luminous intensity and spectral distribution

of each individual LED together with its junction voltage under the ambient temperature

periodically varied from 18 °C to 33 °C. From the recorded data, the temporal drift and

the temperature dependence of the optical characteristics of each LED could be

separately determined. Each artifact LEDs has passed a seasoning procedure over 300

hours.

Since the photometric properties of LEDs have a very high dependence upon

temperature, their comparison requires a sensitive control or monitoring of the junction

temperature. As the junction voltage Vj of a LED can be approximated as a linear

function of the junction temperature T in a small interval, say ±10 °C, around a reference

temperature of T0,5 we can model the temperature dependence of the averaged LED

intensity ILED as a third-order polynomial with three coefficients:

2 3

0 0 0

0

1 ( ) ( ) ( ) ( ) ( ) ( )LED

j j j j j j

LED

I Ta V T V T b V T V T c V T V T

I T . (3-1)

The coefficients a, b, and c of each artifact LED could be determined by fitting the

function of Eq. (3-1) to the functional seasoning data. With these results, the pilot was

capable to calculate a temperature correction factor for the measurement result of any

artifact LED to the same measurement condition, as long as the junction voltage at the

time of measurement is known. The uncertainty of this correction factor is estimated to

be less than 0.5 % as a relative standard uncertainty from the goodness of fit for the

coefficients.

In the comparison S3a, the measurement condition was specified with an ambient

temperature of 25 °C. In addition, the junction voltage of each LED was to be recorded

to monitor the junction temperature and to apply the aforementioned temperature

correction. In the chapters 0~0, we will show and discuss this effect of the temperature

correction to the comparison results.

5 See, for example, E. F. Schubert, Light-Emitting Diodes (Cambrige University Press, 2003)


10

4. Measurement Capabilities of Participants

In this chapter, we summarize the information on measurement capabilities and

uncertainty budgets for averaged LED intensity, which are reported by each participant.

4.1. KRISS

4.1.1. Measurement setup

Fig. 4-1 shows the measurement setup of the averaged LED intensity. The main detector

is an illuminance meter with a circular aperture of 1 cm2 (P15F0T made by LMT). For

spectral mismatch correction and color measurement, we use a CCD-mounted

spectrograph-type spectroradiometer (CAS140CT-153 made by Instrument Systems), of

which the input optics is composed of a 1.5-inch integrating sphere and fiber bundle.

The aperture area of the integrating sphere is 1 cm2. It covers 380 nm to 1050 nm, and

its spectral bandwidth (FWHM) is about 3 nm at 633 nm. The detector holder is mounted

on a 5-axis stage.

The LED is driven by a source-meter unit (2400 source-meter made by Keithley),

which provides both of current sourcing and voltage measuring function. The DUT LED is

connected to the source-meter unit using 4-wire connection. As shown in Fig. 4-1 and

Fig. 4-2, the LED socket is cone-shaped and mounted on a 5-axis stage, which provides

4-wire electrical contacts to the LED.

Fig. 4-1. Averaged LED intensity measurement setup in KRISS.

illuminance meter

: 1 cm2 aperture

input optics of

spectroradiometer

: 1 cm2 aperture

telescope

for axis alignment

telescope

for distance alignment

baffle

detector

mountLED socket

detectors5-axis stage 5-axis stage

illuminance meter

: 1 cm2 aperture

input optics of

spectroradiometer

: 1 cm2 aperture

telescope

for axis alignment

telescope

for distance alignment

baffle

detector

mountLED socket

detectors5-axis stage 5-axis stage


11

Fig. 4-2. LED Measurement socket in KRISS.

4.1.2. Mounting and alignment

As shown in Fig. 4-1, there are two 5-axis stages and two telescope cameras. Using an

alignment laser and a couple of centering jigs (made of a precision reticule), the axis of

the optical bench is aligned, and successively the cameras position and tilt are adjusted.

One telescope camera is for distance alignment between the LED tip and the detector

aperture, and the other for axis alignment of the LED. Fig. 4-3 and Fig. 4-4 show how we

align the LED axis and the distance of LED tip to detector aperture.

Fig. 4-3. Axis alignment in KRISS.

Fig. 4-4. Distance alignment in KRISS.

slightly tilted well-alignedslightly tilted well-aligned

LED tip position Detector mount

position

LED Detector mount

LED tip position Detector mount

position

LED Detector mount


12

4.1.3. Traceability

For the illuminance meter, the illuminance responsivity is calibrated using a KRISS

working standard illuminance meter, and the relative spectral responsivity is calibrated

using a KRISS working standard photodiode. Both of scales are traceable to KRISS

cryogenic radiometer. For the spectroradiometer, the relative spectral responsivity is

calibrated using a spectral irradiance standard lamp traceable to NIST spectral irradiance

scale.

4.1.4. Measurement uncertainty

Tables in the following show the detailed uncertainty budgets of the CIE B averaged LED

intensity measurement for the LEDs used in this APMP LED comparison. The uncertainty

evaluation is carried out according to Guide to the Expression of Uncertainty in

Measurement (GUM). Expanded uncertainty are evaluated at a confidence level of

approximately 95% with a coverage factor normally k = 2. Table 4-6 is the detailed

uncertainty budget of the junction voltage measurement.

Table 4-1. KRISS uncertainty budget of averaged LED intensity measurement for red LEDs

(R).

Uncertainty Component Standard u

ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion (%)

DoF Corre

lated?

repeatability 0.00 % A t 1 0.00 9 N

axis alignment: angular 0.43 % B rectangular 1 0.43 N

axis alignment: translational 0.20 % B rectangular 1 0.20 N

current feeding 0.05 % B normal 1 0.05 Y

distance setting 0.44 % B rectangular 1 0.44 N

linearity 0.05 % B rectangular 1 0.05 Y

stray light 0.10 % B rectangular 1 0.10 Y

illuminance responsivity 0.50 % B normal 1 0.50 Y

CCF 0.25 % B normal 1 0.25 Y

reproducibility 0.63 % A t 1 0.63 >30 N

Combined standard uncertai

nty (%)

normal 1.07 >20

Table 4-2. KRISS uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion (%)

DoF Corre

lated?


13









CCF 0.18 % B normal 1 0.18 Y



nty (%)

normal 1.02 >20

Table 4-3. KRISS uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion

DoF Corre

lated?









CCF 0.37 % B normal 1 0.37 Y



nty (%)

normal 1.07 >20

Table 4-4. KRISS uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion

DoF Corre

lated?






14





CCF 0.04 % B normal 1 0.04 Y



nty (%)

normal 0.79 >20

Table 4-5. KRISS uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion

DoF Corre

lated?









CCF 0.18 % B normal 1 0.18 Y



nty (%)

normal 0.75 >20

Table 4-6. KRISS uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe Probability

distributio

n

Sensitivity

coefficient

Contribut

ion (mV)

DoF Corre

lated?

sourcemeter calibration 0.05 mV B normal 1 0.05 Y

sourcemeter offset 0.10 mV B normal 1 0.10 Y

repeatability 0.04 mV A t 1 0.04 9 N

stray resistance 0.02 mV B rectangular 1 0.02 Y


nty (mV)

normal 0.12 >20


15

4.2. MIKES


A photometer, which was used for measuring the photocurrent signal, was LMT P11 SOT.

The photometer has an aperture area of 1 cm2. The relative spectral responsivity of the

photometer has been calibrated with a reference spectrometer of MIKES. The illuminance

responsivity of the photometer has been calibrated against a reference trap photometer

of MIKES using the light source at a color temperature of 2856 K.

For calculating the spectral mismatch correction factor of LEDs under comparison,

a spectroradiometer of type DM150 from Bentham Inc. was used for measuring spectral

power distribution of the LEDs.

The averaged LED intensity measurements for each LED were made at 10-cm

distance from the front tip of the LED to the entrance aperture of the photometer. To

calculate the spectral mismatch correction factor, the relative spectral power distributions

were measured by steps of 1 nm within the wavelength range of 380-780 nm and the

relative spectral responsivity of the used photometer was measured by steps of 2 nm

within the wavelength range of 380-780 nm. During the measurements, the ambient

temperature was (21.5 ± 1.0) °C and the relative humidity of air was (31 ± 5) °C.


The detectors and an LED holder (see Fig. 4-5) were mounted to a measurement rail. The

LED under calibration was mounted on an optical table using an x-y translator, a rotary

stage, and a tilt stage. The detectors were mounted to the rail carrier using a magnetic

base plate and tilt stages. The detectors and the LED under calibration were mounted on

the same optical axis using a two-beam alignment laser. The detectors were aligned

using an auxiliary mirror to get the back-reflection into the alignment laser. The

translational alignment of the LEDs was made by an x-y translator so that the laser beam

hit the tip of the LED. An angular alignment of the LEDs was made by a digital camera,

rotary stage, and tilt stage. The distance from the front tip of the LED to the entrance

aperture of the photometer was measured using a magnetic length measurement rail.


16

Fig. 4-5. Photographs of the LED holder used in the measurement of the averaged LED

intensity B in MIKES.

4.2.3. Traceability

The illuminance responsivity of the photometer used is traceable to MIKES’ reference

photometer. The reference photometer includes a precision aperture, a V(λ) filter, and a

silicon trap detector. The absolute transmittance of the V(λ) filter is traceable to the

national standard of the regular transmittance [Calibration certificate T-R 479]. The

spectral responsivity of the trap detector is traceable to a cryogenic electrical substitution

radiometer at SP in Sweden [Calibration certificate MTeP501362-025] and modeling the

spectral shape [Calibration certificate INT-028]. The determination of the area of the

precision aperture and the distance are traceable to the realization of the meter at MIKES

[Calibration certificates M-07L193 and M-08L357]. The spectral irradiance responsivity of

the spectroradiometer is traceable to the national standard of spectral irradiance

[Calibration certificate T-R 506]. The calibrations of the current-to-voltage converter

Vinculum SP042 and digital voltmeter HP 3458A are traceable to the national standards

of electricity [Calibration certificates INT-033, INT-032].


Uncertainty budgets for the averaged LED intensity B and the junction voltage of the

LEDs are presented in Tables below. The sensitivity coefficients of the uncertainty

components have been calculated as the ratio between the relative standard uncertainty

of the component and the standard deviation of the probability distribution of the

component. The uncertainty components of spectral mismatch correction are based on

Monte Carlo simulations.

Table 4-7. MIKES uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


17


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Setup-related

Repeatability 1.41 % A normal 1 1.41 11 X

LED alignment, angular

tilting

B rectangular 0.09 –

0.81 %/1°

0.79 ∞ X

LED alignment,

translational centering


1.4 %/mm

0.08 ∞ X

Photometer alignment 0.6° B rectangular 0.07 %/1° 0.04 ∞ X

Current feeding B rectangular 3 –

5 %/mA

0.03 ∞ O

Distance setting 0.095 mm B rectangular 1.9 %/mm 0.18 ∞ X

Stray light 0.10 % B rectangular 1 0.10 ∞ O

Photocurrent measurement 0.03 % A normal 1 0.03 19 X

Photometer

Illuminance responsivity 0.20 B normal 1 0.20 ∞ O

Long-term stability 0.10 B rectangular 1 0.10 ∞ O

Spectral mismatch

correction

Wavelength error in

spectral response of

photometer

B normal 0.7 –

4.8 %/nm

0.17 ∞ O

Relative spectral response

of the photometer

0.22 B rectangular 1 0.22 ∞ O

Wavelength error in LED

spectrum

B normal 0.05 –

0.25 %/nm

0.04 ∞ X

Measurement noise in LED

spectrum

0.03 B rectangular 1 0.03 ∞ X

Combined standard unce

rtainty (%)

-- -- normal -- 1.67 22 --

Table 4-8. MIKES uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Setup-related


18



tilting


0.81 %/1°

0.92 ∞ X

LED alignment,



1.4 %/mm

0.04 ∞ X



5 %/mA

0.02 ∞ O




Photometer



Spectral mismatch

correction

Wavelength error in


photometer

B normal 0.7 –

4.8 %/nm

0.15 ∞ O


of the photometer



spectrum

B normal 0.05 –

0.25 %/nm

0.04 ∞ X


spectrum



rtainty (%)

-- -- normal -- 1.73 25 --

Table 4-9. MIKES uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Setup-related



tilting


0.81 %/1°

0.70 ∞ X

LED alignment,



1.4 %/mm

0.03 ∞ X


19



5 %/mA

0.02 ∞ O




Photometer



Spectral mismatch

correction

Wavelength error in


photometer

B normal 0.7 –

4.8 %/nm

0.29 ∞ O


of the photometer



spectrum

B normal 0.05 –

0.25 %/nm

0.05 ∞ X


spectrum



rtainty (%)

-- -- normal -- 1.66 21 --

Table 4-10. MIKES uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Setup-related



tilting


0.81 %/1°

0.85 ∞ X

LED alignment,



1.4 %/mm

0.04 ∞ X



5 %/mA

0.03 ∞ O



20



Photometer



Spectral mismatch

correction

Wavelength error in


photometer

B normal 0.7 –

4.8 %/nm

0.04 ∞ O


of the photometer



spectrum

B normal 0.05 –

0.25 %/nm

< 0.01 ∞ X


spectrum



rtainty (%)

-- -- normal -- 1.68 22 --

Table 4-11. MIKES uncertainty budget of averaged LED intensity measurement for diffuser-

type green LEDs (D).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Setup-related



tilting


0.81 %/1°

0.10 ∞ X

LED alignment,



1.4 %/mm

0.01 ∞ X



5 %/mA

0.02 ∞ O




Photometer


21



Spectral mismatch

correction

Wavelength error in


photometer

B normal 0.7 –

4.8 %/nm

0.15 ∞ O


of the photometer



spectrum

B normal 0.05 –

0.25 %/nm

0.04 ∞ X


spectrum



rtainty (%)

-- -- normal -- 0.66 15 --

Table 4-12. MIKES uncertainty budget of junction voltage measurement for red LEDs (R).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?

Calibration of voltmeter B normal 1 0.02 ∞ O

Junction position

dependence

B rectangular 1 0.03 ∞ X

Stability of junction voltage A normal 1 0.05 –

0.13

19 X


rtainty (mV)

-- -- normal -- 0.06 –

0.14

26 -

39

--

Table 4-13. MIKES uncertainty budget of junction voltage measurement for green LEDs (G).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?


Junction position

dependence



0.33

19 X


rtainty (mV)

-- -- normal -- 0.19 –

0.35

24 -

49

--

Table 4-14. MIKES uncertainty budget of junction voltage measurement for blue LEDs (B).


22


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?


Junction position

dependence



0.28

19 X


rtainty (mV)

-- -- normal -- 0.24 –

0.30

25 -

32

--

Table 4-15. MIKES uncertainty budget of junction voltage measurement for white LEDs (W).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?


Junction position

dependence



0.36

19 X


rtainty (mV)

-- -- normal -- 0.25 –

0.42

35 -

193

--

Table 4-16. MIKES uncertainty budget of junction voltage measurement for diffuser-type

green LEDs (D).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?


Junction position

dependence



0.12

19 X


rtainty (mV)

-- -- normal -- 0.14 –

0.15

46 -

50

--


23

4.3. CMS-ITRI


As Fig. 4-6, the test LED is located by a mount system and the mechanism axis of LED

and detector is the same axis following the CIE 127:2007 standard. The distance between

LED and detector that using CIE condition B is 100 mm. Using the DC multiple standard

resistor, two voltage meter and DC power supply that give the LED current and monitor

the current and voltage of the junction of LED. The detector is the V(λ) optical detector

that have 100 mm2 circular aperture area and connect the optical current meter for

getting the optical signal.

Fig. 4-6. Averaged LED luminance intensity measurement system in CMS-ITRI.


The LED is mounting by a holder that has two pins connect and has two wires at the end

of holder for power current connecting. The holder is located at the top of the multiple

stages that have rotating and movement stages for alignment. By using two alignment

CCDs to check the mechanical axis of LED align to the axis of setting optical axis that is

using the two lasers for setting previously.

Detector

(100 mm2 circular aperture

) LED

Alignment CCD

Alignment CCD

100 mm


24

Fig. 4-7. LED Mounting and alignment system in CMS-ITRI.

4.3.3. Traceability

The traceability of LED averaged intensity is the V(λ) detector. The absolute response

[nA/lx] of detector is calibrated by absolute radiometer. The spectral response of optical

detector is trace to the standard optical detector by spectroradiometric system, then the

standard optical detector trace to the cryogenic radiometer system.

Fig. 4-8. Traceability of measurement system in CMS-ITRI.

Candela

definition

Absolute radiometer

Optical detector

Standard optical dete

ctor

Cryogenic radiometer

system

Spectroradiometric

System

Test LED

LED holder

Multiple stages


25


Uncertainty budget of averaged LED intensity measurement:

1. Repeatability of test LED:

The repeatability of test LED is record the optical current by using current meter several

times a day and measure several days. Calculate the standard deviation of all the data.

2. LED spatial lighting distribution:

Due to the general LED have non-uniform lighting distribution. By rotating the LED

around mechanical axis consider the misalignment error from this effect.

3. LED mechanical axis alignment:

The LED mechanical axis must coaxial of system optical axis. Consider the maximum

deviation of misalignment by rotating the LED at horizontal plane.

4. Distance setting:

Because the LED averaged intensity is calculated by Inverse Square’s law, the shorter

measurement distances the more effect from deviation of measurement distance.

Consider the maximum alignment error causing the deviation of the result.

5. Photometer calibration:

The uncertainty of standard photometer is drive from the relative expand uncertainty

calibrated by National measurement laboratory (NML) in Taiwan.

6. Spectral mismatch correction:

Because of the correction of spectrometer which the wavelength shifts affect the spectral

correction factor (SCF). Consider the wavelength shifts cause the error of SCF.

Uncertainty budget of junction voltage measurement:

1. Repeatability of test LED:

The repeatability of test LED is record the junction voltage by using voltage meter several

times a day and measure several days when measuring the LED averaged intensity.

Calculate the standard deviation of all the data.

2. Resolution of voltmeter:

To consider the drift when measure the junction voltage that is the maximum digit of

voltage meter.

3. Long-term drift of voltmeter:

Long-term drift of voltmeter is the drift of the traceability since the past. Calculate the

maximum deviation of the uncertainty drift.

4. Voltmeter calibration:

The uncertainty of voltmeter is drive from the relative expand uncertainty calibrated by


26

National measurement laboratory (NML) in Taiwan.

Table 4-17. CMS-ITRI uncertainty budget of averaged LED intensity measurement for red

LEDs (R).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Repeatability 0.037 A t 1 0.037 87 X

LED spatial light

distribution

1.462 B rectangular 1 1.462 200 O

LED mechanical axis

alignment

0.148 B rectangular 1 0.148 200 O

Distance setting 0.143 B rectangular 4 0.575 200 O

Photometer calibration 0.50 B normal 1 0.50 5000 O

Spectral mismatch

correction

0.004 B rectangular 1 0.004 200 X


rtainty (%)

-- -- normal -- 1.93 595 --

Table 4-18. CMS-ITRI uncertainty budget of averaged LED intensity measurement for green

LEDs (G).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


LED spatial light

distribution

1.462 B rectangular 1 1.462 200 O

LED mechanical axis

alignment

0.148 B rectangular 1 0.148 200 O



Spectral mismatch

correction

0.004 B rectangular 1 0.004 200 X


rtainty (%)

-- -- normal -- 1.93 594 --

Table 4-19. CMS-ITRI uncertainty budget of averaged LED intensity measurement for blue

LEDs (B).


27


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


LED spatial light

distribution

1.462 B rectangular 1 1.462 200 O

LED mechanical axis

alignment

0.148 B rectangular 1 0.148 200 O



Spectral mismatch

correction

0.474 B rectangular 1 0.474 200 X


rtainty (%)

-- -- normal -- 1.99 661 --

Table 4-20. CMS-ITRI uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


LED spatial light

distribution

1.462 B rectangular 1 1.462 200 O

LED mechanical axis

alignment

0.148 B rectangular 1 0.148 200 O



Spectral mismatch

correction

0.002 B rectangular 1 0.002 200 X


rtainty (%)

-- -- normal -- 1.93 595 --

Table 4-21. CMS-ITRI uncertainty budget of averaged LED intensity measurement for

diffuser-type green LEDs (D).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


28


LED spatial light

distribution

1.462 B rectangular 1 1.462 200 O

LED mechanical axis

alignment

0.148 B rectangular 1 0.148 200 O



Spectral mismatch

correction

0.002 B rectangular 1 0.002 200 X


rtainty (%)

-- -- normal -- 1.93 594 --

Table 4-22. CMS-ITRI uncertainty budget of junction voltage measurement for red LEDs (R).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


Resolution of voltmeter 0.003 B rectangular 1 0.003 200 O

Long-term drift of voltme

ter

0.026 B rectangular 1 0.026 200 O

Voltmeter calibration 0.001 B normal 1 0.001 5000 O


rtainty (%)

-- -- normal -- 0.06 282 --

Table 4-23. CMS-ITRI uncertainty budget of junction voltage measurement for green LEDs

(G).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?




ter

0.026 B rectangular 1 0.026 200 O



29


rtainty (%)

-- -- normal -- 0.18 208 --

Table 4-24. CMS-ITRI uncertainty budget of junction voltage measurement for blue LEDs (B).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?




ter

0.026 B rectangular 1 0.026 200 O



rtainty (%)

-- -- normal -- 0.14 215 --

Table 4-25. CMS-ITRI uncertainty budget of junction voltage measurement for white LEDs

(W).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?




ter

0.026 B rectangular 1 0.026 200 O



rtainty (%)

-- -- normal -- 0.09 234 --

Table 4-26. CMS-ITRI uncertainty budget of junction voltage measurement for diffuser-type

green LEDs (D).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?




30


ter

0.026 B rectangular 1 0.026 200 O



rtainty (%)

-- -- normal -- 0.07 267 --

4.4. PTB


Fig. 4-9 below shows the measurement setup in principle. To enable the measurement of

all the desired quantities, a special mechanism is needed. This allows the following

functionality: the alignment of the LED transfer standard to the optical axis of the system,

the rotation of the LED transfer standard around its horizontal axis φ and rotation

around its vertical axis θ. Furthermore, it allows the variation of the distance r between

the selected detector and the LED transfer standard. Opposite the LED transfer standard,

a rotating wheel is used for a quick detector selection. Additionally, there is a laser and a

CCD camera mounted to enable the easy alignment of the LED transfer standard. Due to

the rotation of φ angle, the interconnection between the power supply and the LED

under test prohibits an endless rotation.

Thus, in the case of luminous flux measurements after a little more than one

rotation, a stop is needed. The next movement will then be the turn back and so on.

Fig. 4-9. Measurement setup for averaged LED intensity in PTB.


31


Fig. 4-10 below shows the holder which was used to hold, align and operate each LED. A

high reflecting cone directly behind the installed LED allows for the indirect measurement

of the backward directed partial luminous flux of the LEDs, which also contributes to the

total luminous flux.

Fig. 4-10. Pictures of the LED holder used in the measurement of the averaged LED intensity in

PTB.

4.4.3. Traceability

The primary standards for the measured quantities are traceable to national standards.


The uncertainties are determined from up to 30 individual contributions originated in the

operation and alignment of an LED in thermal conditions influenced by the holder and

the environment. The specific properties of the measurement devices and their effects

are considered in detail. The estimated uncertainties of the contributions are maximum

for standard LED calibrations at PTB. They are listed and sorted in uncertainty budgets.

The components are treated as uncorrelated.

The next statement shows the model of determining ILED,B further on called J0:

The meaning, of input data and their uncertainties of the used variables of the model

above is given by the following table for example of a blue LED:


32

To find the uncertainty in angular alignment of an LED, several persons tried to

align the LED concerning the technical protocol (page 10, Fig. 5) by help of a two-axis

support (with ruler) and a CCD camera connected to a screen. A repeatability of 0.47°

was found, which was affected by the shape and color of the LED package up to a factor

of 1.5 larger. This maximum value is taken as standard uncertainty for the angular

alignment of the LED package.

The translational alignment of an LED is taken as the difference between the tip of

the LED and the center of the measuring system. Again from test with several persons,

the repeatability for centering the LED is estimated to be within 0.4 mm in both

directions in the yz-plane. This deviation is slightly affected by the shape and the color of

the LED package up to a factor of 1.5 larger. Due to the use of a gauge block, the

distance to the photometer is much smaller and contributions from bad repeatability are

considered during luminous intensity determination.

The angular luminous intensity distribution of the LED simulated with the

uncertainty in the alignment influences the averaged luminous intensity of the LED. Since

the luminous flux of the LED is measured by help of a goniophotometer, the angular

distribution is well known and can be approximated in the range of θ (0° < θ < 2.5°) by

the function cos(abs(θ))g. In case of the blue LEDs the values of g = 39 was found.

To simulate the effect of angular and translational uncertainty to luminous

intensity a simulated photometer is introduced. It consists of a number of small

photometers with hexagon shape (finite elements) with the same sensitivity.

To correct the temperature depending change of the LED voltage during the

measurements, the knowledge of the LED voltage at Tambient = 25 °C is needed. For this

purpose the LED was operated in an integrating sphere at different ambient

temperatures.


33

During measurements of value of the photometric quantities of the LED, the LED

current and LED voltage may drift a little. This causes a change of the photometric values

of the LED. To correct this, two exponents (a and b) for a model are needed. During the

measurements of temperature dependence, the photocurrent of the integrating sphere's

photometer was measured, too. This allows the determination of the fit parameters a and

b.

For determination of the spectral mismatch correction factor and it's standard

measurement uncertainty, a Monte Carlo Simulation was used.

Table 4-27. PTB uncertainty budget of averaged LED intensity measurement for red LEDs (R).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

LED nominal current 0 A 24.8416 0

Exponent LED current

correction

0.36 B normal 0 0 13

Photocurrent amplifier dark

reading

2.4E-7 V A normal -0.115168 -4.0E-6 10

LED voltage reading 0.0006 V A normal -2.06328 -0.17 10

LED current reading 2.0E-6 A A normal -24.8416 -0.0069 10

Photocurrent amplifier

reading

6.3E-4 V A normal 0.115 0.010 10

Exponent LED voltage

correction

1.6 B normal 6.85E-4 0.15 13

Gain of photocurrent

amplifier

646 Ω A normal -2.24E-7 -0.020 10

LED nominal voltage for

25 °C

7.31E-4 V A normal 2.06132 0.21 9

Correction factor for

straylight

0.00050 B normal 0.722602 0.050 10

Bandbass correction of

spectrometer

0.0011 B normal 0.72253 0.011 50

Straylight correction of

spectrometer

5.0E-5 B normal 0.72253 5.0E-3 50

Correction for LED

translational align

4.1E-4 B normal 0.72253 0.041 10

Photometric sensitivity of

photometer

8.9E-11

A/lx

B normal -2.61E7 -0.32 10

Distance setting 0.0002 m B rectangular 14.4506 0.40 10


34

Correction for LED angular

align

0.0021 B normal 0.72253 0.21 10

Spectral mismatch

correction factor

0.0078 B normal 0.704358 0.76 50


rtainty (%)

-- -- normal -- 0.99 89 -

Table 4-28. PTB uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

LED nominal current 0 A 70.9263 0


correction

0.13 B normal 0 0 13


reading

2.4E-7 V A normal -1.11521 -9.4E-6 10

LED voltage reading 1.1E-3 V A normal -1.30284 -0.052 10

LED current reading 2.0E-6 A A normal -70.9263 -5.1E-3 10


reading

2.5E-4 V A normal 1.11521 1E-2 10


correction

0.45 B normal 4.73E-3 0.076 13


amplifier

65 Ω A normal -8.69E-6 -0.020 10


25 °C

0.0026 V A normal 1.3 0.12 9


straylight

0.00050 B normal 2.81 0.050 10


spectrometer

1.0E-4 B normal 2.81 0.010 50


spectrometer

3.0E-5 B normal 2.81 0.0030 50

Correction for LED

translational align

3.0E-4 B normal 2.8 0.030 10


photometer

8.9E-11

A/lx

B normal -1.0E8 -0.32 10



align

0.0011 B normal 2.81 0.11 10

Spectral mismatch

correction factor

0.0035 B normal 2.82 0.35 50


35


rtainty (%)

-- -- normal -- 0.65 45 --

Table 4-29. PTB uncertainty budget of averaged LED intensity measurement for blue LEDs (B).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

LED nominal current 0 A normal 29.7646 0 ∞


correction

0.028 B normal 0 0 13


reading

7.5E-8 V A normal -0.320674 -3.0E-6 10

LED voltage reading 0.79E-3 V A normal -0.115157 -0.011 10

LED current reading 2.0E-6 A A normal -29.7646 -0.0073 10


reading

2.5E-4 V A normal 0.320674 0.010 10


correction

0.1022 B normal 0.0010674 0.013 13


amplifier

200 Ω A normal -8.1451E-7 -0.020 10


25 °C

0.0017 V A normal 0.115006 0.024 9


straylight

0.00050 B normal 0.814303 0.050 10


spectrometer

0.0010 B normal 0.814221 0.10 50


spectrometer

0.0010 B normal 0.814221 0.10 50

Correction for LED

translational align

0.0010 B normal 0.814221 0.10 10


photometer

8.9E-11

A/lx

B normal -2.9384E7 -0.32 10



align

5.7E-3 B normal 0.814221 0.57 10

Spectral mismatch

correction factor

0.0071 B normal 0.917122 0.80 50


rtainty (%)

-- -- normal -- 1.10 71 --

Table 4-30. PTB uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


36


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribut

ion (%)

Deg.

of fre

edom

Correl

ated?



correction

0.21 B normal -3.46E-6 -1.0E-4 13


reading

2.4E-7 V A normal -0.111457 -3.8E-6 10




reading

6.2E-4 V A normal 0.11 0.010 10


correction

0.61 B normal 6.94E-3 0.061 13


amplifier

646 Ω A normal -2.14E-7 -0.02 10


25 °C

2.5E-3 V A normal 0.550948 0.2 9


straylight

0.00050 B normal 0.691747 0.050 10


spectrometer

4.0E-5 B normal 0.691678 4.0E-3 50


spectrometer

1E-5 B normal 0.691678 1.0E-3 50

Correction for LED

translational align

1.6E-4 B normal 0.691678 0.016 10


photometer

8.9E-11

A/lx

B normal -2.5E7 -0.32 10



align

4.1E-4 B normal 0.691678 4.1E-2 10

Spectral mismatch

correction factor

0.0023 B normal 0.695083 0.23 50


rtainty (%)

-- -- normal -- 0.61 36 --

Table 4-31. PTB uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


37



correction

0.12 B normal 0 0 13


reading

7.6E-8 V A normal -0.036 -3.2E-6 10




reading

2.4E-4 V A normal 0.0359941 0.010 10


correction

0.45 B normal 6.6661E-5 0.035 13


amplifier

2000 Ω A normal -8.6E-9 -0.020 10


25 °C

0.0017 V A normal 0.0578258 0.012 9


straylight

0.00050 B normal 0.0860311 0.050 10


spectrometer

1.0E-5 B normal 0.0860224 0.001 50


spectrometer

1.0E-5 B normal 0.0860224 0.001 50

Correction for LED

translational align

9.7E-5 B normal 0.0860224 9.7E-3 10


photometer

8.9E-11

A/lx

B normal -3.1044E6 -0.32 10



align

1.4E-4 B normal 0.0860224 1.3E-2 10

Spectral mismatch

correction factor

0.0032 B normal 0.0863853 0.32 50


rtainty (%)

-- -- normal -- 0.62 38 --

Table 4-32. PTB uncertainty budget of junction voltage measurement of blue LED (example).


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(mV)

Deg. of

freedo

m

Correl

ated?

Calibration of voltmeter 0.000050 B rectangular 3.44 0.17 10

Junction position

dependence

0.00052 V B rectangular -1 -0.52 10


38

Reproducibility 0.00058 V A normal 1 0.58 10


rtainty (mV)

-- -- normal -- 0.80 35 --

4.5. NMIJ


The measurement of averaged LED intensity at NMIJ is based on the detector-method.

Photometer for Averaged LED Intensity (LED-photometer) composed of silicon photo-

diode, V(λ) correction filter, and circular aperture having an area of 100 mm2. "f1' value" of

the LED-photometer is 2.4.

Fig. 4-11. Calibration facility for LED luminous intensity and total luminous flux in NMIJ.


a) The laser system and the telescope with CCD camera are used for LED alignment.

b) LED holder is mounted to the gonio-stage. (see Fig. 4-12)

c) Fig. 4-13 shows picture of the LED holder. (Pin socket is used to mount LED)


39

Fig. 4-12. LED mount socket mounted to the gonio-stage in NMIJ.

Fig. 4-13. LED mount socket in NMIJ.

4.5.3. Traceability

a) Illuminance responsivity of the LED photometer ⇒ luminous intensity standard at

NMIJ.

b) Relative spectral responsivity of the LED photometer ⇒ spectral responsivity

standard at NMIJ.

c) Relative spectral distribution of the test LED ⇒ spectral irradiance standard at NMIJ.


Table 4-33. NMIJ uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


40

Illuminance responsivity

(include near-field effect)

B gaussian 1 1.0 90000 O

Temperature dependence of

illuminance responsivity 1.2 °C B rectangular 0.09 %/°C 0.10 ∞ O

Linearity of illuminance

responsivity

B rectangular 1 0.07 ∞ O

Current feeding accuracy B rectangular 1 < 0.01 ∞ O

DMM accuracy B rectangular 1 < 0.01 ∞ O

Distance setting 0.21 mm B rectangular 2 %/mm 0.42 ∞ O

Mechanical axis alignment,

angular 0.29° B rectangular 0.48 %/° 0.14 ∞ X


translational (centering)

0.58 mm B rectangular 0.48 %/mm 0.16 ∞ X

Repeatability of LED

lighting (including noise

and drift)

A t 1 0.11 6 X

Stray light B rectangular 1 0.10 ∞ O

Spectral mismatch correction factor

Spectral responsivity

calibration (including

repeatability)

A

+

B

gaussian 1 0.11 ∞ X

Spectral irradiance


repeatability)

A

+

B

gaussian 1 < 0.01 ∞ X

Wavelength uncertainty of

relative spectral

responsivity

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.19 ∞ X


LED spectral distribution

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.02 ∞ X

Effect of slit function width B rectangular 1 0.12 ∞ X

Alignment of LED B rectangular 1 0.02 ∞ X


rtainty (%)

-- -- normal -- 1.1 >>

25000

--

Table 4-34. NMIJ uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


41


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?







responsivity












and drift)

A t 1 0.05 6 X





repeatability)

A

+

B


Spectral irradiance


repeatability)

A

+

B



relative spectral

responsivity

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.18 ∞ X



Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.02 ∞ X


Alignment of LED B rectangular 1 < 0.01 ∞ X


rtainty (%) -- -- normal -- 1.2 >>

25000

--


42

Table 4-35. NMIJ uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?







responsivity












and drift)

A t 1 0.05 6 X





repeatability)

A

+

B


Spectral irradiance


repeatability)

A

+

B



relative spectral

responsivity

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.35 ∞ X



Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- < 0.01 ∞ X




43


rtainty (%)

-- -- normal -- 1.6 >>

25000

--

Table 4-36. NMIJ uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?







responsivity












and drift)

A t 1 0.13 6 X





repeatability)

A

+

B


Spectral irradiance


repeatability)

A

+

B



relative spectral

responsivity

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.04 ∞ X



Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- < 0.01 ∞ X



44



rtainty (%)

-- -- normal -- 1.1 >> 250

00

--

Table 4-37. NMIJ uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?







responsivity












and drift)

A t 1 0.02 6 X





repeatability)

A

+

B


Spectral irradiance


repeatability)

A

+

B



relative spectral

responsivity

Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.17 ∞ X



Random

0.1 nm,

systematic

0.1 nm

A

+

B

gaussian

(random f

actor),

rectangular

(systematic

factor)

-- 0.02 ∞ X


45


Alignment of LED B rectangular 1 < 0.01 ∞ X


rtainty (%)

-- -- normal -- 1.1 >>

25000

--

Table 4-38. NMIJ uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(V)

Deg. of

freedo

m

Correl

ated?

Calibration of DMM B gaussian 1 0.0001 ∞ O

Repeatability (including

effect of temperature

difference)

A gaussian 1 0.0006

~

0.0086

4 X

Junction position B rectangular 1 0.0003 ∞ X


rtainty (V)

-- -- normal -- 0.0007

~

0.0086

7 --

4.6. CENAM


As established in the comparison Protocol6, the Averaged LED Intensity measurements

were performed by using the measurement array setup in order to reproduce the CIE

Standard Condition B7, see Fig. 4-14.

Fig. 4-14. CIE Standard Condition B established for Averaged LED Intensity in CENAM.

Since the key condition to be kept in order to reproduce the CIE Standard

6 D. H. Lee, Technical Protocol on APMP Supplementary Comparison of LED Measurements, KRISS, Korea, (2008). 7 Commission International de l’Eclairage, Measurement of LEDs, Publication CIE Nº 127, Genève, (2007).

Circular aperure size A= 100 mm2

Distance d

dB=100 mm, (= 0,01 sr)

dA=316 mm, (= 0,001 sr)


46

Condition B is the established solid angle of =0.01 sr; then for a given aperture size A,

the corresponding distance d can be deduced from Eq. (4.1):

. (4.1)

Table 4-39 shows the aperture area and distance used at CENAM in order to reproduce

the sought solid angle.

Table 4-39. Parameters used at CENAM to reproduce the CIE Standard Condition B.

Aperture diameter, (mm) Aperture area, A (mm2) Distance, d (mm)

10.058 79.454 89

The selected aperture was coupled to a photometric detector, taking care of

maintaining the corresponding distance, see Fig. 4-15.

Fig. 4-15. Coupling between the aperture and photometric detector in CENAM.


As stated in the Comparison Protocol, the Averaged LED Intensity measurements

required to consider the LED geometrical axis to lie along the measurement optical axis,

see Fig. 4-16.

Fig. 4-16. Averaged LED Intensity geometry.


47

This alignment between axes required to assemble an LED mounting device

having at least six degrees of freedom for the position adjustment: translational, height,

transverse, centering angle, translational tilt angle, and transverse tilt angle. This special

mounting device consisted of an LED holder, a high load jack, an X-Y translational stage,

a rotation platform, and a pair of perpendicularly coupled goniometers, see Fig. 4-17.

Fig. 4-17. LED mounting device in CENAM.

Thus in order to define the measurement system optical axis, the height of the

LED holder was used as high reference, and propagated along the optical bench with the

use of an alignment laser beam, and fixed by using an alignment jig, see Fig. 4-18.

Fig. 4-18. Measurement system optical axis definition in CENAM.

Since the length of the several LEDs terminals was different for each device, it was

necessary to define a reference plane in order to accurately reproduce the distance d

given in Table 4-39 between the LED tip and the aperture plane; this was achieved by

LED hoder


48

locating a flat plate aside of the LED holder, see Fig. 4-19.

Fig. 4-19. Reference plane for distance stated in CIE Standard Condition B in CENAM.

With the measurement array aligned, the LEDs were placed in the holder, see Fig.

4-20, and aligned by using the reference plane defined by the flat plate and the

alignment jig; as to obtain the view of the LED as established in the Comparison Protocol,

see Fig. 4-21.

Fig. 4-20. LED insertion in the holder in CENAM.

Fig. 4-21. Lamp-type and diffuser-type LEDs alignment views in CENAM.


49

4.6.3. Traceability

The Averaged LED Intensity was measured by using a photometric detector calibrated for

photometric responsivity against the luminous intensity standard maintained at CENAM,

which is traceable to the radiant flux SI unit trough the Mexican primary standard. Fig.

4-22. shows the corresponding traceability chart for the luminous intensity

measurements carried out at CENAM, where the expanded uncertainty presented

correspond to a coverage factor of k = 2.

Fig. 4-22. Traceability chart for the luminous intensity measurements performed at CENAM.


The Averaged LED Intensity, IV, was obtained from Eq. (4.2):

, (4.2)

where ip is the photocurrent produced by the photometric detector; d is the distance

from the LED tip to the aperture plane; sV is the photometric responsivity of the detector

and F is the spectral mismatch correction factor, given by Eq. (4.3):

, (4.3)

Resistance []

Shunt Resistor

Res-61173

0,0999965

U ≤ 1,7µΩ/Ω

[V]

Multimeters

M-3457-883

M-3457-885

U = 15µV

/Ω

r

M-3457-881

U = 13 µA/A

ncia Shunt Res-

61174

U ≤ 1,7 µΩ/Ω

CNM-PNE-3

Electric

Resistance

ohm

[]

Voltage [V]

Multimeter

M-3457-883

M-3458-334

U ≤ 13 µV/V

CNM-PNE-5

Electric DC

Voltage

volt

[V]

CNM-PNM-2

Length

meter

[m]

Length [m]

Ruler

R-FOT-1

U = ± 6 µm

Area

[m2]

Aperture

U = ± 0.002 mm

CNM-PNE-13

Electric DC

current

ampere

[A]

CNM-PNF-12

Radiant Flux

watt

[W]

Responsivity

[A/W]

Photometric Detector

DF-SF-2

427 nm -723 nm

U = ± 4.15% - 0.74%

Photometric

Responsivity

[A/lx]

Photometric Detector

DF-SF-2

U ≈ ± 1.00%

Averaged LED

Intensity

0,1 cd - 1 000cd

LED’S

U = 6%

CNM-PNF-4

Luminous

Intensity

candela

[cd]

SI units

External

Laboratory

Service


50

where sph (λ) is the spectral responsivity of the used photometric detector and SA(λ) and

SLED(λ) are the spectral power distributions of the CIE Illuminant A and measured LED,

respectively.

From Eqs. (4.2) and (4.3), it is possible to identify the uncertainty components:

which are graphically shown in Fig. 4-23.

Fig. 4-23. Averaged LED Intensity uncertainty components in CENAM.

Table 4-40. CENAM uncertainty budget of averaged LED intensity measurement for red LEDs

(R).

Averaged

LED

Intensity

Multimeter resolution

Readings repeatibility

Multimeter error

i led

Ruler resolution

n d

Sv Photometric responsivity value

Axis misalign

ment

angular

translational

Stray light

Current fee

ding accura

cy

V Resistance

R


Multimeter repeatibility

Multimeter error

Resistance value

Voltage jun

ction due

to position

position vled FLT

V LED


Multimeter repeatibility

Multimeter error

F

s rel

S led

Photometric detector relative spectral responsivity

Spectroradiometer error

Spectroradiometer repeatibility


51


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedom Correl

ated?

Readings repeatability 0.07 A normal 1 0.07 14 O


Photometric responsivity

value

0.33 B normal 1 0.33 200 X

Spectral mismatch

correction

2.69 B normal 1 2.69 200 X

Current feeding accuracy 0.05 A normal 1 0.05 14 X

Junction voltage 0.004 A normal 1 0.004 14 X

Axis alignment 0.13 A normal 1 0.13 4 O

Stray light 0.01 B rectangular 1 0.01 200 X


rtainty (%)

-- -- normal -- 2.79 231 --

Table 4-41. CENAM uncertainty budget of averaged LED intensity measurement for green

LEDs (G).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedom Correl

ated?




value

0.33 B normal 1 0.33 200 X

Spectral mismatch

correction

2.97 B normal 1 2.97 200 X






rtainty (%)

-- -- normal -- 3.13 223 --

Table 4-42. CENAM uncertainty budget of averaged LED intensity measurement for blue

LEDs (B).


52


ncertainty

(%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedom Correl

ated?




value

0.33 B normal 1 0.33 200 X

Spectral mismatch

correction

2.70 B normal 1 2.70 200 X






rtainty (%)

-- -- normal -- 2.81 233 --

Table 4-43. CENAM uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

(%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedom Correl

ated?




value

0.33 B normal 1 0.33 200 X

Spectral mismatch

correction

2.74 B normal 1 2.74 200 X






rtainty (%)

-- -- normal -- 2.84 230 --

Table 4-44. CENAM Uncertainty budget of averaged LED intensity measurement for diffuser-



53


ncertainty

(%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedom Correl

ated?




value

0.33 B normal 1 0.33 200 X

Spectral mismatch

correction

3.11 B normal 1 3.11 200 X






rtainty (%)

-- -- normal -- 3.31 235 --

Table 4-45. CENAM uncertainty budget of junction voltage measurement.


ncertainty

(%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contri

bution

(%)

Deg. of

freedo

m

Correl

ated?


Multimeter resolution 0.0001 B rectangular 1 0.0001 200 X

Multimeter error 0.0005 B normal 1 0.0005 200 X


rtainty (%)

-- -- normal -- 0.002 16 --

4.7. LNE


LNE has developed a measurement set-up to measure photometric and colorimetric

characteristics of LEDs. This set-up is based on a goniophotometer designed to meet the

requirements of the CIE127 standards for averaged intensity and total flux measurements.

It is optimized for high power white LEDs measurements and was adapted for the LEDs

in the framework of the APMP-S3 supplementary comparison. The schematic of the

goniophotometer is shown on Fig. 4-24. It is 2 m long and 1.8 m high.


54

Fig. 4-24. Goniophotometer for LEDs flux measurements in LNE.

The set-up is made of the following parts:

- Optical rails to set the main frame

- A multi-axis LED mount which allow the accurate alignment of the LED along the

horizontal optical axis and with respect to the photometric center of the

goniophotometer. This device is mounted onto a horizontal axis motorised

rotation stage that rotates the LED around the optical axis. A detailed schematic

of the LED mount is shown on figure 2.

- A vertical axis motorised rotation stage on which the multi-axis LED mount is

placed.

A camera placed above the LED allows us to adjust the position of the LED with

respect to the photometric center. The photometer is mounted on an optical rail. The

Photometer

Spectrocolorimeter

LED mount

Stepping

motor driver

Camera


55

distance between the photometer and the LED can be adjusted to meet the

requirements of the measurement conditions. During the measurements the photometer

is kept steady. Laser beam is used to define the optical axis of the goniophotometer.

Fig. 4-25. LED mount in LNE.

Fig. 4-26. LED holder in LNE.

Intensity measurement is performed with a photometer, manufacturer LMT, type

P11S00, including a 11,3 mm diameter (1 cm²) sensitive area, with a very fine V()

correction (f’1 1%). The distance between the LED tip and the photometer is 100 mm

(CIE 127, condition B). The instruments used to perform the measurements are listed in Table

4-46.

Table 4-46. Instruments used on the LED photometric bench in LNE.

Instrument Manufacturer Type Function


56

V() photometer LMT P11S00 Illuminance

measurement

Picoammeter Keithley 486 Photometer current

measurement

LED power supply Agilent 3436A Stabilised LED power

supply

Shunt resistor AOIP 1000 / 228RE6 LED current

measurement

Multimeter Hewlett-Packard 3457A LED junction voltage

measurement


Alignment of the LED on the LED holder is performed using a luminance meter,

manufacturer LMT, type L1009 with reflex viewing. Then the LED is placed in front of the

photometer as shown on Fig. 4-28.

Fig. 4-27. Luminancemeter used to align the LED in LNE.

Fig. 4-28. Alignment of the LED in front of the photometer in LNE.


57

4.7.3. Traceability

Photometer

The photometer is calibrated in illuminance at LNE using a set of three standard lamps

calibrated in luminous intensity at LNE-INM. The standards lamps are calibrated using

primary realisation of the candela through filter radiometer.

Electrical Instruments

All electrical instruments with critical impact on the measurements are calibrated by the

LNE electrical department which is COFRAC (Comité Français d’Accréditation) accredited.

COFRAC is the French accreditation body.

Length

The distance between the LED and the photometer is measured using a meter calibrated

by the LNE length department which is COFRAC accredited.


Intensity measurement

Reading repeatability

This uncertainty is estimated from the standard deviation of 5 measurements performed

in the same operating conditions. The uncertainties associated to each colour are the

following:

- Red: 0.20 %

- Green: 0.30 %

- Blue: 0.50 %

- White: 0.30 %

- Diffuser: 0.09 %

Component due to axis alignment

Uncertainty evaluation is performed for horizontal, vertical and angular alignment. For

horizontal and vertical alignment contributions, the LED is moved 1 mm apart from the

photometric axis and the changes in the photometer signal is noted. For the angular

alignment contribution, the result of the goniophotometric measurements are used to

determine change in photometer reading corresponding to an angular deviation of 1°

from the optical axis. The uncertainty contributions are summarized in the following table


58

for each colour taking into account a 0.5 mm alignment accuracy for the horizontal and

vertical axis and a 0.5° alignment accuracy for the angular positioning.

LED type Horizontal alignment

(%)

Vertical alignment

(%)

Angular alignment

(%)

Red 0.020 0.035 0.25

Green 0.12 0.12 0.5

Blue 0.13 0.15 0.7

White 0.014 0.036 0.1

Diffuser 0.0050 0.032 0

Component due to distance between the LED and the photometer

The distance between the LED and the reference plane of the photometer is known with

an uncertainty of 100 µm. The associated contribution to the intensity measurement is

evaluated by measuring the changes in the photometer signal when the distance is

changed by 5 mm. The result is shown in the following table for the different LED colors.

LED type Relative uncertainty due to distance

LED-photometer

(%)

Red 0.18

Green 0.18

Blue 0.18

White 0.18

Diffuser 0.20

Component due to current feeding accuracy.

The current is measured through a 1000 resistor using a voltmeter. The resistor is

calibrated with an uncertainty of 1. 10-5. The voltmeter is calibrated with an uncertainty

of 1. 10-5. Therefore the current is measured with an uncertainty of 1.4 10-5. The current

is adjusted with an offset of 0.001 mA which corresponds to a relative error of 5. 10-5 .

The intensity is not corrected for this offset which is included in the uncertainty of the

current. The overall uncertainty on the current feeding is obtained from the uncertainty

due to the current measurement and the current offset, that is 5.2 10-5. The

corresponding uncertainty of the LED intensity measurement is determined from the

manufacturer’s data sheets. The results are summarized in the following table:

LED type Relative uncertainty due to

current feeding

(%)

Red 0.0052


59

Green 0.0042

Blue 0.0031

White 0.0042

Diffuser 0.0042

Component due to stray light in the optical bench

A black tube with apertures is placed between the photometer and the LED. The aperture

in front of the LED is 10 mm in diameter. The LED is placed 20 mm away from the holder

which is black painted, partly shiny, to reduce contribution of backward emission. With

this arrangement stray light is limited and is estimated to be < 0.01 %.

Component due to ambient temperature

The measurements are performed at 23 °C 1 °C. The measurement uncertainty due to

the uncertainty on the ambient temperature is determined from the manufacturer’s data

sheets. The results are summarized in the following table:

LED type Uncertainty due to ambient temperature

(%)

Red 0.5

Green 0.25

Blue 0.25

White 0.2

Diffuser 0.25

Component due to the calibration of the photometer

The photometer is calibrated with a relative uncertainty of 0.6%.

Component due to linearity of the photometer

For intensity measurement the illuminance measured is of the same order of magnitude

than the illuminance measured during the photometer calibration. Therefore the

uncertainty due do linearity of the photometer is < 0.02%.

Component due to spectral mismatch correction

The photometer is calibrated in relative spectral response. The LED flux measurement

results are corrected for the spectral mismatch of the photometer. The uncertainty on the

relative spectral response of the photometer is used to determine the uncertainty on the

spectral mismatch correction. This uncertainty is calculated by taking the average of the

uncertainty of the relative spectral response weighted by the spectral distribution of the


60

LED. Works using Monte Carlo techniques are underway to take into account correlation

in determining uncertainty on spectral mismatch correction. The actual uncertainties are

the following:

- Red: 0.5 %

- Green: 0.4 %

- Blue: 1 %

- White: 0.2 %

Table 4-47. LNE uncertainty budget of averaged LED intensity measurement for red LEDs (R).

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Reading

repeatability

0.2 A t 1 0.2 4 X

Axis

alignment,

angular


Axis

alignment,

translational


Distance

setting


Current

feeding

accuracy

0.0052 B rectangular 1 0.0052 ∞ X

Stray light 0.01 B rectangular 1 0.01 ∞ O

Ambiant

temperature


Calibration

of

photometer

0.6 B normal 1 0.6 ∞ O

Non-

linearity


Spectral

mismatch

correction

0.5 B normal 1 0.5 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 1.0 ∞ --

Table 4-48. LNE uncertainty budget of averaged LED intensity measurement for green LEDs

(G).

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?


61

Reading

repeatability

0.3 A t 1 0.3 4 X

Axis

alignment,

angular


Axis

alignment,

translational


Distance

setting


Current

feeding

accuracy

0.0052 B rectangular 0.8 0.00416 ∞ X


Ambiant

temperature


Calibration

of

photometer

0.6 B normal 1 0.6 ∞ O

Non-

linearity


Spectral

mismatch

correction

0.4 B normal 1 0.4 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 1.0 ∞ --

Table 4-49. LNE uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Reading

repeatability

0.5 A t 1 0.5 4 X

Axis

alignment,

angular


Axis

alignment,

translational


Distance

setting


Current

feeding

accuracy

0.0052 B rectangular 0.6 0.00312 ∞ O


Ambiant

temperature



62

Calibration

of

photometer

0.6 B normal 1 0.6 ∞ O

Non-

linearity


Spectral

mismatch

correction

1 B normal 1 1 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 1.5 ∞ --

Table 4-50. LNE uncertainty budget of averaged LED intensity measurement for white LEDs

(W).

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Reading

repeatability

0.3 A t 1 0.3 4 X

Axis

alignment,

angular


Axis

alignment,

translational


Distance

setting


Current

feeding

accuracy

0.0052 B rectangular 0.8 0.00416 ∞ O


Ambiant

temperature


Calibration

of

photometer

0.6 B normal 1 0.6 ∞ O

Non-

linearity


Spectral

mismatch

correction

0.2 B normal 1 0.2 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 0.76 ∞ --

Table 4-51. LNE uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


63

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Reading

repeatability

0.09 A t 1 0.09 4 X

Axis

alignment,

angular

0 B rectangular 1 0 ∞ X

Axis

alignment,

translational


Distance

setting


Current

feeding

accuracy

0.0052 B rectangular 0.8 0.00416 ∞ O


Ambiant

temperature


Calibration

of

photometer

0.6 B normal 1 0.6 ∞ O

Non-

linearity


Spectral

mismatch

correction

0.4 B normal 1 0.4 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 0.79 ∞ --

Junction Voltage

Repeatability

This uncertainty is estimated from the standard deviation of 20 measurements performed

in the same operating conditions. For all type of LED the uncertainty is 0.02%.

Component due to the calibration of the voltmeter

The voltmeter used for the junction voltage measurement is calibrated with an

uncertainty of 0.001 %.

Component due to position of junction voltage measurement point.

The leads of the LED are made of iron for the red LED and of copper for the green,

blue and white LED. The 4-wires device used to measure the junction voltage is located

20 mm away from the LED chip. Taking into account the geometry of the leads (40 mm

long and 0.25 mm² area) and the conductivity of the material used for the leads we

determine the voltage drop due to the leads. The results are summarized in the following


64

table.

LED type Relative voltage drop @ 20 mA

(%)

Red 0.008

Green 0.0008

Blue 0.0008

White 0.0008

Diffuser 0.0008

Table 4-52. LNE uncertainty budget of junction voltage measurement of red LEDs.

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Repeatability 0.01 A normal 1 0.01 19 X

Calibration

of voltmeter

0.001 B normal 1 0.001 ∞ O

Junction

position

dependence*


Combined

standard

uncertainty

(%)

-- -- normal -- 0.013 ∞ --

Table 4-53. LNE uncertainty budget of junction voltage measurement of green, blue, white and

diffuser-type LEDs.

Uncertainty

Component

Standard

uncertainty Ty

pe Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedom

Correlated?

Repeatability 0.01 A normal 1 0.01 19 X

Calibration

of voltmeter

0.001 B normal 1 0.001 ∞ O

Junction

position

dependence*

0.0008 B rectangular 1 0.0008 ∞ X

Combined

standard

uncertainty

(%)

-- -- normal -- 0.010 ∞ --

4.8. METAS


The measurements setup and the instruments used are illustrated in the Fig. 4-29 below.

The measurements were performed by a set of photometers of different manufactures


65

and different V(λ) matches. The luminous responsivity is individually corrected for all

photometer – LED combinations by measuring the spectral responsivity of the

photometers and spectral distribution of the LEDs.

Fig. 4-29. Schematic setup for averaged LED intensity measurement in METAS.


The LED is fixed inside a kinematic optical mount. The LED is connected through a “true”

4 wires connection. The voltage is measured at the end of the pin by gold plated

electrical connectors (yellow and green wire in the image below). The current is feed

through electrical clamps (brown and white wire).

The alignment is performed in several iterative steps in accordance with the

technical protocol of the comparison: The centering and directional adjustment is done

by a camera based system placed in front the LED on the optical axis of the photometer

bench. The distance is adjusted through visible observation through an alignment

telescope from the side. The required distance of 100 mm is assured through a

mechanical gauge block.

Photometer bench

Carrousel holding different photometers (Czibula, LMT, METAS) and the spectroradiometer

Picoammeter Vinculum

Keithley Multimeter 2010

Keithley Sourcemeter 2400, 4wires

LED holder on 4 axis-alignment holder

Visual alignment telescope

Camera based alignment telescope


66

Fig. 4-30. LED mount and wire connection in METAS.

4.8.3. Traceability

All primary quantities (i.e. illuminance, length, current, voltage etc) and secondary

quantities (temperature, humidity, etc) are traceable to national standards realized at

METAS. The detailed view of the traceability of the primary quantities is shown in the

following diagram.


The uncertainty budgets are based on the recommendation of CIE TC2-43

“Determination of measurement uncertainty in photometry”, Draft 9, 2008, and thus

following the GUM.

Cryogenic radiometer METAS

Reference Radiometer METAS

Reference Photometer Illuminant A METAS

METAS Electricity Section

Averaged LED intensity

METAS Length Section

Filterradiometer METAS

Aperture

METAS Electricity Section

Distance

ULED, ILED, IPhoto

Spectral Irradiance Standard METAS

Spectrometer METAS

Colour correction factor

IRadio

IPhoto


67

For simplicity only the uncertainty budget for a green LED is illustrated explicitly

in the following. The estimated input quantities of the other LED’s are listed in their

description.

Model for averaged LED intensity:

Description of terms:

CS1I output quantity: luminous intensity of the LED at certified conditions.

PSd = 0.100 m, distance between tip of the LED and photometer head, interval

±0.00020 m with rectangular power distribution (RPD), converted into standard

measurement uncertainty (MU) )( PSdu = (0.000200/ 3 = 0.000115) m; Type B

with degree of freedom (DOF) v , no correlation.

PS1y = 0.714242 V, DVM signal photometer, 10n independent readings, the

standard deviation of the mean (SDM) is taken as standard MU

PS1yu 0.000006 V and is significantly larger than the resolution; Type A with

DOF 9v , no correlation.

PS0y = 0.000048 V, DVM dark signal photometer, 10n independent readings, the

SDM is taken as standard MU PS0yu 0.000004 V and is significantly larger

than the resolution; Type A with DOF 9v , no correlation.

CR1s = 25.722 nA/lx, luminous responsivity of the photometer certified with relative

expanded 2k MU CR1rel sU = 0.008, converted into absolute standard MU

CR1su = (25.722*0.008/2 = 0.1029) nA/lx; Type B with DOF v , no

correlation.

Pc = 1.00000, calibration factor for the DVM certified with relative expanded 2k

MU Prel cU = 0.0001, converted into absolute standard MU

Pcu = 1.00000*0.0001/2 = 0.00005; Type B with DOF v , no correlation.

PS1G = 100.0020 K , gain setting resistance (of the picoammeter) certified with

relative expanded 2k MU PS1rel GU = 0.00002, converted into absolute

standard MU PS1Gu = (100.0020*0.00002/2 = 0.001) K; Type B with DOF

v , no correlation.

SMCf = 1.0067, spectral mis-match correction factor of the green LED. The factor and its

uncertainty depend on the spectral distribution of the LED source (and the spectral

responsivity of the photometer). The relative expanded 2k MU )( SMCfU =

)()(

)(

aS1S1PSS1

PPPSP

PS1

P

CR1

PS0PS1PSCS1

xSSS

m

SN

SSMC

dkhTdd

gdd

J

Jf

G

c

s

yydI

JS

111

2

21

21


68

0.010, converted into standard MU )( SMCfu = (1.0067*0.010/2)= 0.005.

Typical values including standard uncertainties (k = 1) for the other LED colours

are: SMCf (blue) = (1.026 ± 0.015), SMCf (red) = (0.991 ± 0.005), and SMCf

(white) = (1.007± 0.003).

SJ = 20.000 mA, current of the current source with a relative expanded 2k MU

)( SJU = 2E-4, converted into absolute standard MU )( SJu =

(20.000*0.0002/2 = 0.002) mA; Type B with DOF v , no correlation.

SNJ = 20 mA, nominal current, no uncertainty.

JSm = 0.75, exponent relating relative luminous output intensity with electrical input

current (based on the datasheet of the green LED) with absolute standard

uncertainty 020)( .mu JS . The values (included their expanded MU) of the other

colours are: JSm (blue) = 0.72 ± 0.04, JSm (red) = 0.94 ± 0.04, and JSm (white)

= 0.80 ± 0.04, all Type B with DOF v , no correlation.

PSP dd = (0 ± 0.2) mm/100 mm, distance alignment of photometer head within

interval with RPD, converted into standard MU )( PSP ddu = 0.2/(100*

3 ) = 0.0012; Type B with DOF v , no correlation.

)( PPg = 0.0, angular misalignment of photometer head within interval max 1° with

RPD converted into standard MU 20/)180/1())(( 2 PPgu = 0.00007;

Type B with DOF v , no correlation.

PSS1 dd = (0 ± 0.2) mm/100 mm, distance alignment of LED tip within interval with

RPD, converted into standard MU PSP ddu = 0.2/(100* 3 ) = 0.0012; Type B

with DOF v , no correlation.

S1 = -0.0019 -1K , relative temperature coefficient of the green LED (based on the

datasheet ) with standard MU S1u = (0.0002/2 = 0.0001) -1K ; Type B with

DOF v , no correlation. For other LED’s the temperature coefficient is

estimated as: S1 (red) = (-0.0074 ± 0.0005) -1K , S1 (blue) = (0.00175 ±

0.00020) -1K , S1 (white) = (0.0016 ± 0.0005)

-1K ,

aS1T = 0.0 °C, above nominal ambient temperature near lamp, with standard MU

aS1Tu = (0.5/ 3 = 0.28) °C; Type B with DOF 1000v , no correlation.

)( 11 SSh = 0.0, angular misalignment of the LED within interval 1S 2° with RPD

converted into standard MU 202)(2

11 ghu SS = 0.0025;

Type B with DOF v , no correlation. )log(cos/)5.0log( 5.0g = 9.0, is

determined from the FMHW 50. (datasheet of the green LED). For the other

LED’s the values are g (red) = 6.9, g (blue) = 9.0, g (white) = 3.2, g (diffuse)

= 1.0. The uncertainty on g is neglected.


69

)( xS dk 1 = 0.0, lateral misaligement of the LED within interval xd 0.5 mm with

RPD converted into standard MU 20)100/5.0arctan()(2

1 gdku xS =

0.00005, Type B with DOF v , no correlation, g is taken as above.

The following quantities were ignored

- The influence of the ambient temperature uncertainty on the photometer as a temperature

stabilized photometer was used.

- The influence of the ambient temperature, electrical current (of the LED supply) and the

mechanical alignment on the spectral mis-match correction factor.

- straylight effects (not estimated).

- ageing of the photometer as the detector was calibrated just before use.

- ageing of the DUT as no relevant information was available.

- The influence of the uncertainty of the surface area of the photometer, estimated to be

(100.00 ± 0.01) mm2.

Sensitivity coefficients:

PS

CS

PS

CS

d

I

d

Ic 11

1 2 55.9027 cd/m

1

1

1

12

PS

CS

PS

CS

y

I

y

Ic 3.914 cd/V

1

1

0

13

PS

CS

PS

CS

y

I

y

Ic - 3.914 cd/V

1

1

1

14

CR

CS

CR

CS

s

I

s

Ic -0.1087 cd/V

p

CS

p

CS

c

I

c

Ic 11

5 2.795 cd

PS1

1

PS1

16

G

I

G

Ic CSCS

-0.027951 cd/kΩ

SMC

CS

SMC

CS

f

I

f

Ic 11

7 2.777 cd

S

CSJS

S

CS

J

Im

J

Ic 11

8 0.1048 cd/mA

SN

SCS

JS

CS

J

JI

m

Ic log1

110

0.000 cd

1

PSP

111 2

)(CS

CS Idd

Ic 5.5903 cd

1

112

)(CS

pp

CS Ig

Ic

2.795 cd

1

PSS1

113 2

)(CS

CS Idd

Ic -5.5903 cd

11

S1

114 CSaS

CS ITI

c

0.000 cd K

1S1

1

115 CS

aS

CS IT

Ic 0.00531 cd K

-1

1

11

116

)(CS

SS

CS Ih

Ic

-2.795 cd

1

1

117

)(CS

xS

CS Idk

Ic -2.795 cd

Table 4-54. METAS uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


70


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contribut

ion (%)

Deg. of

freedo

m

Correl

ated?

Distance photometer

bench PSd

1.15E-4 m B rectangular 13.7847

cd/m

0.23 ∞ X

Mean value photometer

signal PS1y

6E-6 V A t 0.3853 cd/V <0.001 9 X


dark signal PS0y

4E-6 V A t -0.3853 cd/V <0.001 9 X

Responsivity photometer

CR1s

0.1029

nA/lx

B normal -0.02680

cd·lx/nA

-0.40 ∞ O

Calibration factor DVM

gain resistor Pc

5E-5 B normal 0.6892 cd 0.005 ∞ O

Gain resistor photometer

PS1G 0.001 kΩ B normal -6.8923E-04

cd/kΩ

<0.001 ∞ O

Spectral mismatch

correction factor SMCf

0.005 B normal 0.6955 cd 0.50 ∞ X

Measured current of LED

SJ 0.002 mA B normal 0.0324

cd/mA

0.009 ∞ X

Intensity to current

exponent JSm

0.02 B normal 0 0 ∞ X

Relative distance

variation, photomter

PSP dd

0.0012 B rectangular 1.3785 cd 0.24 ∞ X

Angular alignment

photometer )( PPg

7E-5 B rectangular 0.6892 cd 0.007 ∞ X

Relative distance

variatioin PSS1 dd

0.0012 B rectangular -1.3785 cd -0.24 ∞ X

Temperature coefficient

of LED S1

0.0001 K-1

B normal 0 0.007 ∞ X

Temperature above

nominal temp. aS1T

0.28 K B rectangular 0.0051 cd/K 0.21 ∞ X

Angular tilt )( 11 SSh 0.002 B rectangular -0.6892 cd -0.20 ∞ X

Lateral misalignment

)( xS dk 1

5R-5 B rectangular -0.6892 cd -0.005 ∞ X

Combined standard unc

ertainty (%)

-- -- normal -- 0.82 > 1000 --

Table 4-55. METAS uncertainty budget of averaged LED intensity measurement for green

LEDs (G).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contribut

ion (%)

Deg. of

freedo

m

Correl

ated?


71

Distance photometer

bench PSd


cd/m

0.23 ∞ X


signal PS1y

6E-6 V A t 3.9134 cd/V <0.001 9 X


dark signal PS0y

4E-6 V A t -3.9134 cd/V <0.001 9 X


CR1s

0.1029

nA/lx

B normal -0.1087

cd·lx/nA

-0.40 ∞ O


gain resistor Pc

5E-5 B normal 2.7951 cd 0.005 ∞ O


PS1G 0.001 kΩ B normal -0.0280

cd/kΩ

-0.0010 ∞ O

Spectral mismatch


0.005 B normal 2.7765 cd 0.50 ∞ X



cd/mA

0.008 ∞ X


exponent JSm

0.02 B normal 0 0 ∞ X

Relative distance


PSP dd


Angular alignment

photometer )( PPg


Relative distance

variatioin PSS1 dd



of LED S1

0.0001 K-1


Temperature above

nominal temp. aS1T




)( xS dk 1



ertainty (%)

-- -- normal -- 0.80 > 1000 --

Table 4-56. METAS uncertainty budget of averaged LED intensity measurement for blue

LEDs (B).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contribut

ion (%)

Deg. of

freedo

m

Correl

ated?

Distance photometer

bench PSd


cd/m

0.23 ∞ X


signal PS1y

6E-6 V A t 0.4000 cd/V <0.001 9 X


72


dark signal PS0y

4E-6 V A t -0.4000 cd/V <0.001 9 X


CR1s

0.1029

nA/lx

B normal -0.03495

cd·lx/nA

-0.40 ∞ O


gain resistor Pc

5E-5 B normal 0.8991 cd 0.005 ∞ O


PS1G 0.001 kΩ B normal -8.9911E-04

cd/kΩ

<0.001 ∞ O

Spectral mismatch


0.015 B normal 0.8739 cd 1.46 ∞ X



cd/mA

0.01 ∞ X


exponent JSm

0.02 B normal 0 0 ∞ X

Relative distance


PSP dd


Angular alignment

photometer )( PPg


Relative distance

variatioin PSS1 dd



of LED S1

0.0001 K-1

B normal 0 0 ∞ X

Temperature above

nominal temp. aS1T

0.28 K B rectangular -0.0016 cd/K -0.05 ∞ X



)( xS dk 1



ertainty (%)

-- -- normal -- 1.59 > 1000 --

Table 4-57. METAS uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contribut

ion (%)

Deg. of

freedo

m

Correl

ated?

Distance photometer

bench PSd


cd/m

0.23 ∞ X


signal PS1y

6E-6 V A t 0.3913 cd/V <0.001 9 X


dark signal PS0y

4E-6 V A t -0.3913 cd/V <0.001 9 X


CR1s

0.1029

nA/lx

B normal -0.02683

cd·lx/nA

-0.40 ∞ O


73


gain resistor Pc

5E-5 B normal 0.6901 cd 0.005 ∞ O


PS1G 0.001 kΩ B normal -6.9008E-04

cd/kΩ

<0.001 ∞ O

Spectral mismatch


0.003 B normal 0.6855 cd 0.30 ∞ X



cd/mA

0.008 ∞ X


exponent JSm

0.02 B normal 0 0 ∞ X

Relative distance


PSP dd


Angular alignment

photometer )( PPg


Relative distance

variatioin PSS1 dd



of LED S1

0.0001 K-1

B normal 0 0 ∞ X

Temperature above

nominal temp. aS1T

0.28 K B rectangular -0.0011 cd/K -0.04 ∞ X



)( xS dk 1



ertainty (%)

-- -- normal -- 0.66 > 1000 --

Table 4-58. METAS uncertainty budget of averaged LED intensity measurement for diffuser-



ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contribut

ion (%)

Deg. of

freedo

m

Correl

ated?

Distance photometer

bench PSd

1.15E-4 m B rectangular 1.7080 cd/m 0.23 ∞ X


signal PS1y

6E-6 V A t 0.0397 cd/V <0.001 9 X


dark signal PS0y

4E-6 V A t -0.0397 cd/V <0.001 9 X


CR1s

0.1029

nA/lx

B normal -0.00332

cd·lx/nA

-0.40 ∞ O


gain resistor Pc

5E-5 B normal 0.0854 cd 0.005 ∞ O


PS1G 0.001 kΩ B normal -8.5399E-06

cd/kΩ

<0.001 ∞ O


74

Spectral mismatch


0.007 B normal 0.0836 cd 0.69 ∞ X



cd/mA

0.008 ∞ X


exponent JSm

0.02 B normal 0 0 ∞ X

Relative distance


PSP dd


Angular alignment

photometer )( PPg


Relative distance

variatioin PSS1 dd



of LED S1

0.0001 K-1

B normal 0 0 ∞ X

Temperature above

nominal temp. aS1T




)( xS dk 1



ertainty (%)

-- -- normal -- 0.90 > 1000 --

Model for junction voltage:

L0L1aL0aLrelL,CLL 1 UUTTccU

Description of terms:

LU output quantity: junction voltage of the LED at certified conditions.

Lc = 1.0000, DVM calibration factor with absolute standard MU )( Lcu = 1E-5;


Cc = 1.000, non-equivalence of the contact. We have tried different connectors. A

spread in junction voltages have been observed even with 4 wires connections. The

estimated absolute standard MU )( Ccu = 0.0020; Type B with DOF v , no

correlation.

relL, = 0.000015, relative temp. coefficient according standard MU )( relL,u = 5E-6;


aLT = 22.6 °C, ambient temperature with ±0.5°C RPD, converted into standard MU

)( aLTu = (0.5/ 3 = 0.29)°C; Type B with DOF v , no correlation.

aL0T = 23.0 °C, nominal ambient temperature, no uncertainty

L1U = 1.94058 V, measured voltage (DVM), with standard MU of L1Uu = 0.00011


75

V, 361 readings, Type A with DOF 360v , no correlation.

L0U = 0.00002 V, measured zero voltage (DVM), with standard MU of L1Uu =

0.00011 V, 361 readings , Type A with DOF 360v , no correlation.

Table 4-59. METAS uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

DVM mean value voltage

L1U

0.00011 V A t 0.99999

V/V

0.0055 360 X

DVM calibration factor

Lc

1.0E-5 B normal 1.94055 V 0.0010 ∞ O

Relative temperature

coefficienct relL,

5.0E-6 K-1

B normal -0.77622

VK

-0.0002 ∞ X

Ambient temperature aLT 0.29 °C B rectangular 0.00003

V/°C

0.0004 ∞ X

Offset voltage L0U 0.00011 V A t -0.99999

V/V

-0.0055 360 X

Non-equivalence of contact

Cc

0.0021 B rectangular 1.94055 V 0.21 ∞ X


rtainty (V)

-- -- Normal -- 0.21 >1000 --

4.9. NMC-A*STAR


The measurement setup of the averaged LED intensity is shown in Fig. 4-31 and Fig. 4-32.

The LED light receptor is an integrating sphere with a 1 cm2 opening input port

according to the CIE requirement. The LED light received by the receptor is fed to a

spectroradiometer (Model OL770 made by Optronic Laboratories) through an optical

fibre. The spectroradiometer uses a cooled CCD detector with 128 x 1024 elements

covering the wavelength range of 380 nm to 1100 nm. Its bandwidth (FWHM) is about

3.5 nm and the data interval is 1 nm.

The LED is driven by a programmable DC Source (Model 7651 made by

Yokogawa). The driving current is measured using a calibrated precision resister and a

calibrated digital volt meter (Model 34420A made by Hewlett Packard). The electric

connection in the LED holder is a 4-wire connection to achieve the accurate

measurement of the LED forward voltage.


76

Fig. 4-31. LED averaged intensity measurement setup in A*STAR.

Fig. 4-32. Photograph of the LED averaged intensity measurement setup in A*STAR.


Fig. 4-33 is a picture of the LED light receptor and Fig. 4-34 shows the LED holder.

The alignment laser and the precision auto level 2 (telescope) are used to define

the measurement axis. The angular and centre alignment of the LED is monitored by a

video camera attached to the auto level 2. Fig. 4-35 shows a picture of the correctly

aligned LED viewed by the camera. The auto level 1 and the precision rail as shown in

Fig. 2 are used to set the distance of 100 mm between the LED and the receptor

accurately.

LED

Spectral irradiance

standard lamp Shutter

Alignment

laser

Auto level 1

(telescope)

Auto level 2

(telescope)

Video

Camera

Standard

photometer

head

LED light

receptor


77

Fig. 4-33. LED receptor;

Fig. 4-34. LED holder;

Fig. 4-35. LED alignment in A*STAR.

4.9.3. Traceability

The relative spectral responsivity of the spectroradiometer is calibrated by a spectral

irradiance standard lamp traceable to NMC’s spectral irradiance scale. The stray light

error of the spectroradiometer is corrected using cut-on filters. The absolute luminous

responsivity of the spectroradiometer is calibrated using a standard photometer traceable

to NMC’s luminous intensity scale. The average luminous intensity is calculated by

integrating the spectral irradiance measured by the spectroradiometer. The same data is

also used to calculate the emitted colour of the LED (S3c).


Tables in the following are the detailed uncertainty budgets of the CIE B averaged LED

intensity measurement for the LEDs used in this APMP LED comparison.

The uncertainty evaluation is carried out according to Guide to the Expression of

Uncertainty in Measurement (GUM). The artefact-dependent uncertainties shown in the

table with * adopt the largest uncertainty values registered among the same type of LEDs

measured. Expanded uncertainty are evaluated at a confidence level of approximately 95%

with a coverage factor normally k = 2.

Table 4-60. A*STAR uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Calibration of standard

photometer

B normal 1 0.550 ∞ Yes


78

Drift of the standard

photometer

B rectangular 1 0.116 ∞ Yes

Spectroradiometer transfer

measurement (non-

linearity)*

B rectangular 1 0.058 ∞ No

LED axis alignment,

angular

Included in the component “Reproducibility” of three independent

measurements.

LED axis alignment,

translational


measurements.

Distance measurement 0.289 % B rectangular 2 0.578 ∞ Yes

Calibration of current

feeding

0.0058 % B rectangular 0.8 0.005 ∞ Yes

Scattered light including

reflection from holder


Wavelength scale of

spectroradiometer*

0.2 nm B rectangular 2.17 %/nm 0.434 ∞ No

stray light correction of

spectroradiometer (20 % of

correction)*


Reproducibility A t 1 0.520 2 No


rtainty (%)

-- -- normal -- 1.1 37 --

Table 4-61. A*STAR uncertainty budget of averaged LED intensity measurement for green

LEDs (G).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


photometer



photometer



measurement (non-

linearity)*


LED axis alignment,

angular


measurements.

LED axis alignment,

translational


measurements.



feeding






79

Wavelength scale of

spectroradiometer*




correction)*




rtainty (%)

-- -- normal -- 0.94 107 --

Table 4-62. A*STAR uncertainty budget of averaged LED intensity measurement for blue

LEDs (B).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


photometer



photometer



measurement (non-

linearity)*


LED axis alignment,

angular


measurements.

LED axis alignment,

translational


measurements.



feeding





Wavelength scale of

spectroradiometer*




correction)*




rtainty (%)

-- -- normal -- 1.1 37 --

Table 4-63. A*STAR uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


80


photometer



photometer



measurement (non-

linearity)*


LED axis alignment,

angular


measurements.

LED axis alignment,

translational


measurements.



feeding





Wavelength scale of

spectroradiometer*




correction)*




rtainty (%)

-- -- normal -- 0.92 1557 --

Table 4-64. A*STAR uncertainty budget of averaged LED intensity measurement for diffuser-



ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


photometer



photometer



measurement (non-

linearity)*


LED axis alignment,

angular


measurements.

LED axis alignment,

translational


measurements.



feeding



81




Wavelength scale of

spectroradiometer*




correction)*




rtainty (%)

-- -- normal -- 1.0 46 --

Table 4-65 is the detailed uncertainty budget of the junction voltage

measurement, representatively presented for the red LEDs. The artefact-dependent

uncertainties shown in the table with * adopt the largest uncertainty values registered

among the same type of LEDs measured.

Table 4-65. A*STAR uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribut

ion (V)

Deg.

of fre

edom

Correl

ated?

Calibration of DVM B normal 1 9.5E-5 ∞ Yes

Position of junction (0.05

Ω)

B rectangular 1 5.78E-4 ∞ No

Drift of junction voltage B rectangular 1 1.73E-4 ∞ No

Reproducibility* A t 1 7.64E-4 5 No


rtainty (V)

-- -- normal -- 9.8E-4 13 --

4.10. VSL


The quantity for average LED intensity and total luminous flux of LEDs (as defined by the

key-comparison protocol) are measured with a goniometer facility specifically designed

and build for small single LED light sources. The facility is based on the method where

the light source is turned and the detector stands still. Therefore the facility consists out

of a detector platform and a turn-able light source unit. The light source unit includes

two rotation stages, a LED mounting unit and one linear translation stage. The linear


82

translation stage is applied to be able to change the distance between the turn-able

light source unit and the detector platform. The two rotation stages are perpendicular

mounted to each other so that the LED can be rotated exactly in the midpoint of each

stage.

The detector platform consists out of an illuminance meter with a circular

aperture with a surface of 100 mm2 and an array-spectroradiometer (SRM). The SRM is

used to correct for colour mismatch introduced by the detector and the individual LED. In

order to reduce stray light a baffle was places between the detector platform and the

turn-able light source unit. The aperture of the baffle was large compare to the diameter

of the detector and the LED to be measured.

Fig. 4-36. Schematic drawing of LED goniometer facility at VSL.


The LED is fixed in a holder, which is mounted into a mounting unit. The mounting unit

is mounted on the turn-able light source unit consisting out of the two rotation stages.

The LED holder is shown in the following figure.

Fig. 4-37. VSL LED holder.


83

The LED holder clamps the two LED pins with two parallel copper plates. The

copper plates are connected to the current source which provides the LED with operating

current. The mounting unit allows one to translate the LED in both vertical as well as

horizontal direction, and also to tilt the LED. This alignment unit is in turn mounted to

the two rotation stages. The layout of the alignment system of the LED facility together

with the mounted holder is shown in the following figure.

Fig. 4-38. Turn-able light source unit of the LED goniometer facility at VSL.

In Fig. 4-38, one sees the LED mounted on the mounting unit fixed on a two axis

rotational system. The alignment of the LED with regards to the detector as well as axis

of rotation is done as follows:

1. A high resolution camera is placed perpendicular to the mounted LED.

2. The mounted LED is rotated and visually inspected by using the high resolution camera.

3. If the mounted LED is in the centre of the rotational axis, no movement is detected

with the camera, otherwise translation is observed. The mounted LED is then

iteratively adjusted until no translation of the mounted LED is visible with the camera.

This is iteratively repeated also for the polar rotation. When varying the polar angle the

alignment criteria was that the location of the LED tip remained constant.

4. The mounted LED and illuminance detector are then optically aligned with the double

alignment laser.

The nominal distance between LED and detector is brought to 100 mm by making

use of an electronic translation stage where the LED alignment axes are mounted on, as

well as a calibrated gauge block of nominal length 100 mm. The gauge block is placed

against the detector reference surface and the LED is translated precisely until contact is

made with the gauge block. This translation distance is recorded. The gauge block is

then removed and the LED is translated back to the correct position. The distance is then

100 mm between detector and LED. The following figure illustrates this graphically.


84

Fig. 4-39. Schematic drawing of the detector versus LED distance determination at VSL.

4.10.3. Traceability

The average LED intensity measurement of an LED at VSL has as the traceability route as

shown in Fig. 4-40.

Fig. 4-40. Traceability of an average luminous intensity measurement of an LED at VSL.

The spectral responsivity scale is derived from an Absolute Cryogenic Radiometer

(ACR) by using a double monochromator facility 8 . The same facility is used for the

determination of the illuminance responsivity by using a scanning beam method and the

relative spectral irradiance responsivity of the illuminance meter 9 . Knowing the

illuminance responsivity of an illuminance meter and using a calibrated gauge block one

can determine the luminous intensity of a LED. The gauge block is calibrated and

traceable to the national standard for length. Each measurement within the traceability

chain is conducted by using digital multimeters for measurement of detector current, LED

current and LED voltage. These measurements are traceable to the national standard for

current and voltage by the use of calibrated meters.

8 Comparison of monochromator-based and laser-based cryogenic radiometry, Metrologia 1998, 35, 431-435. 9 Novel calibration method for filter radiometers, Metrologia 1999, 36, 179-182.

Cryogenic radiometer VSL Spectral responsivity scale

(A/W)

ACR facility VSL Illuminance responsivity

(A/lx)

LED Goniomter facility VSL Average luminous intensity and total

luminous flux (cd) and or (lm)

Electrical department for the traceability to the national standard of current and voltage (A) and (V)

Length department for the traceability to the national standard of length (m)


85


After the LED and detector are aligned, the following steps are performed to measure

the average LED intensity of each of the fourteen LEDs respectively:

1. The LED is brought to an operating current of nominal 20 mA.

2. The whole setup is enclosed by a thermal insulation box and allowed to stabilize for at

least 20 minutes.

3. The measurement of the illuminance at different angles are performed to investigate

the circle symmetry of the illuminance, i.e the LED is rotated in the perpendicular

direction with regards to the illuminance detector.

4. The stray light was measured by blocking light only on the optical axis, through the use

of a blocking strip.

5. The dark signal was measured, by closing the baffle situated in front of the detector

completely.

6. The average luminous intensity of the LED is calculated knowing the illuminance and

distance between detector and LED. This done as is shown in the following model

equation.

Model equation for the averaged LED intensity:

.11 2

__

22 RSA

UU

RSA

UREI

v

sl

v

cvv

Ev is the measured illuminance of the LED,

Sv is the responsivity of the reference standard illuminance meter,

Uc is the corrected measured voltage,

Ul is the measured voltage with shutter open,

Us is the measured voltage due to stray light, including dark signal. This is done by

blocking light on optical axis, for the straight light. For the dark signal the light

was blocked by a shutter.

Av is the amplification factor ,

R is the distance between the LED and the detector, which is 100mm in our case.

The responsivity is corrected for the colour mismatch. This is so since the spectral

responsivity of the detector, as well as the emitted spectrum of the LED are known. One

can then perform the required correction. The colour correction factor is calculated as

stated in the following equation:

.)()(

)()('

det

LV

LVF

CIE


86

F’ is the correction factor for colour mismatch due to the detector.

VCIE

(λ) is the luminous sensitivity function as defined by the CIE,

VDET

(λ) is the spectral responsivity of the detector which is measured

L (λ) is the measured spectrum of the LED.

An example of an illuminance measurement is shown in Fig. 4-41. As can be

seen, there is strong angle dependence. Since the LED was aligned mechanically with its

casing/lens as reference, this dependence is thought to be due to the optical and

geometrical axis of the LED not coinciding. It is thus important which point is taken as

reference.

Fig. 4-41. An example illuminance measurement of a LED determined at different angles

measured in VSL.

The value at position 0 degrees was chosen to be used when calculating the

average intensity value. This position corresponds to the following geometrical position

of the LED. If one looks perpendicular at the front of the LED one can see that one side

is not round, but flat. That flat part is taken as reference and is always kept at the left

when inspected with the camera for alignment positioned at the same position as the

illuminance meter. This is schematically shown in Fig. 4-42. Here one sees a schematic

drawing of the LED casing/lens as seen from the front, with the LED chip in die centre.

258

260

262

264

266

0 100 200 300 400

Illu

min

ance

/a.u

.

Angle /degrees


87

Fig. 4-42. Front view of an LED.

The comparison protocol states that the participant describes the total uncertainty

in detail for the LEDs of each color. As the total uncertainty of each LED is depending on

individual components the uncertainty from one LED to one other is different. Knowing

this we chose to present a detailed uncertainty budget of that LED that has the lowest

uncertainty, instead of determining the average total uncertainty of the LEDs with the

same color. This was done since no information is given how to determine the average

uncertainty of a group of LEDs. The detailed uncertainty budgets are summarized in the

tables below.

Table 4-66. VSL uncertainty budget of averaged LED intensity measurement for red LEDs (R).

Uncertainty Component Standard

uncertain

ty (%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedo

m

Corre

lated

Axis alignment,

translational

A normal 1 0.25 28 X

Axis alignment, angular B rectangular 1 0.08 ∞ X

Current feeding of LED B normal 1 0.01 ∞ O

Reproducibility B normal 1 0.01 ∞ X

Detector readout A normal 1 0.04 9 O

Stray light A normal 1 0.03 9 O

Trans-impedance amplifier B normal 1 0.001 ∞ O

Responsivity of the

detector (calibration)

B normal 1 0.15 ∞ O

Spectral mismatch

correction of detector


Non-uniformity of source B rectangular 1 0.08 ∞ X

Distance between LED and

detector


Combined standard

uncertainty (%)

-- -- normal -- 0.70 ∞ --


88

Table 4-67. VSL uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


uncertain

ty (%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedo

m

Corre

lated

Axis alignment,

translational








Responsivity of the



Spectral mismatch





detector


Combined standard

uncertainty (%)

-- -- normal -- 0.76 ∞ --

Table 4-68. VSL uncertainty budget of averaged LED intensity measurement for blue LEDs (B).


uncertain

ty (%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedo

m

Corre

lated

Axis alignment,

translational








Responsivity of the



Spectral mismatch





detector


Combined standard

uncertainty (%)

-- -- normal -- 0.72 ∞ --

Table 4-69. VSL uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


89


uncertain

ty (%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedo

m

Corre

lated

Axis alignment,

translational








Responsivity of the



Spectral mismatch





detector


Combined standard

uncertainty (%)

-- -- normal -- 0.58 ∞ --

Table 4-70. VSL uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


uncertain

ty (%) Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribution

(%)

Deg. of

freedo

m

Corre

lated

Axis alignment,

translational








Responsivity of the



Spectral mismatch





detector


Combined standard

uncertainty (%)

-- -- normal -- 0.80 ∞ --


measurement.


90

Table 4-71. VSL uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribut

ion (%)

Deg.

of fre

edom

Correl

ated?

Calibration of DVM B normal 1 1.2E-5 ∞ O

Junction position

dependence


Reproducibility* A t 1 0.0001 9 X


rtainty (%)

-- -- normal -- 0.081 ∞ --

4.11. NMIA10


The averaged luminous intensity of each LED was measured using a windowless silicon

detector mounted behind a 100 mm2 area round precision aperture located 100 mm in

front of the tip of each LED. Simultaneously the relative spectral intensity was measured

using an array spectrometer. One end of an optical fibre was placed next to, and behind,

the precision aperture and directed towards the LED, the other end of the fibre was

connected directly to the spectrometer.

The luminous intensity was calculated using the signal obtained from the silicon

detector, the relative spectral response of the silicon detector, knowledge of the

geometry of the measurement setup, the values of relative spectral irradiance of each

LED and the defined values of CIE V(λ) 1931.


For the measurements of LED intensity, each LED was mounted in a custom made

aluminium LED mount with the front surface of the mount painted with spectrally non-

selective gloss black paint. A separate aluminium base was provided for the diffused

LEDs.

Each aluminium mount was set up to be within 0.1 of perpendicular to the

measurement axis of the receiving radiometer by using a laser/mirror alignment

technique. Since the flanged LEDs are not parallel sided, orthogonality of the LEDs

10 The technical report and uncertainty budgets of NMIA are not reviewed by the participants due to the delayed submission.


91

relied upon the orthogonality of the LED base flange to the measurement axis. A value

of 0.5° was used for uncertainty calculations, allowing for imperfections in each diode

for these LEDs.

For the diffused diodes, which were not flanged, the aluminium mount provided a

close fit to the parallel sides of the diode, again 0.5° was allowed for uncertainty

calculations.

Each LED aluminium base was fitted to a standard kinematic mount and placed

on the receiving kinematic base on top of a special carriage having five degrees of

freedom in its physical adjustments as shown in Fig. 4-43.

5 degrees of freedom

physical adjustment.

Kinematic

mount

LED

Measurement axis

Fig. 4-43. Side view diagram of measurement setup in NMIA showing the LED mounted in the aluminium mount supported by a carriage having five degrees of freedom in

physical adjustment.

The LEDs were held in place by a cylindrical nylon spacer with two holes running

parallel to the centre of the cylinder, allowing the legs of the LED to pass through the

spacer. The spacer was held in place using a copper side spring as shown in Fig. 4-44.

Grey nylon

support for

electrical

connectors

aluminium

mount

LED

White nylon spacer

Copper spring

Current feed and

voltage sensing leads

Fig. 4-44. Top view, cross-section diagram of LED mount in NMIA, showing the nylon spacer located by the copper spring, and including the grey nylon mount via which

electrical connections were made.

The legs of the LED were inserted into a grey nylon mount containing four screw


92

tensioned gold contacts via which the LED current was supplied and the LED potential

was measured.

A temperature probe was attached to the aluminium base using aluminium tape

to provide reasonable thermal contact. This provided a cross-check on the LED base

temperature.

The detector system used was based on a calibrated Hamamatsu S6337

windowless silicon photodiode mounted behind a round 100 mm2 area polished steel

aperture with aperture lands at a 60 angle to the measurement axis. The area

surrounding the aperture was covered using a shield plate having a diffuse black

spectrally non-selective paint to reduce inter-reflection between the LED mount and the

aperture as shown in Fig. 4-45.

shutter

LED

Spectrometer Silicon

detector

Aperture

Black shield

plate

Optical fibre

Fig. 4-45. Diagram of the detection system with precision steel aperture masked by blackened cover, optical fibre fed spectrometer and shutter.

A small area shutter was placed between the LED and the detector aperture to

allow the stray light level to be recorded as far as possible. This was later subtracted

from the signal level.

The detector was mounted on an X-Y scanning stage with a resolution of 2 µm.

The detector was aligned with the LED centre by using a bench telescope with a ring

sight aligned along the measurement axis.

The separation between the tip of each LED and the plane of the detector

aperture was determined using a calibrated vernier mounted telescope with an optical

axis perpendicular to the measurement axis. The vernier resolution for this telescope was

0.01 mm.

The shutter did not restrict light entering the optical fibre and so the electronic

dark level (internal to the spectrometer) was used for the dark level of the spectrometer.

The optical fibre was aligned to point directly at the LED by finding the maximum signal.

For each LED the spatial uniformity of the irradiance output from the LED was


93

measured over approximately ± 20 mm around the central measurement position in

order to determine uncertainties due to spatial and angular variation.


The windowless silicon photo-diode used was calibrated for spectral responsivity against

NMIA reference silicon photo-diodes (report RN090120, dated 9 February 2009). The

reference silicon diodes were in turn calibrated directly against the NMIA primary

standard cryogenic radiometer at selected laser wavelengths as well as for relative

spectral response (reports RN45905, RN45906, RN45907, RN060931 and RN060932,

dated 8 May 2003, 9 May 2003, 9 May 2003, 25 Aug 2006 and 25 Aug 2006 respectively).

The spectrometer was calibrated using NMIA colour standard source FEL6. This

source was calibrated for relative spectral irradiance directly against a blackbody

(RN46736, dated 13 July 2004) at the same time, and using the same method, as for the

lamps NMIA used in the CCPR K1-a 2005 Spectral Irradiance Key Comparison. Further

details of the traceability of the relative spectral irradiance of lamp FEL6 can be found in

the final report of this comparison.


In this section, all indicated uncertainty values refer to the standard uncertainty unless

explicitly described otherwise. All uncertainty components have a sensitivity coefficient of

1 unless explicitly described otherwise.

The spatial distribution of the irradiance field in the plane at a distance of 100mm

from the tip of each LED was measured over a square area of approximately 40 mm ×

40 mm. The results were analysed and the largest gradient of irradiance within a 1 mm

distance of the centre of the scan was evaluated. This gradient was used in the

calculation of the uncertainty components for alignment, both angular and translational,

as follows.

The angular alignment of the mount was considered to have an uncertainty of

0.1°. The LED within the mount was estimated to contribute an uncertainty of between

0.1° and 0.2°, with the angular alignment of the aperture making a similar contribution.

To allow for all these angular uncertainties, a value of 0.5° was estimated for the

uncertainty of misalignment of the LED geometric axis to the measurement axis. At a

distance of 100 mm, this is approximately equivalent to a translational misalignment of

0.9 mm, which when multiplied by the gradient (as determined above) gave an estimate

of the uncertainty in irradiance due to any angular misalignment.


94

The translational alignment of the LED to the centre of the aperture, in the plane

perpendicular to the measurement axis, was estimated to be 1.0 mm. This was

multiplied by the gradient (as determined above) to give an estimate of the uncertainty

in irradiance due to any translational misalignment.

The feed current to the LED was determined by measuring the voltage drop

across a calibrated standard resistor in series with the LED. A standard allowance used by

NMIA for this measurement is 0.01%, which easily covers all our standard resistor /

digital voltmeter combinations. Each LED was measured at a range of current values

close to the target current value of 20 mA and a relationship between the LED optical

output and the LED current was empirically determined for each. The current sensitivity

values determined were used to calculate the luminous intensity of each LED at the

target current value. These sensitivity values were subsequently used in determineation

of the current related uncertainty component.

As described above, a white nylon support was placed immediately behind the

LED to hold it in place during measurement. An obvious glow from the nylon was visible

during measurements, and would thus be the main contributor to stray light for all LED’s

except the Diffused type (which have virtually zero emission in the backward direction).

Subsequent to the main tests, the nylon support was painted black and a variation of

approximately 1.6% in the optical output was observed. This was used as the uncertainty

component for stray light. Other factors that could potentially contribute to stray light

were considered to be negligible as the shutter used was of a minimal size and the

irradiance level with the shutter closed was measured as the background and subtracted

for all measurements.

The detector response to each LED was calculated using the pre-determined

spectral response of the detector and the measured spectrum of the LED. The

wavelength resolution of the system used to measure the LED was 0.4 nm. The

calculations of the detector response to each LED were performed with spectral

displacements of both +0.4 nm and -0.4 nm to determine the variation of detector

response. This produced variations in the derived values of between 0.7% and 1.5%, and

it was decided to use the worst case of 1.5% as an estimate of uncertainty due to

spectral mismatch for all cases.

Two other factors were considered with regard to the measurement of the

spectrum of the LED, but were finally considered negligible in comparison to the 1.5%

described above. Firstly the optical fibre feed was positioned approximately 30° from the

main measurement axis, with the resultant possibility that the recorded spectrum was


95

different from the on–axis spectrum. Separate tests were performed to measure the

variation in spectral content between the on axis and off axis measurements. Although

the differences were measurable, the cumulative effect was <0.5% in the value of the

calculated detector response. Secondly the stray light was not covered by subtraction of

a background level. However, other light sources were eliminated by the room being

dark, and stray light from undesirable reflections of the LED were most likely to have the

same or similar relative spectral content.

The traceable calibration of our detector for absolute spectral response has a

worst value of 0.4% (k = 2.0) over the whole visible range. Thus a value of 0.2% was

used as the estimate of uncertainty of the detector.

The measurement of Irradiance was performed by taking at least 30

measurements. The experimental standard deviation of the mean calculated from these

measurements (including measurements of the background ‘stray light’ levels) was used

as an estimate of the standard uncertainty and the degrees of freedom were estimated

to be 30.

The distance between the LED tip and the limiting aperture plane was able to be

set at 100.0 mm with an estimated uncertainty of 0.1 mm. Approximating the source to

be a point source meant an estimate of 0.1%, with a sensitivity coefficient of 2, could be

used as the uncertainty due to distance between the LED and the limiting aperture.

The limiting aperture used has an area close to 100.0 mm2 and has been calibrated with

an uncertainty of 0.25% (k = 2.0). Thus the standard uncertainty due to the area of the

limiting aperture was estimated to be 0.125%.

All measured photocurrents from the detector were within a 5:1 range of the

photocurrent measured when the detector was calibrated. A standard allowance of 0.01%

for this range of signal variation was used as the estimated uncertainty due to linearity of

the detector.

Table 4-72. NMIA uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Axis alignment, angular 0.9 B normal 1 0.9 100 X

Axis alignment,

translational

0.9 B normal 1 0.9 100 X


96

Current feeding accuracy 0.010 B normal 1.03 0.01 30 O

Stray light 0.46 B rectangular 1 0.46 100 O

Spectral mismatch

correction

0.43 B rectangular 1 0.43 100 O

Calibration of photometer 0.20 B normal 1 0.2 100 O

Reading repeatability 0.0045 A t 1 0.0045 30 X

Distance setting 0.10 B normal 2.0 0.2 100 O

Aperture Area 0.125 B normal 1 0.125 100 O

Non-linearity 0.010 B normal 1 0.10 100 O


rtainty (%)

-- -- normal -- 1.45 320 --

Table 4-73. NMIA uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


Axis alignment,

translational

0.5 B normal 1 0.5 100 X



Spectral mismatch

correction








rtainty (%)

-- -- normal -- 1.00 475 --


97

Table 4-74. NMIA uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


Axis alignment,

translational

0.6 B normal 1 0.6 100 X



Spectral mismatch

correction








rtainty (%)

-- -- normal -- 1.10 431 --

Table 4-75. NMIA uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


Axis alignment,

translational

0.08 B normal 1 0.08 100 X



Spectral mismatch

correction



98







rtainty (%)

-- -- normal -- 0.71 308 --

Table 4-76. NMIA uncertainty budget of averaged LED intensity measurement for diffuser-



ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


Axis alignment,

translational

0.08 B normal 1 0.08 100 X



Spectral mismatch

correction








rtainty (%)

-- -- normal -- 0.55 229 --

Table 4-77. NMIA uncertainty budget of junction voltage measurement.


99


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Calibration of voltmeter 0.001 B normal 1 0.001 100 O

Junction position

dependence

0.0035 B rectangular 1 0.0035 100 X

Reproducibility 0.0001 A normal 1 0.0001 30 X


rtainty (%)

-- -- normal -- 0.0036 116 --

4.12. NIST


The scale of Averaged LED Intensity at NIST is maintained on two non-diffuser type V(λ)-

corrected, silicon photodiode photometers having 100 mm2 circular apertures. The LED

photometers were calibrated at the NIST tunable-laser-based facility for Spectral

Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS)

described in Reference11. The LED photometers were calibrated for spectral irradiance

responsivity at distances of 100 mm and 316 mm using a sphere source that had a 5 mm

aperture. The spectral irradiance responsivity and the emitted LED spectrum measured in

the comparison APMP-S3c were used to calculate the illuminance responsivity of the LED

photometers.

The test LED was operated on DC power at a constant current of 20 mA using a

four-wire connection. The wiring diagram for this measurement is shown in Fig. 4-46. The

operating current of the LED was measured with an 8.5 digit multimeter. The test LED

was measured after it was powered on for 10 minutes. The output signal of the LED

photometer was simultaneously recorded with the LED current, LED voltage, LED ambient

temperature, room temperature, and room humidity. Each LED was measured for a total

of three lightings to check its reproducibility. The mean value of the three measurements

was reported, and the variation was included in the uncertainty budget of the

measurement. More details of the measurement facility and procedures are described in

11 Brown, S.W., Eppeldauer, G.P., and Lykke, K.R., NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources, Metrologia 37, 579-582. (2000)


100

Reference12.

Fig. 4-46. Wiring diagram for measurement of a test LED in NIST.


The LEDs were measured on the NIST 4 m photometry bench described in Reference13.

The two LED photometers were mounted on the rotation wheel with respect to the

reference plane of the carriage. A telescope was fixed on the side of the photometry

bench which imaged the front edge of the photometer which was 4.5 mm away from the

reference place of the photometers. The photometer carriage was moved 95.5 mm away

from the telescope reference plane along the rail system and locked in the position. The

front section of the photometer carriage was separated from the wheel. The LED was

mounted in the holder on the front section as shown in Fig. 4-47. By examining the LED

from the side through the telescope, the tip of the LED was translated to the point in

space, set parallel to the detector axis, and adjusted vertically as shown in Fig. 4-48. The

LED is then rotated 90 degrees on the horizontal plane and adjusted to remain in the

horizontal plane. This iterative process was continued until the LED was aligned with the

optical axis when completely rotated.

12 Miller C. C., and Ohno Y., Luminous Intensity Measurement of LEDs at NIST, in Proc. of 2nd CIE Expert Symposium on LED Measurement, 28-32. (2001) 13 Ohno Y. NIST Special Publication 250-37, Photometric Calibration. (1997)


101

Fig. 4-47. LED holder and photometer wheel on the NIST photometry bench.

Fig. 4-48. View in the telescope showing the LED tip aligned to the right position and the LED

mechanical axis aligned with the optical axis of the photometry bench.


The two LED photometers used to measure the illuminance of the LEDs at the specified

distances were calibrated for spectral irradiance responsivity in the NIST tuneable-laser-

based SIRCUS facility14. The calibration was done by direct comparison of the photometer

with two of the NIST trap detectors, which maintain the NIST spectral irradiance scale

and are periodically calibrated against the NIST Reference Cryogenic Radiometer -

Primary Optical Watt Radiometer (POWR).


The uncertainty budgets for measurement of Averaged LED Intensity of the red, green,

blue, white, and diffuser-type green LEDs are shown in the tables below, and the

uncertainty budget for measurement of junction voltage of the test LEDs is shown in

14 Brown, S.W., Eppeldauer, G.P., and Lykke, K.R., NIST facility for Spectral Irradiance and Radiance Responsivity Calibrations with Uniform Sources, Metrologia 37, 579-582. (2000)


102

Table 4-83. The NIST policy on uncertainty statements is described in Reference15.

Table 4-78. NIST uncertainty budget of averaged LED intensity measurement for red LEDs

(R).

Table 4-79. NIST uncertainty budget of averaged LED intensity measurement for green LEDs

(G).

15 B. N. Taylor, and C. E. Kuyatt, Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, NIST Technical Note 1297. (1993)


103

Table 4-80. NIST uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


104

Table 4-81. NIST uncertainty budget of averaged LED intensity measurement for white LEDs

(W).

Table 4-82. NIST uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


105

Table 4-83. NIST uncertainty budget of junction voltage measurement (typical).

4.13. VNIIOFI

Not submitted.

4.14. MKEH


The measurements were made on a photometer bench with the help of our standard

LED photometer (f1’=1.39; entrance aperture 1 cm2), Keithley 6485 electrometer,

alignment lasers, current generator for the LED (type adret 103), a 5 freedom LED holder

(two rotation + 3 translation) and an alignment system.

The photometer calibration is based on the spectral responsivity scale of MKEH.

Each LED spectral distribution was measured with the help of a spectral irradiance

comparator with 10 nW resolution in 1 nm steps. The photometer spectral responsivity

was measured in 1 nm steps as well.

Knowing the photometer responsivity at 555 nm, the entrance aperture, the

calculated mismatch correction factor for each LED, the measured photocurrent and the


106

distance we simply calculated the cd value for each LED.

The junction voltage was measured with 4 wire method with a Keithley 2000

multimeter. The junction voltage was measured for 6 digits. The junction voltage drifted

and its average value was different at each relighting of the LED. Compared to this

uncertainty all other parameter is negligible. We cannot give uncertainty about the

contact potential. We used the same type of clamp for both pole.

The LEDs were powered with a current generator (Type: adret 103). The current

generator was calibrated before the measurements at the Electricity Laboratory with an

uncertainty of 2*10-5.


We have used an adjustment system for LED-s capable for 3 axis translation, pitch and

rotation. We have used a laser which was centred and perpendicular to the detector and

tried to centre the LED and align it’s axis to the laser. First we tried a camera as it was

mentioned but we were not happy with the results. Therefore we tried to use a direct

visual method for the alignment. We found it better. The statistical uncertainty of the

alignment of the different LEDs was given in my uncertainty budget in % of measured cd.


All measurements are traceable to MKEH spectral responsivity and spectral irradiance

scale. The MKEH spectral irradiance scale is traceable to the NIST scale.


Tables in the following show the detailed uncertainty budgets of the CIE B averaged

luminous intensity measurement for the LEDs used in this APMP LED comparison.

The uncertainty budget of the measurements is similar than any other candela

realization error budget. We think it speaks for itself. The only difference, that in this case

the whole error budget was dominated by the alignment errors.

Two persons repeated the alignment 3-5 times for each diode and calculated the

cd value. The calculated relative standard deviation for each LEDs gives the standard

uncertainty of the alignment. This value includes the distance alignment; the centering

and the axis alignment together. (We do not think that it can be measured separately.)

The measured standard uncertainty of the alignment for each diode is given in the

following:

LED relative


107

standard uncertainty

R1 0,53%

R2 0,34%

R3

G1 0,44%

G2

G3 0,21%

B1 0,71%

B2 0,49%

B3 0,68%

W1 0,20%

W2 0,35%

W3 0,24%

D1 0,18%

D2 0,24%

These uncertainties are random and give the uncorrelated statistical uncertainty of the

diode alignment. There is other uncertainty component concerning to the distance

uncertainty.

Table 4-84. MKEH uncertainty budget of averaged LED intensity measurement for red LEDs

(R).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Photometer S555 calibration

accuracy


Spectral mismatch

correction


Photometer aperture area B rectangular 1 0.05 ∞ O

LED alignment

(angular+centering+distanc

e)

A normal 1 0.34 ~

0.53

∞ O

LED distance uncertainty B rectangular 1 0.20 X


rtainty (%)

-- -- normal -- 0.55-

0.68

∞ --

Table 4-85. MKEH uncertainty budget of averaged LED intensity measurement for green

LEDs (G).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


108


accuracy


Spectral mismatch

correction



LED alignment


e)

A normal 1 0.21 ~

0.44

∞ O



rtainty (%)

-- -- normal -- 0.45-

0.59

∞ --

Table 4-86. MKEH uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


accuracy


Spectral mismatch

correction



LED alignment


e)

A normal 1 0.49 ~

0.71

∞ O



rtainty (%)

-- -- normal -- 0,68-

0,85

∞ --

Table 4-87. MKEH uncertainty budget of averaged LED intensity measurement for white

LEDs (W).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


accuracy


Spectral mismatch

correction

B rectangular 1 0,20 ∞ X



109

LED alignment


e)

A normal 1 0.20 ~

0.35

∞ O



rtainty (%)

-- -- normal -- 0.47-

0.55

∞ --

Table 4-88. MKEH uncertainty budget of averaged LED intensity measurement for diffuser-



ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


accuracy


Spectral mismatch

correction



LED alignment


e)

A normal 1 0.18 ~

0.24

3-6 O



rtainty (%)

-- -- normal -- 0.46-

0.48

∞ --

Table 4-89 is the detailed uncertainty budget of the junction voltage measurement.

Table 4-89. MKEH uncertainty budget of junction voltage measurement (typical).


ncertainty

(%)

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Calibration of voltmeter 0.0003 B normal 1 0.0003 ∞ O

Junction position

dependence

N.A. B rectangular 1 N.A. ∞

Reproducibility 0.01-0.03 A normal 1 0.01-

0.03

5 X


rtainty (%)

-- -- normal -- 0.01-

0.03

--


110

4.15. INM


At INM-Ro the measurement set-up closely followed the CIE Technical Report 127:1997

recommendation. The measurement set up (Fig. 4-49) was mounted on a prismatic rail

providing axial positioning.

Fig. 4-49. Setup for average luminous intensity measurements in INM Romania.

A four wire technique as described in the APMP-PR-S3a comparison protocol was

used in order to (almost) simultaneously measure the current fed into the measured LED

and the junction voltage. The LED current was generated by a finely tuned voltage

stabilised supply and a current measurement shunt across which the voltage was

measured with a digital voltmeter. The LEDs junction voltage and was measured with a

similar digital voltmeter.

During the measurements, the photocurrent generated by the photometric head

was fed into Current to Voltage converter with a transimpedance factor of 1E6 V/A. The

output voltage was measured with a third digital voltmeter.

The INM photometer was equipped with a Hamamatsu S 1337-1010BQ which

window was replaced with an IR filter. A small integrating sphere of about 50 mm dia.


111

was mounted in front of the filtered photodiode. A screen was mounted inside of the

sphere in order to avoid direct irradiance. This sphere was provided with a precision

circular aperture (Fig. 4-49). The small sphere inner surface and the inner diffuser were

covered with a thick sprayed BaSO4 coating (about 25 sprayed layers, the last 4 without

binder).

The spectral densities of the standard lamp and of the LED under calibration were

measured with a fibre optic input spectrometer. The measurement of the spectral density

of the emitted flux was performed with a CCD spectrometer providing a (1 ± 0.1) nm

bandwidth. The spectrometer input fibre head was provided with a diffusing IR filter.


The measured LED was mounted in a cylindrical hole perpendicular on a black slab itself

attached to a cinematic mount. This arrangement provided adjustment with six degrees

of freedom (Fig. 4-49).

Prior to the LED mounting and measurement, a laser diode was mounted on the

prismatic rail instead of the photometric head. First, it was used to align the hole to the

measurement axis. Next, a small mirror was flushed to the black slab which position was

finely adjusted in order to reach the perpendicularity of the slab surface to the optical

axis of the rail. After adjusting the slab perpendicularity to the measurement axis, the

LED was mounted in the black cylindrical hole so that only it’s front part was visible (Fig.

4-49). The tip of the LED under calibration was brought in the same plane as the slab

surface so that the LED tip to the photometer precision aperture plane distance could be

adjusted using a calliper.


The photometer as a whole (including the photometric head, the current to voltage

converter and the associated multimeter) spectral responsivity was characterised against

an INM-RO spectral responsivity reference traceable to the LNE-INM primary reference

(cryogenic radiometer).

The spectrometer wavelength scale was calibrated against low pressure spectral

Hg, Cd and He lamps traceable to the INM reference for length measurements (stabilised

He-Ne laser). For all wavelengths within the visible range it was found to be accurate

within ±0.3 nm.

The spectrometer irradiance scale was calibrated against a irradiance spectral

density lamp, traceable to the MIKES–TKK reference. The spectrometer photometric

linearity was calibrated and further checked against a set of spectral transmittance filters


112

(neutral glass of NG type), traceable to the INM reference spectrophotometer.

All voltage measurements were traceable to the national references of Romania

(group of stabilised Zener diodes of Fluke 732 B). The shunt resistance used to generate

the feeding current was calibrated with traceability to the national references (group of

electrical resistors).

All dimensional measurements (distance and the diameter of the photometer

aperture) are traceable to the INM-RO national reference (stabilised He-Ne laser).

The temperature was measured with a digital thermometer calibrated with traceability to

the INM maintained SIT90 fixed points.


The expression of the LED average luminous intensity, avI , is:

)1(max.

2

54321 sp

ph

ph

av CKAs

IdCCCCCI

where: 1C is the feeding current factor; 2C is the ambient temperature correction

factor; 3C is the stray light coefficient factor; 4C is the tilting correction factor; 5C is

the centring correction factor; max.phs is the photometer maximum spectral responsivity;

d is the LED to the photometer aperture distance (Fig. 4-49); phI is the generated by

the pho-current; A is the photometer measurement aperture area; )(V is the

relative responsivity of the CIE standard observer; K is the luminous efficacy constant

(683 lm/W);

spC is the spectral correction factor:

)2(

)()(

)()(

830

380

.,

830

380

,

dsS

dVS

C

relphrled

rled

sp

where: )(. relphs is the photometer relative spectral responsivity; )(, rledS is the LED

relative spectral density and )(V is the relative efficacy of the CIE standard observer.

Tables in the following are the detailed uncertainty budgets of the CIE B averaged

luminous intensity measurement for the LEDs used in this APMP LED comparison.

Table 4-90. INM uncertainty budget of averaged LED intensity measurement for red LEDs (R).


113


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?

Feeding current factor 1C 0.001 B normal

avI 0.1 ∞ O

Ambient temperature

correction factor 2C

0.001 B rectangular avI 0.1 ∞ X

Stray light coefficiency

factor 3C

0.010 B rectangular avI 1.0 ∞ O

Tilting correction factor

4C


Centering correction factor

5C


Potometer maximum

spectral responsivity

max.phs

0.14

mA/W

B normal max./ phav sI

1.0 ∞ O

Photocurrent reading phI 0.01

phI B normal phav II /

1.0 ∞ O

Distance setting d 0.10 mm B rectangular dI av /2 0.1 ∞ O

Photometer aperture area

A

0.30 mm2 B normal AIav /

0.3 ∞ O

Spectral correction factor

spC

0.05 spC B normal avI 5.0 ∞ O

Repeatability 0.001avI A normal

avI 0.1 ∞ X


rtainty (%)

-- -- normal -- 5.4 ∞ --

Table 4-91. INM uncertainty budget of averaged LED intensity measurement for green LEDs

(G).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


avI 0.1 ∞ O

Ambient temperature




factor 3C



4C



114


5C


Potometer maximum


max.phs

0.14

mA/W


1.0 ∞ O



1.0 ∞ O



A


0.3 ∞ O


spC

0.05 spC B normal avI 4,5 ∞ O


avI 0.1 ∞ X


rtainty (%)

-- -- normal -- 4.8 ∞ --

Table 4-92. INM uncertainty budget of averaged LED intensity measurement for blue LEDs

(B).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


avI 0.1 ∞ O

Ambient temperature




factor 3C



4C



5C


Potometer maximum


max.phs

0.14

mA/W


1.0 ∞ O



1.0 ∞ O



A


0.3 ∞ O


spC



115


avI 0.1 ∞ X


rtainty (%)

-- -- normal -- 5.4 ∞ --

Table 4-93. INM uncertainty budget of averaged LED intensity measurement for white LEDs

(W).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


avI 0.1 ∞ O

Ambient temperature




factor 3C



4C



5C


Potometer maximum


max.phs

0.14

mA/W


1.0 ∞ O



1.0 ∞ O



A


0.3 ∞ O


spC



avI 0.1 ∞ X


rtainty (%)

-- -- normal -- 5.7 ∞ --

Table 4-94. INM uncertainty budget of averaged LED intensity measurement for diffuser-type

green LEDs (D).


ncertainty

Ty

pe

Probability

distributio

n

Sensitivity co

efficient

Contrib

ution

(%)

Deg. of

freedo

m

Correl

ated?


avI 0.1 ∞ O


116

Ambient temperature




factor 3C



4C



5C


Potometer maximum


max.phs

0.14

mA/W


1.0 ∞ O



1.0 ∞ O



A


0.3 ∞ O


spC



avI 0.1 ∞ X


rtainty (%)

-- -- normal -- 4.8 ∞ --

The junction voltage expression is:

readj VCCV 21

readV : the mean reading ; 1C : temperature factor and

2C : position factor


measurement.

Table 4-95. INM uncertainty budget of junction voltage measurement.


ncertainty

Ty

pe

Probability

distribution

Sensitivity

coefficient

Contribut

ion (%)

Deg.

of fre

edom

Correl

ated?

Mean reading readV 2E-5 V B normal 1 0.02 ∞ O

Temperature factor 1C 0.0010 B rectangular readV

0.10 ∞ X

Position factor 2C 0.0005 B rectangular readV

0.05 ∞ X


117

Repeatability 0.0005 jV

A normal 1 0.05 ∞ X


rtainty (%

-- -- normal -- 0.13 ∞ --


118

5. Reported Results of Participants

In this chapter, the results of the comparison S3a are presented, which are reported by

each participant as the final version, i.e., after the verification in the pre-draft A process.

We note that, throughout this report document, the uncertainty values with a symbol U

indicate the expanded uncertainties for a confidence level of 95 % normally with a

coverage factor of k = 2, while the values with a symbol u indicate the standard

uncertainties.

5.1. KRISS

As the pilot laboratory of the comparison, KRISS measured each LED at most three times:

the first measurement before sending the LEDs for the first round, the second after

receiving the LEDs from the first round, and the third after receiving the LEDs from the

second round. The final control measurement of the first round is also regarded as the

initial control measurement of the second round. Note that the artefact sets #4 and #8

are circulated only one round. The repeated measurements provide information on the

stability of the artefact LEDs, which will be discussed in Section 6.2.

Table 5-1 sumarizes the measurement results of KRISS of all the artefact LEDs. The

uncertainty values are not explicitly shown in this table but refered to the budgets in

Table 4-1 ~ Table 4-6. The laboratory conditions are kept at a temperature of (25 ± 2) ºC

and a relative humidity of (45 ± 15) %. The burning time of each measurement was 20

minutes in average.

Table 5-1. Measurement results of KRISS.

artifact

set LED

1. measurement 2. measurement 3. measurement

ILED (cd) Vj (V) ILED (cd) Vj (V) ILED (cd) Vj (V)

#1

R-1 0.7067 1.8846 0.7111 1.8870 0.7107 1.8856

R-2 0.6954 1.8881 0.7025 1.8918 0.6999 1.8889

R-3 0.6967 1.9212 0.7030 1.9245 0.7039 1.9217

G-1 2.6916 3.2972 2.6834 3.3016 2.6964 3.2964

G-2 2.5223 3.4378 2.5127 3.4424 2.5178 3.4350

G-3 2.6824 3.3151 2.6904 3.3201 2.6687 3.3139

B-1 0.8124 3.3764 0.8032 3.3791 0.8051 3.3744

B-2 0.8394 3.3773 0.8310 3.3830 0.8197 3.3758

B-3 0.8476 3.3469 0.8456 3.3522 0.8438 3.3438

W-1 0.6423 3.4455 0.6872 3.4474 0.6822 3.4399

W-2 0.6356 3.4651 0.6323 3.4664 0.6224 3.4569

W-3 0.7009 3.4194 0.6992 3.4203 0.6863 3.4109

D-1 0.0848 3.4759 0.0844 3.4767 0.0837 3.4709

D-2 0.0904 3.3135 0.0902 3.3154 0.0900 3.3117


119

#2

R-1 0.6795 1.8888 0.6856 1.8870 0.6944 1.8946

R-2 0.6855 1.8979 0.6905 1.8961 0.6981 1.9043

R-3 0.6996 1.9017 0.7083 1.9001 0.7143 1.9086

G-1 2.4467 3.4765 2.5733 3.4854 2.5856 3.4822

G-2 2.5335 3.3957 2.5322 3.4032 2.5485 3.4003

G-3 2.7702 3.3058 2.7863 3.3126 2.8055 3.3105

B-1 0.7669 3.4556 0.7560 3.4626 0.7630 3.4587

B-2 0.8380 3.3734 0.8306 3.3832 0.8344 3.3805

B-3 0.7736 3.3550 0.7698 3.3621 0.7741 3.3600

W-1 0.6715 3.3047 0.6786 3.3103 0.6753 3.3066

W-2 0.6863 3.4235 0.6875 3.4297 0.6857 3.4235

W-3 0.6173 3.4515 0.6183 3.4602 0.6147 3.4590

D-1 0.0892 3.4018 0.0890 3.4010 0.0880 3.3981

D-2 0.0743 3.4890 0.0738 3.4889 0.0733 3.4864

#3

R-1 0.7154 1.8955 0.6983 1.8908 0.7026 1.8894

R-2 0.7383 1.9004 0.7190 1.8941 0.7200 1.8930

R-3 0.7344 1.9046 0.7146 1.8987 0.7178 1.8976

G-1 2.7833 3.5277 2.7444 3.5122 2.7466 3.5093

G-2 2.5187 3.3920 2.5048 3.3793 2.4973 3.3759

G-3 2.4658 3.3525 2.4366 3.3396 2.4403 3.3365

B-1 0.8172 3.4479 0.8120 3.4359 0.8068 3.4336

B-2 0.8755 3.4351 0.8604 3.4234 0.8602 3.4212

B-3 0.7054 3.5334 0.6980 3.5183 0.6938 3.5159

W-1 0.6831 3.4552 0.6711 3.4410 0.6697 3.4407

W-2 0.6695 3.3567 0.6572 3.3427 0.6538 3.3428

W-3 0.6931 3.3237 0.6827 3.3116 0.6807 3.3103

D-1 0.0857 3.3294 0.0849 3.3176 0.0844 3.3173

D-2 0.0964 3.3298 0.0956 3.3190 0.0951 3.3184

#4

R-1 0.7335 1.9010 0.7229 1.8976

R-2 0.6829 1.8970 0.6746 1.8942

R-3 0.7061 1.8983 0.6979 1.8958

G-1 2.6564 3.5243 2.6238 3.5168

G-2 2.8201 3.3081 2.7930 3.3031

G-3 2.6927 3.3694 2.6636 3.3629

B-1 0.9329 3.4312 0.9182 3.4265

B-2 0.8038 3.4739 0.7942 3.4689

B-3 0.8905 3.4108 0.8769 3.4057

W-1 0.7076 3.4498 0.6897 3.4397

W-2 0.6977 3.3500 0.6846 3.3435

W-3 0.7112 3.4569 0.6991 3.4509

D-1 0.0636 3.3117 0.0631 3.3028

D-2 0.0887 3.4146 0.0879 3.4050

#5

R-1 0.6939 1.9190 0.6977 1.9189 0.6966 1.9193

R-2 0.7185 1.9230 0.7190 1.9229 0.7205 1.9238

R-3 0.6691 1.8858 0.6745 1.8864 0.6757 1.8866

G-1 2.6549 3.3126 2.6840 3.3131 2.6498 3.3141

G-2 2.4914 3.4478 2.4800 3.4494 2.4426 3.4509

G-3 2.5619 3.3808 2.5746 3.3829 2.5854 3.3843

B-1 0.7896 3.4134 0.8006 3.4155 0.7948 3.4140

B-2 0.8971 3.4154 0.9120 3.4175 0.9085 3.4160


120

B-3 0.9084 3.4279 0.9145 3.4307 0.9085 3.4334

W-1 0.6718 3.3232 0.6699 3.3180 0.6655 3.3152

W-2 0.7006 3.4495 0.7018 3.4458 0.6975 3.4417

W-3 0.6810 3.4551 0.6822 3.4530 0.6804 3.4546

D-1 0.0653 3.4818 0.0653 3.4939 0.0645 3.4959

D-2 0.0620 3.4911 0.0621 3.5051 0.0616 3.5046

#6

R-1 0.7000 1.8992 0.7136 1.9024 0.7108 1.9017

R-2 0.6563 1.8856 0.6635 1.8888 damaged

R-3 0.7023 1.8954 0.7144 1.8985 damaged

G-1 2.8398 3.2992 2.8575 3.3039 damaged

G-2 2.7226 3.3015 2.7450 3.3067 damaged

G-3 2.4871 3.3214 2.4902 3.3283 2.4712 3.3257

B-1 0.9185 3.4189 0.9231 3.4258 0.9130 3.4232

B-2 0.8098 3.3772 0.8125 3.3840 0.8037 3.3821

B-3 0.8244 3.3829 0.8236 3.3902 damaged

W-1 0.6933 3.4079 0.6739 3.4122 0.6714 3.4120

W-2 0.6828 3.4052 0.6709 3.4105 0.6651 3.4098

W-3 0.7091 3.4214 0.7016 3.4269 0.6949 3.4253

D-1 0.0935 3.3568 0.0937 3.3672 0.0933 3.3681

D-2 0.0706 3.4505 0.0707 3.4617 damaged

#7

R-1 0.6807 1.9220 0.6852 1.9209 0.6656 1.9179

R-2 0.7452 1.9040 0.7481 1.9033 0.7323 1.9000

R-3 0.6825 1.9200 0.6859 1.9198 0.6743 1.9167

G-1 2.7469 3.2989 2.7600 3.2980 2.7171 3.2912

G-2 2.6392 3.3643 2.6432 3.3626 2.6188 3.3549

G-3 2.8487 3.3041 2.8590 3.3021 2.8165 3.2955

B-1 0.8634 3.4653 0.8619 3.4638 0.8221 3.4545

B-2 0.8611 3.3991 0.8635 3.3972 0.8425 3.3888

B-3 0.8316 3.4295 0.8390 3.4271 0.8138 3.4187

W-1 0.6735 3.4753 0.6723 3.4746 0.6616 3.4608

W-2 0.6323 3.3643 0.6321 3.3620 0.6242 3.3521

W-3 0.6261 3.4177 0.6268 3.4145 0.6174 3.4045

D-1 0.0747 3.4555 0.0745 3.4500 0.0741 3.4435

D-2 0.0841 3.3811 0.0833 3.3766 0.0828 3.3721

#8

R-1 0.6941 1.8900 0.6945 1.8890

R-2 0.6875 1.8940 0.6850 1.8932

R-3 0.7175 1.8988 0.7180 1.8981

G-1 2.6454 3.5389 2.6504 3.5359

G-2 2.6749 3.2960 2.6693 3.2943

G-3 2.6376 3.2981 2.6278 3.2956

B-1 0.8573 3.4506 0.8567 3.4483

B-2 0.8583 3.3670 0.8621 3.3646

B-3 0.8428 3.4687 0.8433 3.4670

W-1 0.6586 3.4304 0.6569 3.4275

W-2 0.5997 3.4313 0.5965 3.4277

W-3 0.6224 3.4662 0.6195 3.4629

D-1 0.0871 3.3190 0.0867 3.3162

D-2 0.0913 3.3068 0.0912 3.3053


121

5.2. MIKES

MIKES of Finland measured the artifact set #1 in its first round from 07 April 2008 to 13

April 2008. The laboratory conditions are reported as temperature of (21.5 ± 1.0) ºC and

relative humidity of (31 ± 5) %. Table 5-2 shows the reported results of MIKES.

Table 5-2. Measurement results of MIKES.

artifact

set LED ILED (cd) U(ILED) (cd) Vj (V) U(Vj) (V)

burning

time (min)

#1

R-1 0.729 0.025 1.89426 0.00012 50

R-2 0.724 0.025 1.89866 0.00011 25

R-3 0.721 0.025 1.93310 0.00027 50

G-1 2.753 0.100 3.31595 0.00033 30

G-2 2.576 0.093 3.45713 0.00060 35

G-3 2.731 0.099 3.33517 0.00068 35

B-1 0.827 0.029 3.39520 0.00044 40

B-2 0.847 0.030 3.40018 0.00058 30

B-3 0.865 0.030 3.37001 0.00043 30

W-1 0.709 0.025 3.46899 0.00075 55

W-2 0.658 0.023 3.48621 0.00036 40

W-3 0.725 0.025 3.44078 0.00039 55

D-1 0.0872 0.0012 3.49373 0.00027 60

D-2 0.0926 0.0013 3.32914 0.00024 60

5.3. CMS-ITRI

CMS-ITRI of Chinese Taipei measured the artifact set #2 in its first round from 26 May

2008 to 28 May 2008. The laboratory conditions are reported as temperature of (23.0 ±

1.5) ºC and relative humidity of (45 ± 10) %. During the measurement at CMS-ITRI,

however, all the three red LEDs were damaged so that the red LEDs of the set #2 had to

be completely replaced for the second round. On the agreement of the other

participants, CMS-ITRI repeated the measurement of the new red LEDs of the set #2 in

Sept. ~ Oct. 2009. Table 5-3 shows the reported results of CMS-ITRI.

Table 5-3. Measurement results of CMS-ITRI.

artifact


burning

time (min)

#2

R-1 0.700 0.027 1.899 0.003 35

R-2 0.699 0.027 1.908 0.002 35

R-3 0.716 0.028 1.912 0.003 35

G-1 2.581 0.099 3.499 0.013 35

G-2 2.565 0.098 3.417 0.010 35

G-3 2.79 0.11 3.327 0.009 35

B-1 0.748 0.030 3.476 0.009 35


122

B-2 0.826 0.034 3.397 0.010 35

B-3 0.762 0.031 3.373 0.009 35

W-1 0.685 0.027 3.324 0.004 35

W-2 0.695 0.027 3.444 0.005 35

W-3 0.625 0.024 3.475 0.007 35

D-1 0.090 0.004 3.406 0.005 35

D-2 0.075 0.003 3.495 0.005 35

5.4. PTB

PTB of Germany measured the artifact set #3 in its first round from 16 June to 2 July

2008. The laboratory conditions are reported as temperature of (25.0 ± 0.7) ºC and

relative humidity of (50 ± 10) %. Table 5-4 shows the reported results of PTB.

Table 5-4. Measurement results of PTB.

artifact


burning

time (min)

#3

R-1 0.7226 0.0144 1.8945 0.0007 590

R-2 0.7324 0.0146 1.8976 0.0007 446

R-3 0.7394 0.0147 1.9024 0.0007 426

G-1 2.8081 0.0378 3.5230 0.0026 560

G-2 2.5521 0.0344 3.3894 0.0025 278

G-3 2.4880 0.0335 3.3503 0.0025 399

B-1 0.8139 0.0186 3.4455 0.0017 574

B-2 0.8516 0.0195 3.4338 0.0017 213

B-3 0.7097 0.0162 3.5314 0.0017 410

W-1 0.6912 0.0088 3.4509 0.0025 495

W-2 0.6789 0.0086 3.3525 0.0025 495

W-3 0.7064 0.0090 3.3217 0.0024 395

D-1 0.0860 0.0011 3.3177 0.0017 93

D-2 0.0973 0.0013 3.3182 0.0017 292

5.5. NMIJ

NMIJ of Japan measured the artifact set #4 in its first round from 17 April 2008 to 22

June 2008. The laboratory conditions are reported as temperature of (23 ± 2) ºC and

relative humidity of (50 ± 30) %. Table 5-5 shows the reported results of NMIJ.

Table 5-5. Measurement results of NMIJ.

artifact


burning

time (min)

#4

R-1 0.718 0.017 1.8984 0.0064 123

R-2 0.674 0.016 1.8966 0.0023 116

R-3 0.698 0.016 1.8976 0.0014 117

G-1 2.727 0.068 3.5180 0.0049 119


123

G-2 2.887 0.072 3.3045 0.0029 115

G-3 2.753 0.069 3.3644 0.0040 134

B-1 0.937 0.030 3.4275 0.0018 191

B-2 0.835 0.027 3.4713 0.0020 190

B-3 0.930 0.030 3.4075 0.0033 120

W-1 0.711 0.016 3.4424 0.0036 123

W-2 0.704 0.015 3.3478 0.0024 126

W-3 0.721 0.016 3.4544 0.0036 122

D-1 0.0652 0.0014 3.3021 0.0141 289

D-2 0.0909 0.0020 3.4051 0.0171 186

5.6. CENAM

CENAM of Mexico measured the artifact set #5 in its first round from 17 July 2008 to 21

July 2008. The laboratory conditions are reported as temperature of (22.7 ± 2.2) ºC and

relative humidity of (47.5 ± 8.0) %. Table 5-6 shows the reported results of CENAM.

Table 5-6. Measurement results of CENAM.

artifact


burning

time (min)

#5

R-1 0.4675 0.0248 1.9261 0.0010 56

R-2 0.4888 0.0278 1.9304 0.0008 48

R-3 0.4605 0.0263 1.8918 0.0006 45

G-1 2.3458 0.1702 3.3295 0.0013 47

G-2 2.2183 0.1480 3.4729 0.0020 51

G-3 2.3287 0.1423 3.4041 0.0014 46

B-1 0.7490 0.0429 3.4350 0.0014 48

B-2 0.8259 0.0508 3.4374 0.0012 47

B-3 0.8289 0.0512 3.4513 0.0013 52

W-1 0.5544 0.0315 3.3373 0.0013 59

W-2 0.5815 0.0345 3.4671 0.0011 47

W-3 0.5654 0.0306 3.4730 0.0018 45

D-1 0.0576 0.0037 3.5107 0.0016 51

D-2 0.0544 0.0037 3.5216 0.0013 54

5.7. LNE

LNE of France measured the artifact set #6 in its first round from 15 June 2008 to 13 July

2008. The laboratory conditions are reported as temperature of (22 ± 2) ºC and relative

humidity of (50 ± 10) %. Table 5-7 shows the reported results of LNE.

Table 5-7. Measurement results of LNE.

artifact


burning

time (min)

#6 R-1 0.745 0.015 1.90925 0.00057 120


124

R-2 0.692 0.014 1.89535 0.00057 120

R-3 0.750 0.015 1.90543 0.00057 120

G-1 2.985 0.057 3.31209 0.00066 120

G-2 2.861 0.054 3.31284 0.00066 120

G-3 2.603 0.049 3.33553 0.00067 120

B-1 0.934 0.028 3.43531 0.00069 120

B-2 0.816 0.024 3.39327 0.00068 120

B-3 0.825 0.025 3.39927 0.00068 120

W-1 0.709 0.011 3.41940 0.00068 120

W-2 0.702 0.011 3.42046 0.00068 120

W-3 0.731 0.011 3.43496 0.00069 120

D-1 0.0987 0.0018 3.37456 0.00067 75

D-2 0.0746 0.0013 3.46610 0.00069 75

5.8. METAS

METAS of Switzerland measured the artifact set #7 in its first round from 08 Sept. 2008

to 17 Sept. 2008. The laboratory conditions are reported as temperature of (25.0 ± 0.5)

ºC and relative humidity of (43 ± 5) %. Table 5-8 shows the reported results of METAS.

Table 5-8. Measurement results of METAS.

artifact


burning

time (min)

#7

R-1 0.6902 0.0095 1.9340 0.0082 290

R-2 0.7577 0.0109 1.9145 0.0082 101

R-3 0.6904 0.0096 1.9328 0.0082 103

G-1 2.8012 0.0483 3.3136 0.063 119

G-2 2.6865 0.0439 3.3798 0.063 82

G-3 2.9087 0.0484 3.3176 0.063 162

B-1 0.8823 0.0287 3.4816 0.075 135

B-2 0.8901 0.0302 3.4282 0.075 96

B-3 0.8471 0.0289 3.4464 0.075 104

W-1 0.6862 0.0091 3.4934 0.083 183

W-2 0.6414 0.0087 3.3792 0.083 88

W-3 0.6359 0.0090 3.4322 0.083 100

D-1 0.07577 0.00140 3.4599 0.063 139

D-2 0.08483 0.00156 3.3877 0.063 176

5.9. NMC-A*STAR

NMC-A*STAR of Singapore measured the artifact set #8 in its first round from 10 July

2008 to 28 August 2008. The laboratory conditions are reported as temperature of (23 ±

2) ºC and relative humidity of (60 ± 10) %. Table 5-9 shows the reported results of NMC-

A*STAR.


125

Table 5-9. Measurement results of NMC-A*STAR.

artifact


burning

time (min)

#8

R-1 0.713 0.016 1.8921 0.0022 76

R-2 0.702 0.015 1.8957 0.0022 57

R-3 0.735 0.016 1.9003 0.0022 54

G-1 2.678 0.051 3.5356 0.0024 60

G-2 2.701 0.051 3.2954 0.0024 59

G-3 2.648 0.050 3.2957 0.0024 45

B-1 0.865 0.019 3.4489 0.0025 65

B-2 0.873 0.019 3.3652 0.0025 44

B-3 0.856 0.019 3.4672 0.0025 45

W-1 0.666 0.012 3.4293 0.0041 65

W-2 0.604 0.011 3.4291 0.0041 58

W-3 0.627 0.011 3.4633 0.0041 52

D-1 0.0876 0.0018 3.3133 0.0021 43

D-2 0.0925 0.0018 3.3017 0.0021 57

5.10. VSL

VSL of the Netherlands measured the artifact set #1 in its second round from 13 October

2008 to 12 January 2009. The laboratory conditions are reported as temperature of (24.0

± 0.5) ºC and relative humidity of (45 ± 10) %. Table 5-10 shows the reported results of

VSL.

Table 5-10. Measurement results of VSL.

artifact


burning

time (min)

#1

R-1 0.728 0.011 1.8870 0.0031 115

R-2 0.711 0.012 1.8913 0.0031 108

R-3 0.717 0.010 1.9239 0.0031 166

G-1 2.746 0.049 3.2986 0.0056 353

G-2 2.586 0.039 3.4396 0.0059 462

G-3 2.745 0.057 3.3170 0.0054 358

B-1 0.814 0.012 3.3805 0.0055 146

B-2 0.833 0.012 3.3806 0.0058 143

B-3 0.852 0.016 3.3491 0.0055 310

W-1 0.698 0.008 3.4444 0.0057 135

W-2 0.644 0.013 3.4646 0.0059 133

W-3 0.712 0.018 3.4193 0.0059 176

D-1 0.0870 0.0014 3.4712 0.0056 38

D-2 0.0919 0.0025 3.3291 0.0115 90


126

5.11. NMIA16

NMIA of Australia measured the artifact set #2 in its second round from January 2009 to

May 2009. However, as the red LEDs of this set is replaced in the previous round of CMS-

ITRI, the three red LEDs are measured by NMIA as the first round. The laboratory

conditions are reported as temperature of (21.0 ± 0.5) ºC and relative humidity of (50 ±

10) %. Table 5-11 shows the reported results of NMIA.

Table 5-11. Measurement results of NMIA.

artifact


burning

time (min)

#2

R-1 0.793 0.023 1.90209 0.00014 2350

R-2 0.800 0.012 1.91198 0.00014 430

R-3 0.806 0.016 1.91743 0.00014 75

G-1 2.600 0.050 3.52445 0.00025 70

G-2 2.540 0.050 3.43681 0.00025 75

G-3 2.456 0.040 3.34151 0.00025 1010

B-1 0.729 0.016 3.49167 0.00025 310

B-2 0.813 0.018 3.41229 0.00025 70

B-3 0.737 0.014 3.38591 0.00025 105

W-1 0.729 0.010 3.34000 0.00025 155

W-2 0.745 0.010 3.46348 0.00025 70

W-3 0.662 0.009 3.49266 0.00025 965

D-1 0.0906 0.0010 3.43581 0.00025 75

D-2 0.0754 0.0009 3.52608 0.00025 195

5.12. NIST

NIST of the USA measured the artifact set #3 in its second round from 18 February 2009

to 25 February 2009. The laboratory conditions are reported as temperature of 25 ºC and

relative humidity of 17 %. Table 5-12 shows the reported results of NIST.

Table 5-12. Measurement results of NIST.

artifact


burning

time (min)

#3

R-1 0.728 0.018 1.889 0.005 60

R-2 0.741 0.018 1.892 0.005 80

R-3 0.746 0.018 1.896 0.005 80

G-1 2.898 0.076 3.504 0.009 80

G-2 2.599 0.068 3.374 0.008 60

G-3 2.541 0.067 3.332 0.008 60

16 The final version of the results of NMIA is received on 01 July 2010 after the review of uncertainty budgets in the pre-draft A process.


127

B-1 0.828 0.032 3.428 0.008 60

B-2 0.888 0.034 3.417 0.008 80

B-3 0.722 0.028 3.508 0.009 60

W-1 0.702 0.016 3.434 0.008 60

W-2 0.686 0.015 3.336 0.008 60

W-3 0.713 0.016 3.306 0.008 60

D-1 0.0898 0.0017 3.310 0.008 60

D-2 0.1007 0.0019 3.313 0.008 60

5.13. VNIIOFI

VNIIOFI of Russia measured the artifact set #5 in its second round from 28 November

2008 to 05 December 2008. The laboratory conditions are reported as temperature of

(22.0 ± 0.5) ºC and relative humidity of (62 ± 2) %. Table 5-13 shows the reported results

of VNIIOFI.

Table 5-13. Measurement results of VNIIOFI.

artifact


burning

time (min)

#5

R-1 0.7558 0.0027 1.933 0.001 82

R-2 0.7782 0.0063 1.938 0.001 70

R-3 0.7284 0.0043 1.898 0.001 70

G-1 2.6734 0.0211 3.341 0.001 72

G-2 2.3866 0.0515 3.483 0.001 83

G-3 2.5716 0.0404 3.412 0.001 74

B-1 0.7218 0.0106 3.443 0.001 73

B-2 0.8477 0.0147 3.445 0.001 70

B-3 0.8178 0.0180 3.460 0.001 70

W-1 0.6892 0.0038 3.346 0.001 69

W-2 0.7186 0.0025 3.477 0.001 69

W-3 0.7019 0.0025 3.486 0.001 71

D-1 0.0645 0.0002 3.514 0.002 189

D-2 0.0619 0.0004 3.525 0.002 117

5.14. MKEH

MKEH of Hungary measured the artifact set #6 in its second round from 20 November


(22.8 ± 0.8) ºC and relative humidity of (30 ± 10) %. Table 5-14 shows the reported

results of MKEH. Note that two LEDs (#5-R-3 and #5-G-2) are damaged during the

measurement in MKEH.

Table 5-14. Measurement results of MKEH.

artifact LED ILED (cd) U(ILED) (cd) Vj (V) U(Vj) (V) burning


128

set time (min)

#5

R-1 0.7211 0.0095 1.911 0.0011 90

R-2 0.6712 0.0069 1.898 0.0010 90

R-3 N.A. N.A. N.A. N.A. N.A.

G-1 2.6823 0.0298 3.319 0.0016 100

G-2 N.A. N.A. N.A. N.A. N.A.

G-3 2.5935 0.0209 3.3425 0.0008 80

B-1 0.9729 0.0162 3.442 0.0021 100

B-2 0.8645 0.0113 3.397 0.0016 80

B-3 0.8548 0.0137 3.401 0.0017 110

W-1 0.6944 0.0055 3.4245 0.0010 90

W-2 0.6908 0.0068 3.423 0.0006 70

W-3 0.7207 0.0060 3.439 0.0014 70

D-1 0.0970 0.0007 3.373 0.0011 60

D-2 0.0728 0.0006 3.471 0.0011 60

5.15. INM

INM of Romania measured the artifact set #7 in its second round from 13 December


(25.0 ± 0.2) ºC and relative humidity of (30 ± 5) %. Table 5-15 shows the reported results

of INM.

Table 5-15. Measurement results of INM.

artifact


burning

time (min)

#7

R-1 0.748 0.082 1.925 0.006 5

R-2 0.810 0.089 1.906 0.006 5

R-3 0.765 0.084 1.926 0.006 5

G-1 3.134 0.345 3.303 0.010 5

G-2 2.958 0.325 3.366 0.010 5

G-3 3.221 0.354 3.306 0.010 5

B-1 0.942 0.104 3.467 0.010 5

B-2 0.960 0.106 3.403 0.010 5

B-3 0.930 0.102 3.436 0.010 5

W-1 0.746 0.082 3.478 0.010 5

W-2 0.706 0.078 3.367 0.010 5

W-3 0.697 0.077 3.421 0.010 5

D-1 0.090 0.010 3.452 0.010 5

D-2 0.100 0.011 3.453 0.010 5


129

6. Pre-draft A Process

After the measurement process is completed, the preparation of the comparison report is

conducted according to the CCPR Guidelines. 17 The pre-draft A process consists of

verification of reported results, review of uncertainty budgets, and review of relative data.

In this chapter, we also describe the temperature-corrected results and the identification

of outliers.

6.1. Verification of Reported Results

The verification of reported results started in November 2009 after most of the

participants have submitted their results. The pilot sent to each participant the submitted

result values and the technical report including the uncertainty budgets. The participant

reviewed it to correct any error. After the participant confirmed the final version, no

correction is applied in the results and in the technical reports of the participants.

6.2. Temperature Correction and Artifact Drift

After the results are finalized by the verification, the pilot applied the temperature

correction based on the Eq. (3-1). By using the temperature sensitivity coefficients a, b,

and c of each LED and the measured junction voltages reported by the participants, all

the results could be converted to the values expected at the same junction voltage, i.e.,

at the same reference condition with a temperature of T0. We took the initial control

measurement of the pilot for each round as the reference condition for correction.

The tables below summarize the results before and after the temperature correction

for each measurement round. The relative differences of the participant’s results and of

the pilot’s results by the temperature correction are also calculated in the last two

columns to show the magnitudes of the correction. Note that the uncertainty of the

temperature correction was estimated to be 0.5 % as a relative standard uncertainty (see

Chapter 3), while all the participants claimed the uncertainty of the junction voltage

measurement much lower than this.

Table 6-1. Results of temperature correction for the round to MIKES.

artifact LED 1. meas.

of pilot

participant

lab

2. meas.

of pilot temperature corrected

relative

difference

relative

difference

17 CCPR Key Comparison Working Group, Guidelines for CCPR Comparison Report Preparation, Rev. 2 (Sept. 18, 2009), available at http://www.bipm.org/en/committees/cc/ccpr/publications_cc.html

http://www.bipm.org/en/committees/cc/ccpr/publications_cc.html


130

set IP1 (cd) IL (cd) IP2 (cd) IL* (cd) IP2

* (cd)

IL* - IL IP2

* – IP2

#1

R-1 0.7067 0.729 0.7111 0.7124 0.7070 -2.33% -0.57%

R-2 0.6954 0.724 0.7025 0.7049 0.6962 -2.71% -0.91%

R-3 0.6967 0.721 0.7030 0.7039 0.6982 -2.43% -0.69%

G-1 2.6916 2.753 2.6834 2.7294 2.6778 -0.87% -0.21%

G-2 2.5223 2.576 2.5127 2.5578 2.5084 -0.71% -0.17%

G-3 2.6824 2.731 2.6904 2.7076 2.6843 -0.86% -0.23%

B-1 0.8124 0.827 0.8032 0.8289 0.8034 0.23% 0.03%

B-2 0.8394 0.847 0.8310 0.8483 0.8311 0.15% 0.01%

B-3 0.8476 0.865 0.8456 0.8628 0.8451 -0.26% -0.07%

W-1 0.6423 0.709 0.6872 0.6986 0.6864 -1.50% -0.12%

W-2 0.6356 0.658 0.6323 0.6492 0.6318 -1.35% -0.08%

W-3 0.7009 0.725 0.6992 0.7157 0.6988 -1.30% -0.05%

D-1 0.0848 0.0872 0.0844 0.0868 0.0844 -0.47% -0.02%

D-2 0.0904 0.0926 0.0902 0.0921 0.0902 -0.53% -0.07%

Table 6-2. Results of temperature correction for the round to CMS-ITRI.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.

of pilot temperature corrected relative

difference

IL* - IL

relative

difference

IP2* – IP2 IP1 (cd) IL (cd) IP2 (cd) IL

* (cd) IP2

* (cd)

#2

R-1 0.6856 0.700 0.6944 0.6781 0.6804 -3.23% -2.05%

R-2 0.6905 0.699 0.6981 0.6781 0.6835 -3.08% -2.13%

R-3 0.7083 0.716 0.7143 0.6943 0.6986 -3.12% -2.25%

G-1 2.4467 2.581 2.5733 2.5591 2.5643 -0.85% -0.35%

G-2 2.5335 2.565 2.5322 2.5419 2.5236 -0.91% -0.34%

G-3 2.7702 2.790 2.7863 2.7578 2.7750 -1.17% -0.41%

B-1 0.7669 0.748 0.7560 0.7479 0.7557 -0.02% -0.05%

B-2 0.8380 0.826 0.8306 0.8221 0.8284 -0.47% -0.27%

B-3 0.7736 0.762 0.7698 0.7624 0.7695 0.06% -0.03%

W-1 0.6715 0.685 0.6786 0.6751 0.6756 -1.47% -0.45%

W-2 0.6863 0.695 0.6875 0.6849 0.6843 -1.48% -0.47%

W-3 0.6173 0.625 0.6183 0.6137 0.6138 -1.84% -0.72%

D-1 0.0892 0.090 0.0890 0.0899 0.0890 -0.15% 0.03%

D-2 0.0743 0.075 0.0738 0.0749 0.0738 -0.19% 0.00%

Table 6-3. Results of temperature correction for the round to PTB.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#3

R-1 0.7154 0.7226 0.6983 0.7248 0.7079 0.30% 1.36%

R-2 0.7383 0.7324 0.7190 0.7382 0.7318 0.79% 1.74%

R-3 0.7344 0.7394 0.7146 0.7432 0.7263 0.51% 1.60%

G-1 2.7833 2.8081 2.7444 2.8112 2.7598 0.11% 0.56%

G-2 2.5187 2.5521 2.5048 2.5503 2.5166 -0.07% 0.47%

G-3 2.4658 2.4880 2.4366 2.4859 2.4511 -0.08% 0.59%

B-1 0.8172 0.8139 0.8120 0.8132 0.8117 -0.09% -0.04%


131

B-2 0.8755 0.8516 0.8604 0.8502 0.8602 -0.16% -0.03%

B-3 0.7054 0.7097 0.6980 0.7085 0.6985 -0.17% 0.07%

W-1 0.6831 0.6912 0.6711 0.6933 0.6783 0.31% 1.06%

W-2 0.6695 0.6789 0.6572 0.6805 0.6639 0.24% 1.01%

W-3 0.6931 0.7064 0.6827 0.7072 0.6889 0.11% 0.91%

D-1 0.0857 0.0860 0.0849 0.0865 0.0853 0.55% 0.53%

D-2 0.0964 0.0973 0.0956 0.0979 0.0961 0.58% 0.49%

Table 6-4. Results of temperature correction for the round to NMIJ.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#4

R-1 0.7335 0.718 0.7229 0.7226 0.7293 0.67% 0.88%

R-2 0.6829 0.674 0.6746 0.6748 0.6799 0.11% 0.78%

R-3 0.7061 0.698 0.6979 0.6995 0.7029 0.19% 0.71%

G-1 2.6564 2.727 2.6238 2.7359 2.6305 0.32% 0.25%

G-2 2.8201 2.887 2.7930 2.8957 2.8006 0.30% 0.27%

G-3 2.6927 2.753 2.6636 2.7564 2.6718 0.12% 0.30%

B-1 0.9329 0.937 0.9182 0.9369 0.9180 -0.01% -0.02%

B-2 0.8038 0.835 0.7942 0.8349 0.7939 -0.02% -0.03%

B-3 0.8905 0.930 0.8769 0.9297 0.8764 -0.04% -0.06%

W-1 0.7076 0.711 0.6897 0.7148 0.6947 0.53% 0.72%

W-2 0.6977 0.704 0.6846 0.7047 0.6878 0.16% 0.47%

W-3 0.7112 0.721 0.6991 0.7220 0.7019 0.17% 0.40%

D-1 0.0636 0.0652 0.0631 0.0655 0.0634 0.50% 0.44%

D-2 0.0887 0.0909 0.0879 0.0912 0.0882 0.33% 0.34%

Table 6-5. Results of temperature correction for the round to CENAM.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#5

R-1 0.6939 0.4675 0.6977 0.4598 0.6978 -1.66% 0.01%

R-2 0.7185 0.4888 0.7190 0.4806 0.7190 -1.70% 0.00%

R-3 0.6691 0.4605 0.6745 0.4531 0.6733 -1.64% -0.17%

G-1 2.6549 2.3458 2.6840 2.3282 2.6834 -0.75% -0.02%

G-2 2.4914 2.2183 2.4800 2.1989 2.4784 -0.88% -0.06%

G-3 2.5619 2.3287 2.5746 2.3078 2.5721 -0.91% -0.10%

B-1 0.7896 0.7490 0.8006 0.7511 0.8006 0.29% 0.00%

B-2 0.8971 0.8259 0.9120 0.8270 0.9118 0.14% -0.02%

B-3 0.9084 0.8289 0.9145 0.8304 0.9143 0.19% -0.02%

W-1 0.6718 0.5544 0.6699 0.5488 0.6725 -1.02% 0.38%

W-2 0.7006 0.5815 0.7018 0.5750 0.7036 -1.14% 0.25%

W-3 0.6810 0.5654 0.6822 0.5586 0.6832 -1.21% 0.14%

D-1 0.0653 0.0576 0.0653 0.0571 0.0650 -0.89% -0.39%

D-2 0.0620 0.0544 0.0621 0.0539 0.0618 -0.97% -0.44%


132

Table 6-6. Results of temperature correction for the round to LNE.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#6

R-1 0.7000 0.745 0.7136 0.7257 0.7076 -2.66% -0.84%

R-2 0.6563 0.692 0.6635 0.6740 0.6575 -2.67% -0.91%

R-3 0.7023 0.750 0.7144 0.7298 0.7082 -2.77% -0.88%

G-1 2.8398 2.985 2.8575 2.9632 2.8493 -0.74% -0.29%

G-2 2.7226 2.861 2.7450 2.8443 2.7372 -0.59% -0.29%

G-3 2.4871 2.603 2.4902 2.5850 2.4814 -0.70% -0.35%

B-1 0.9185 0.934 0.9231 0.9337 0.9224 -0.03% -0.08%

B-2 0.8098 0.816 0.8125 0.8158 0.8116 -0.03% -0.11%

B-3 0.8244 0.825 0.8236 0.8251 0.8228 0.01% -0.09%

W-1 0.6933 0.709 0.6739 0.7026 0.6716 -0.91% -0.34%

W-2 0.6828 0.702 0.6709 0.6941 0.6680 -1.13% -0.43%

W-3 0.7091 0.731 0.7016 0.7236 0.6986 -1.02% -0.44%

D-1 0.0935 0.0987 0.0937 0.0980 0.0933 -0.67% -0.40%

D-2 0.0706 0.0746 0.0707 0.0742 0.0705 -0.53% -0.34%

Table 6-7. Results of temperature correction for the round to METAS.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#7

R-1 0.6807 0.6902 0.6852 0.6713 0.6870 -2.81% 0.26%

R-2 0.7452 0.7577 0.7481 0.7386 0.7494 -2.58% 0.18%

R-3 0.6825 0.6904 0.6859 0.6694 0.6864 -3.14% 0.07%

G-1 2.7469 2.8012 2.7600 2.7822 2.7613 -0.68% 0.05%

G-2 2.6392 2.6865 2.6432 2.6702 2.6451 -0.61% 0.07%

G-3 2.8487 2.9087 2.8590 2.8892 2.8621 -0.67% 0.11%

B-1 0.8634 0.8823 0.8619 0.8835 0.8619 0.13% 0.00%

B-2 0.8611 0.8901 0.8635 0.8938 0.8634 0.41% -0.01%

B-3 0.8316 0.8471 0.8390 0.8459 0.8393 -0.14% 0.03%

W-1 0.6735 0.6862 0.6723 0.6773 0.6726 -1.32% 0.05%

W-2 0.6323 0.6414 0.6321 0.6341 0.6332 -1.16% 0.18%

W-3 0.6261 0.6359 0.6268 0.6291 0.6284 -1.09% 0.25%

D-1 0.0747 0.07577 0.0745 0.0757 0.0747 -0.15% 0.19%

D-2 0.0841 0.08483 0.0833 0.0846 0.0835 -0.32% 0.22%

Table 6-8. Results of temperature correction for the round to NMC-A*STAR.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#8

R-1 0.6941 0.713 0.6945 0.7087 0.6965 -0.61% 0.29%

R-2 0.6875 0.702 0.6850 0.6984 0.6866 -0.52% 0.24%

R-3 0.7175 0.735 0.7180 0.7319 0.7195 -0.43% 0.20%

G-1 2.6454 2.678 2.6504 2.6811 2.6531 0.12% 0.10%


133

G-2 2.6749 2.701 2.6693 2.7020 2.6721 0.04% 0.11%

G-3 2.6376 2.648 2.6278 2.6518 2.6319 0.14% 0.15%

B-1 0.8573 0.865 0.8567 0.8651 0.8569 0.01% 0.02%

B-2 0.8583 0.873 0.8621 0.8732 0.8624 0.03% 0.04%

B-3 0.8428 0.856 0.8433 0.8560 0.8433 0.00% 0.01%

W-1 0.6586 0.666 0.6569 0.6666 0.6585 0.09% 0.25%

W-2 0.5997 0.604 0.5965 0.6050 0.5982 0.17% 0.27%

W-3 0.6224 0.627 0.6195 0.6285 0.6212 0.24% 0.28%

D-1 0.0871 0.0876 0.0867 0.0879 0.0868 0.31% 0.15%

D-2 0.0913 0.0925 0.0912 0.0927 0.0913 0.25% 0.07%

Table 6-9. Results of temperature correction for the round to VSL.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#1

R-1 0.7111 0.728 0.7107 0.7279 0.7131 -0.01% 0.33%

R-2 0.7025 0.711 0.6999 0.7118 0.7049 0.11% 0.71%

R-3 0.7030 0.717 0.7039 0.7179 0.7080 0.13% 0.58%

G-1 2.6834 2.746 2.6964 2.7499 2.7031 0.14% 0.25%

G-2 2.5127 2.586 2.5178 2.5887 2.5249 0.10% 0.28%

G-3 2.6904 2.745 2.6687 2.7489 2.6762 0.14% 0.28%

B-1 0.8032 0.814 0.8051 0.8141 0.8047 0.02% -0.05%

B-2 0.8310 0.833 0.8197 0.8329 0.8196 -0.01% -0.01%

B-3 0.8456 0.852 0.8438 0.8523 0.8448 0.04% 0.11%

W-1 0.6872 0.698 0.6822 0.6993 0.6854 0.19% 0.47%

W-2 0.6323 0.644 0.6224 0.6447 0.6258 0.11% 0.55%

W-3 0.6992 0.712 0.6863 0.7125 0.6904 0.06% 0.59%

D-1 0.0844 0.0870 0.0837 0.0871 0.0839 0.15% 0.16%

D-2 0.0902 0.0919 0.0900 0.0915 0.0901 -0.46% 0.13%

Table 6-10. Results of temperature correction for the round to NMIA.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#2

R-1 0.6795 0.793 0.6856 0.7660 0.6890 -3.53% 0.50%

R-2 0.6855 0.800 0.6905 0.7722 0.6938 -3.60% 0.48%

R-3 0.6996 0.806 0.7083 0.7745 0.7114 -4.07% 0.44%

G-1 2.5733 2.600 2.5856 2.5659 2.5889 -1.33% 0.13%

G-2 2.5322 2.540 2.5485 2.5079 2.5517 -1.28% 0.13%

G-3 2.7863 2.456 2.8055 2.4216 2.8090 -1.42% 0.12%

B-1 0.7560 0.729 0.7630 0.7305 0.7632 0.20% 0.02%

B-2 0.8306 0.813 0.8344 0.8108 0.8349 -0.27% 0.06%

B-3 0.7698 0.737 0.7741 0.7395 0.7741 0.34% 0.00%

W-1 0.6786 0.729 0.6753 0.7140 0.6773 -2.10% 0.30%

W-2 0.6875 0.745 0.6857 0.7285 0.6889 -2.27% 0.46%

W-3 0.6183 0.662 0.6147 0.6468 0.6153 -2.35% 0.10%

D-1 0.0890 0.0906 0.0880 0.0895 0.0881 -1.20% 0.10%


134

D-2 0.0738 0.0754 0.0733 0.0745 0.0733 -1.15% 0.08%

Table 6-11. Results of temperature correction for the round to NIST.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#3

R-1 0.6983 0.728 0.7026 0.7319 0.7054 0.53% 0.40%

R-2 0.7190 0.741 0.7200 0.7454 0.7223 0.60% 0.32%

R-3 0.7146 0.746 0.7178 0.7517 0.7199 0.76% 0.30%

G-1 2.7444 2.898 2.7466 2.9070 2.7496 0.31% 0.11%

G-2 2.5048 2.599 2.4973 2.6045 2.5007 0.21% 0.13%

G-3 2.4366 2.541 2.4403 2.5506 2.4441 0.38% 0.15%

B-1 0.8120 0.828 0.8068 0.8283 0.8068 0.04% 0.00%

B-2 0.8604 0.888 0.8602 0.8884 0.8603 0.04% 0.01%

B-3 0.6980 0.722 0.6938 0.7228 0.6939 0.11% 0.02%

W-1 0.6711 0.702 0.6697 0.7059 0.6698 0.55% 0.02%

W-2 0.6572 0.686 0.6538 0.6895 0.6538 0.50% -0.01%

W-3 0.6827 0.713 0.6807 0.7161 0.6814 0.44% 0.10%

D-1 0.0849 0.0898 0.0844 0.0901 0.0844 0.35% 0.01%

D-2 0.0956 0.1007 0.0951 0.1010 0.0951 0.28% 0.03%

Table 6-12. Results of temperature correction for the round to VNIIOFI.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#5

R-1 0.6977 0.7558 0.6966 0.7318 0.6961 -3.27% -0.08%

R-2 0.7190 0.7782 0.7205 0.7524 0.7191 -3.42% -0.19%

R-3 0.6745 0.7284 0.6757 0.7061 0.6752 -3.16% -0.07%

G-1 2.6840 2.6734 2.6498 2.6427 2.6485 -1.16% -0.05%

G-2 2.4800 2.3866 2.4426 2.3600 2.4412 -1.13% -0.06%

G-3 2.5746 2.5716 2.5854 2.5445 2.5839 -1.06% -0.06%

B-1 0.8006 0.7218 0.7948 0.7254 0.7948 0.50% 0.00%

B-2 0.9120 0.8477 0.9085 0.8506 0.9087 0.35% 0.01%

B-3 0.9145 0.8178 0.9085 0.8212 0.9085 0.41% 0.00%

W-1 0.6699 0.6892 0.6655 0.6756 0.6669 -2.01% 0.21%

W-2 0.7018 0.7186 0.6975 0.7044 0.6994 -2.02% 0.27%

W-3 0.6822 0.7019 0.6804 0.6869 0.6796 -2.18% -0.11%

D-1 0.0653 0.0645 0.0645 0.0641 0.0644 -0.62% -0.06%

D-2 0.0621 0.0619 0.0616 0.0615 0.0616 -0.60% 0.01%

Table 6-13. Results of temperature correction for the round to MKEH.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#6 R-1 0.7136 0.7211 0.7108 0.7051 0.7121 -2.26% 0.18%


135

R-2 0.6635 0.6712 N.A. 0.6547 N.A. -2.52% N.A.

R-3 0.7144 N.A. N.A. N.A. N.A. N.A. N.A.

G-1 2.8575 2.6823 N.A. 2.6614 N.A. -0.78% N.A.

G-2 2.7450 N.A. N.A. N.A. N.A. N.A. N.A.

G-3 2.4902 2.5935 2.4712 2.5765 2.4744 -0.66% 0.13%

B-1 0.9231 0.9729 0.9130 0.9739 0.9132 0.10% 0.02%

B-2 0.8125 0.8645 0.8037 0.8661 0.8038 0.18% 0.01%

B-3 0.8236 0.8548 N.A. 0.8554 N.A. 0.07% N.A.

W-1 0.6739 0.6944 0.6714 0.6879 0.6715 -0.94% 0.02%

W-2 0.6709 0.6908 0.6651 0.6844 0.6655 -0.94% 0.06%

W-3 0.7016 0.7207 0.6949 0.7143 0.6958 -0.90% 0.13%

D-1 0.0937 0.0970 0.0933 0.0968 0.0933 -0.22% -0.04%

D-2 0.0707 0.0728 N.A. 0.0726 N.A. -0.27% N.A.

Table 6-14. Results of temperature correction for the round to INM.

artifact

set LED

1. meas.

of pilot

participant

lab

2. meas.


difference

IL* - IL

relative

difference


* (cd) IP2

* (cd)

#7

R-1 0.6852 0.748 0.6656 0.7406 0.6707 -1.00% 0.76%

R-2 0.7481 0.810 0.7323 0.8045 0.7389 -0.69% 0.90%

R-3 0.6859 0.765 0.6743 0.7531 0.6798 -1.58% 0.80%

G-1 2.7600 3.134 2.7171 3.1262 2.7271 -0.25% 0.37%

G-2 2.6432 2.958 2.6188 2.9537 2.6283 -0.15% 0.36%

G-3 2.8590 3.221 2.8165 3.2142 2.8275 -0.21% 0.39%

B-1 0.8619 0.942 0.8221 0.9421 0.8223 0.01% 0.02%

B-2 0.8635 0.960 0.8425 0.9603 0.8428 0.03% 0.03%

B-3 0.8390 0.930 0.8138 0.9290 0.8151 -0.11% 0.16%

W-1 0.6723 0.746 0.6616 0.7441 0.6691 -0.26% 1.12%

W-2 0.6321 0.706 0.6242 0.7032 0.6295 -0.40% 0.83%

W-3 0.6268 0.697 0.6174 0.6935 0.6226 -0.50% 0.83%

D-1 0.0745 0.090 0.0741 0.0899 0.0742 -0.07% 0.23%

D-2 0.0833 0.100 0.0828 0.0965 0.0830 -3.60% 0.23%

Based on the temperature-corrected results of the pilot, the drift of the artifact LEDs

could be analyzed. Each LED is measured by the pilot two or three times depending on

the measurement rounds. The relative changes of the averaged LED intensity measured

by the pilot for each artifact LED are shown in the following figures, separated to a plot

without temperature correction and to a plot after correction. They show that the effect

of the temperature correction is small because the laboratory condition of the pilot was

little changed during the comparison. The most of the artifact LEDs show a drift smaller

than ±1 % for each round that is comparable to the measurement uncertainty of the

pilot. However, a few LEDs underwent a large drift and should be excluded from the data

analysis. The exclusion of the non-stable artifact LEDs is decided by the participant


136

through the procedure of review of relative data.

Fig. 6-1. Drift of the artefact set #1.




137





138



6.3. Review of Relative Data

The review of relative data started in December 2009. The pilot sent to the participants a

document with the relative data of each participant, which are the data reduced to check

only the stability of the artifact LEDs and the internal consistency of each participant. The

document circulated for the review of relative data is included in Appendix B: Review of

Relative Data as an electronic file. Note that both the uncorrected and temperature-

corrected data are separately presented.

The review comments of the participants are collected by the pilot and their

summary is included in Appendix C: Comments from Review of Relative Data. As a result

of the review of relative data, the data of the following artifact LEDs will be excluded

from the analysis on request of the participants and also due to damages during a

comparison round.

- #1-W-1 measured by MIKES (large drift)

- #2-G-1 measured by CMS-ITRI (large drift)

- #4-B-1/B-3/W-1 measured by NMIJ (large drift)


139

- #6-R-2/R-3/G-1/G-2/B-3/D-2 measured by MKEH (damage)

- #7-B-1 measured by INM (large drift)

6.4. Review of Uncertainty Budgets

The review of relative data started in March 2010 and completed in June 2010. The pilot

summarized the technical reports and uncertainty budgets of the participants to one

document and sent it to all the participants. We note that two participants, NMIA and

VNIIOFI, could not participate to the review process because their submission of the

technical report was delayed for NMIA and abandoned for VNIIOFI. The discussion

among the participants and the revisions of the budgets are conducted according to the

CCPR Guidelines. The review comments of the participants are collected by the pilot and

their summary is included in Appendix D: Comments from Review of Uncertainty Budgets.

The final version of the uncertainty budgets is summarized in Chapter 4.

6.5. Identification of Outliers

For the identification of outliers that can significantly skew the reference value of the

comparison, the pilot prepared a document with the relative deviation data of each

participant from the simple mean values of all the participants without disclosing the

participant’s identity and the absolute results. The document sent to the participant in

June 2010 is included in Appendix E: Identification of Outliers. As a result of the

discussion, it was agreed in September 2010 that the data with a relative deviation of

more than ±10 % from the mean are to identify as outliers. As the measurements of

each type (color) of LEDs are taken as each separate comparison, the outlier will be

excluded only from the analysis for the related LED type.


140

7. Data Analysis

The data analysis is performed based on the example in Appendix B of the CCPR

Guidelines.18 The only difference was the sequence of each round: “pilot – participant –

pilot” in the LED comparison, while “participant – pilot – participant” in the example of

the Guidelines. In this chapter, the equations of each analysis step are described. The

complete data of the calculation is included as an electronic file (Excel spreadsheet) at

the end of the chapter. Note that the analysis is repeated for each type of LEDs, and also

for the data without and with the temperature-correction.

7.1. Calculation of Difference to Pilot

For each participant with index i and for each LED with index j, the two measurement

results of the pilot (index P), before (index P1) and after (index P2) the participant, are

averaged by

1 2

, , ,

1

2

P P P

i j i j i jI I I . (7-1)

The relative standard uncertainty of the pilot’s average value Ii,jP is calculated from the

relative standard uncertainty ur,corP of the correlated components (scale uncertainty) and

the relative standard uncertainty ur,ucP of the uncorrelated components (transfer

uncertainty) according to

2

2 2

, , ,21

1( )

2

P P Pk

r i j r cor r uc

k

u I u u

. (7-2)

The values of ur,corP and ur,uc

Pk are determined by combing the related components in the

reported uncertainty budgets of the pilot in Table 4-1 ~ Table 4-5. Note that the pilot

reported and applied the upper boundary values for all the uncertainty components in

the budgets so that the relative standard uncertainty of each measurement remained the

same for each LED type.

The relative difference Δi,j between the participant i and the pilot (index P) for each

LED j is then calculated by

,

,

,

1i j

i j P

i j

I

I (7-3)

and its uncertainty by

2 22

, , , , ,( ) P

i j r i j r uc r add i ju u I u u I . (7-4)

18 CCPR Key Comparison Working Group, Guidelines for CCPR Comparison Report Preparation, Rev. 2 (Sept. 18, 2009), available at http://www.bipm.org/en/committees/cc/ccpr/publications_cc.html

http://www.bipm.org/en/committees/cc/ccpr/publications_cc.html


141

Here, ur,add(Ii,j) denotes the additional uncertainty in the measurement of LED j by the

participant i due to non-ideal characteristics of the artifact LEDs. For the results without

temperature correction, we used the drift of the LED for the corresponding round as the

value of ur,add(Ii,j), which is calculated from the relative difference of the two measurement

results of the pilot. For the results with temperature correction, the relative standard

uncertainty of the correction procedure of 0.5 % is additionally combined to ur,add(Ii,j). The

relative standard uncertainty of the participant ur(Ii,j) is determined from the reported

expanded results in Chapter 5.

Finally, the results of the multiple LEDs for each type are averaged for the participant

i by

,

1

3i i j

j

. (7-5)

Under assumption that the results of multiple LEDs measured by the same participant are

strongly correlated, the uncertainty of the relative differences is calculated simply by

,

1

3i i j

j

u u . (7-6)

For the pilot, we use now the index i = 0 and set Δ0 = 0. According to Eq. (7-4), the

uncertainty u(Δ0) for the pilot is the same as the total relative standard uncertainty

averaged over all the measurements by the pilot. For case of the temperature corrected

results, we added also the uncertainty of the correction to u(Δ0).

7.2. Calculation of Comparison Reference Value

The Reference Value (RV) of the comparison for each LED type is calculated using

weighted mean with cut-off. The cut-off value ucut is calculated by

for ; 0,...,cut r i r i r iu average u I u I median u I i N . (7-7)

Note that the outliers are not included in the calculation of the RV so that the number N

denotes the number of the participants whose comparison results are not identified as

outliers (the pilot not counted as a participant here).

The total relative standard uncertainty ur(Ii) of each participant i, averaged over LEDs

with different j, is adjusted by the cut-off (i = 0, …, N):

,

,

for

otherwise

r adj i r i r i cut

r adj i cut

u I u I u I u

u I u

(7-8)

Also, the uncertainty of Δi is adjusted after cut-off by

2 2

,adj i r adj i T iu u I u . (7-9)


142

Here, uT(Δi) denotes the transfer uncertainty component in u(Δi), which is separated by

2 2

T i i r iu u u I . (7-10)

These uncertainties are used to calculate the weights wi for each participant i given by

2

2

0

adj i

i N

adj i

i

uw

u

. (7-11)

Finally, the RV is determined by

0

N

RV i i

i

w

. (7-12)

The uncertainty of the comparison RV is given by

2

40

2

0

Ni

i adj i

RV N

adj i

i

u

uu

u

. (7-13)

7.3. Calculation of Degree of Equivalence

The unilateral degree of equivalence (DoE) of the participant i is defined by

i i RVD . (7-14)

The DoE is calculated according to Eq. (7-13) also for the participants whose comparison

results are identified as outliers. However, the uncertainty of DoE is different. For the

participants whose results are included in the calculation of the RV, the uncertainty of

DoE is given, as an expanded uncertainty with a coverage factor k = 2, by

2

2 2 2

20

2N

i

i i RV adj i

iadj i

uU k u u u

u

. (7-15)

For the participants whose results are excluded in the calculation of the RV, the

uncertainty of DoE is simplified to

2 2

i i RVU k u u . (7-16)

7.4. Data Analysis Spreadsheet

The Excel-file can be opened by a double-click on the icon below.

DoE_intensity_rev.xlsx


143

8. Comparison Results

8.1. Red LEDs

The comparison RV for averaged LED intensity of red LEDs is calculated to be

0.02292, 0.80% ( 2)RV rU k

for the results without temperature correction, and

0.01091, 0.84% ( 2)RV rU k

for the results after temperature correction. Table 8-1

and Table 8-2 summarize the comparison results for red LEDs without and with

temperature correction, respectively. The last column of each table shows the En criteria

of each participant, which is defined as the absolute ratio of Di and U(Di). Note that the

results of CENAM and NMIA are identified as outliers and not included in the calculation

of the RV.

Table 8-1. Comparison results for red LEDs without temperature correction.

participant Δi u(Δi) wi Di U(Di) En

MIKES 0.03151 2.06% 0.03960 0.009 0.040 0.225

CMS-ITRI 0.00929 2.40% 0.02933 -0.014 0.047 0.298

PTB 0.01596 2.90% 0.02007 -0.007 0.057 0.123

NMIJ -0.00891 1.96% 0.04403 -0.032 0.038 0.842

CENAM -0.32086 2.98% N.A. -0.344 0.060 5.733

LNE 0.05384 2.10% 0.03832 0.031 0.041 0.756

METAS 0.01149 1.26% 0.10168 -0.011 0.024 0.458

NMC-

A*STAR 0.02462 1.43% 0.08192 0.002 0.027 0.074

VSL 0.01912 1.21% 0.11592 -0.004 0.023 0.174

NMIA 0.15655 1.72% N.A. 0.134 0.035 3.829

NIST 0.03693 1.58% 0.06753 0.014 0.030 0.467

VNIIOFI 0.08143 0.97% 0.11827 0.059 0.019 3.105

MKEH 0.01255 1.19% 0.10954 -0.010 0.022 0.455

INM 0.10887 6.00% 0.00468 0.086 0.120 0.717

KRISS 0.00000 0.86% 0.22911 -0.023 0.015 1.533

Table 8-2. Comparison results for red LEDs after temperature correction.


MIKES 0.01006 1.98% 0.04708 -0.001 0.039 0.026

CMS-ITRI -0.01104 2.49% 0.02973 -0.022 0.049 0.449

PTB 0.01346 1.76% 0.05980 0.003 0.034 0.088

NMIJ -0.00961 1.64% 0.06896 -0.021 0.032 0.656

CENAM -0.33182 3.05% N.A. -0.343 0.062 5.532

LNE 0.03061 1.66% 0.06715 0.020 0.032 0.625

METAS -0.01732 1.44% 0.08511 -0.028 0.028 1.000

NMC-

A*STAR 0.01811 1.53% 0.07883 0.007 0.029 0.241


144

VSL 0.01713 1.38% 0.09624 0.006 0.026 0.231

NMIA 0.11230 2.11% N.A. 0.101 0.043 2.349

NIST 0.04173 1.77% 0.05923 0.031 0.034 0.912

VNIIOFI 0.04763 1.09% 0.10799 0.037 0.021 1.762

MKEH -0.01077 1.25% 0.10717 -0.022 0.024 0.917

INM 0.09245 5.84% 0.00542 0.082 0.116 0.707

KRISS 0.00000 0.99% 0.18728 -0.011 0.018 0.611

The DoEs and its uncertainties for red LEDs are plotted in Fig. 8-1 as dot symbols

and error bars, respectively. The red lines indicate the expanded relative uncertainty of

the comparison RV.


145

Fig. 8-1. DoE for red LEDs without and with temperature correction.

8.2. Green LEDs

The comparison RV for averaged LED intensity of green LEDs is calculated to be

0.01408, 0.76% ( 2)RV rU k


0.01174, 0.80% ( 2)RV rU k

for the results after temperature correction. Table

8-3 and Table 8-4 summarize the comparison results for green LEDs without and with




146

results of CENAM and INM are identified as outliers and not included in the calculation

of the RV.

Table 8-3. Comparison results for green LEDs without temperature correction.


MIKES 0.02140 1.96% 0.03875 0.007 0.038 0.184

CMS-ITRI 0.00846 2.16% 0.03172 -0.006 0.043 0.140

PTB 0.01569 1.54% 0.05974 0.002 0.030 0.067

NMIJ 0.02985 1.87% 0.04243 0.016 0.037 0.432

CENAM -0.10736 3.53% N.A. -0.121 0.071 1.704

LNE 0.04678 1.41% 0.07451 0.033 0.027 1.222

METAS 0.01791 1.25% 0.09450 0.004 0.024 0.167

NMC-

A*STAR 0.00933 1.31% 0.08664 -0.005 0.025 0.200

VSL 0.02447 1.36% 0.08058 0.010 0.026 0.385

NMIA -0.03792 1.40% 0.07540 -0.052 0.027 1.926

NIST 0.04558 1.58% 0.05920 0.032 0.031 1.032

VNIIOFI -0.01040 1.62% 0.05609 -0.024 0.032 0.750

MKEH 0.04547 1.22% 0.07834 0.031 0.024 1.292

INM 0.13459 5.73% N.A. 0.121 0.115 1.052

KRISS 0.00000 0.82% 0.22211 -0.014 0.014 1.000

Table 8-4. Comparison results for green LEDs after temperature correction.


MIKES 0.01418 2.05% 0.03986 0.002 0.040 0.050

CMS-ITRI -0.00002 2.22% 0.03402 -0.012 0.044 0.273

PTB 0.01282 1.34% 0.08598 0.001 0.026 0.038

NMIJ 0.03100 1.79% 0.05210 0.019 0.035 0.543

CENAM -0.11460 3.58% N.A. -0.126 0.072 1.750

LNE 0.04139 1.43% 0.08172 0.030 0.027 1.111

METAS 0.01088 1.37% 0.08903 -0.001 0.026 0.038

NMC-

A*STAR 0.00972 1.39% 0.08663 -0.002 0.027 0.074

VSL 0.02441 1.47% 0.07803 0.013 0.028 0.464

NMIA -0.05123 1.55% 0.06967 -0.063 0.030 2.100

NIST 0.04803 1.66% 0.06081 0.036 0.032 1.125

VNIIOFI -0.02107 1.73% 0.05569 -0.033 0.034 0.971

MKEH 0.03797 1.25% 0.08369 0.026 0.024 1.083

INM 0.13019 5.69% N.A. 0.118 0.114 1.035

KRISS 0.00000 0.96% 0.18276 -0.012 0.017 0.706

The DoEs and its uncertainties for green LEDs are plotted in Fig. 8-2 as dot symbols


the comparison RV.


147

Fig. 8-2. DoE for green LEDs without and with temperature correction.

8.3. Blue LEDs

The comparison RV for averaged LED intensity of blue LEDs is calculated to be

0.00139, 0.86% ( 2)RV rU k


0.00035, 0.92% ( 2)RV rU k


8-5 and Table 8-6 summarize the comparison results for blue LEDs without and with




148

results of INM are identified as outliers and not included in the calculation of the RV.

Table 8-5. Comparison results for blue LEDs without temperature correction.


MIKES 0.01988 2.07% 0.04539 0.021 0.040 0.525

CMS-ITRI -0.01338 2.42% 0.03319 -0.012 0.048 0.250

PTB -0.00280 1.86% 0.05641 -0.001 0.036 0.028

NMIJ 0.04507 2.19% 0.04057 0.046 0.043 1.070

CENAM -0.07850 3.39% 0.01695 -0.077 0.067 1.149

LNE 0.00717 1.76% 0.06287 0.009 0.034 0.265

METAS 0.02303 1.96% 0.05075 0.024 0.038 0.632

NMC-

A*STAR 0.01319 1.42% 0.09650 0.015 0.027 0.556

VSL 0.01005 1.41% 0.08744 0.011 0.027 0.407

NMIA -0.03628 1.52% 0.08461 -0.035 0.029 1.207

NIST 0.03089 2.17% 0.04125 0.032 0.043 0.744

VNIIOFI -0.08889 1.39% 0.09696 -0.088 0.026 3.385

MKEH 0.06477 1.58% 0.06883 0.066 0.031 2.129

INM 0.12319 6.55% N.A. 0.125 0.131 0.954

KRISS 0.00000 0.88% 0.21829 0.001 0.016 0.063

Table 8-6. Comparison results for blue LEDs after temperature correction.


MIKES 0.02035 2.13% 0.04765 0.021 0.042 0.500

CMS-ITRI -0.01421 2.52% 0.03388 -0.014 0.050 0.280

PTB -0.00421 1.93% 0.05813 -0.004 0.037 0.108

NMIJ 0.04506 2.27% 0.04203 0.045 0.044 1.023

CENAM -0.07657 3.42% 0.01845 -0.076 0.068 1.118

LNE 0.00749 1.82% 0.06505 0.008 0.035 0.229

METAS 0.02437 2.03% 0.05258 0.025 0.039 0.641

NMC-

A*STAR 0.01324 1.51% 0.09460 0.014 0.029 0.483

VSL 0.01013 1.49% 0.08592 0.010 0.029 0.345

NMIA -0.03558 1.61% 0.08340 -0.035 0.031 1.129

NIST 0.03147 2.23% 0.04348 0.032 0.044 0.727

VNIIOFI -0.08508 1.47% 0.09396 -0.085 0.028 3.036

MKEH 0.06616 1.64% 0.06998 0.067 0.032 2.094

INM 0.12254 6.54% N.A. 0.123 0.131 0.939

KRISS 0.00000 1.01% 0.21088 0.000 0.018 0.000

The DoEs and its uncertainties for blue LEDs are plotted in Fig. 8-3 as dot symbols


the comparison RV.


149

Fig. 8-3. DoE for blue LEDs without and with temperature correction.

8.4. White LEDs

The comparison RV for averaged LED intensity of white LEDs is calculated to be

0.02539, 0.64% ( 2)RV rU k


0.01870, 0.70% ( 2)RV rU k


8-7 and Table 8-8 summarize the comparison results for white LEDs without and with




150

results of CENAM are identified as outliers and not included in the calculation of the RV.

Table 8-7. Comparison results for white LEDs without temperature correction.


MIKES 0.03679 1.80% 0.03376 0.011 0.035 0.314

CMS-ITRI 0.01271 2.13% 0.02432 -0.013 0.042 0.310

PTB 0.02372 1.91% 0.03001 -0.002 0.038 0.053

NMIJ 0.02013 2.18% 0.02304 -0.005 0.043 0.116

CENAM -0.17163 2.91% N.A. -0.197 0.059 3.339

LNE 0.03690 2.13% 0.02415 0.012 0.042 0.286

METAS 0.01646 0.92% 0.13083 -0.009 0.017 0.529

NMC-

A*STAR 0.01072 1.16% 0.08128 -0.015 0.022 0.682

VSL 0.02458 1.79% 0.03418 -0.001 0.035 0.029

NMIA 0.07855 1.01% 0.10666 0.053 0.019 2.789

NIST 0.04653 1.32% 0.06320 0.021 0.025 0.840

VNIIOFI 0.02982 0.83% 0.11148 0.004 0.016 0.250

MKEH 0.03288 1.06% 0.08677 0.007 0.020 0.350

INM 0.12096 5.73% 0.00334 0.096 0.114 0.842

KRISS 0.00000 0.67% 0.24695 -0.025 0.011 2.273

Table 8-8. Comparison results for white LEDs after temperature correction.


MIKES 0.02358 1.91% 0.03484 0.005 0.037 0.135

CMS-ITRI -0.00047 2.18% 0.02657 -0.019 0.043 0.442

PTB 0.02087 1.24% 0.08203 0.002 0.024 0.083

NMIJ 0.01958 1.91% 0.03474 0.001 0.037 0.027

CENAM -0.18187 2.99% N.A. -0.201 0.060 3.350

LNE 0.02847 2.53% 0.01977 0.010 0.050 0.200

METAS 0.00373 1.07% 0.11121 -0.015 0.020 0.750

NMC-

A*STAR 0.01108 1.20% 0.08772 -0.008 0.023 0.348

VSL 0.02307 1.53% 0.05424 0.004 0.030 0.133

NMIA 0.05339 1.09% 0.10640 0.035 0.021 1.667

NIST 0.05157 1.40% 0.06463 0.033 0.027 1.222

VNIIOFI 0.00832 0.90% 0.10696 -0.010 0.017 0.588

MKEH 0.02303 1.13% 0.08459 0.004 0.022 0.182

INM 0.11145 5.62% 0.00402 0.093 0.112 0.830

KRISS 0.00000 0.83% 0.18228 -0.019 0.015 1.267

The DoEs and its uncertainties for white LEDs are plotted in Fig. 8-4 as dot symbols


the comparison RV.


151

Fig. 8-4. DoE for white LEDs without and with temperature correction.

8.5. Diffuser-type Green LEDs

The comparison RV for averaged LED intensity of diffuser-type green LEDs is calculated

to be 0.02219, 0.60% ( 2)RV rU k

for the results without temperature correction,

and 0.02068, 0.64% ( 2)RV rU k

for the results after temperature correction.

Table 8-9 and Table 8-10 summarize the comparison results for diffuser-type green LEDs

without and with temperature correction, respectively. The last column of each table

shows the En criteria of each participant, which is defined as the absolute ratio of Di and


152

U(Di). Note that the results of CENAM and INM are identified as outliers and not

included in the calculation of the RV.

Table 8-9. Comparison results for diffuser-type green LEDs without temperature correction.


MIKES 0.02808 0.91% 0.10905 0.006 0.017 0.353

CMS-ITRI 0.01191 2.23% 0.01819 -0.010 0.044 0.227

PTB 0.01080 1.25% 0.05846 -0.011 0.024 0.458

NMIJ 0.02927 1.48% 0.04120 0.007 0.029 0.241

CENAM -0.12031 3.35% N.A. -0.143 0.067 2.134

LNE 0.05492 1.04% 0.08364 0.033 0.020 1.650

METAS 0.01437 1.25% 0.05819 -0.008 0.024 0.333

NMC-

A*STAR 0.01084 1.17% 0.06663 -0.011 0.023 0.478

VSL 0.02746 1.36% 0.04935 0.005 0.026 0.192

NMIA 0.02472 1.16% 0.06732 0.003 0.022 0.136

NIST 0.05872 1.22% 0.06076 0.037 0.024 1.542

VNIIOFI -0.00231 1.15% 0.05622 -0.025 0.023 1.087

MKEH 0.03739 0.76% 0.11945 0.015 0.014 1.071

INM 0.20781 5.59% N.A. 0.186 0.112 1.661

KRISS 0.00000 0.65% 0.21152 -0.022 0.012 1.833

Table 8-10. Comparison results for diffuser-type green LEDs after temperature correction.


MIKES 0.02318 1.06% 0.09758 0.002 0.020 0.100

CMS-ITRI 0.01012 2.29% 0.02078 -0.011 0.045 0.244

PTB 0.01398 1.06% 0.09758 -0.007 0.020 0.350

NMIJ 0.03155 1.39% 0.05672 0.011 0.027 0.407

CENAM -0.12663 3.43% N.A. -0.147 0.069 2.130

LNE 0.05055 1.17% 0.07937 0.030 0.022 1.364

METAS 0.01099 1.27% 0.06730 -0.010 0.025 0.400

NMC-

A*STAR 0.01312 1.25% 0.07022 -0.008 0.024 0.333

VSL 0.02514 1.40% 0.05580 0.004 0.027 0.148

NMIA 0.01235 1.20% 0.07347 -0.008 0.023 0.348

NIST 0.06197 1.31% 0.06353 0.041 0.025 1.640

VNIIOFI -0.00823 1.28% 0.05560 -0.029 0.025 1.160

MKEH 0.03532 0.92% 0.10164 0.015 0.018 0.833

INM 0.18510 5.69% N.A. 0.164 0.114 1.439

KRISS 0.00000 0.82% 0.16042 -0.021 0.015 1.400

The DoEs and its uncertainties for diffuser-type green LEDs are plotted in Fig. 8-5 as

dot symbols and error bars, respectively. The red lines indicate the expanded relative

uncertainty of the comparison RV.


153

Fig. 8-5. DoE for diffuser-type green LEDs without and with temperature correction.


154

9. Discussion

9.1. Test of Consistency

In order to test the consistency of the comparison results, the Birge ratio RB is calculated

by the equation

2

RV

B 20 adj

1

( )

Ni

i i

RN u

, (9-1)

where N is the number of the participants, without counting the pilot, whose results are

used for the calculation of the RV. For this calculation, the data of the outliers are not

used. Note that the consistency is satisfied, if RB ≤ 1.

Table 9-1 shows the calculated Birge ratios of the comparison S3a without and with

temperature correction. The values of RB range from 1.4 to 2.4, which indicate that the

uncertainties of the participants are underestimated. Table 9-1 also shows that the

temperature correction has the effect of decreasing the Birge ratios and, hence,

improving the consistency. This verifies that the temperature correction based on the

junction voltage measurement described in Chapter 3 is capable to correct the

systematic errors of the artifact LEDs due to different measurement conditions.

Table 9-1. Birge ratio of the comparison S3a.

LED type Birge ratio

without T correction

Birge ratio after T

correction

Red 1.847 1.434

Green 1.714 1.738

Blue 2.409 2.247

White 1.992 1.465

Diffuse green 1.833 1.629

9.2. Accuracy of Alignment

As LEDs have a narrow angular distribution of emission, the mechanical alignment of

LEDs is known as one of the most critical components in practice affecting the

measurement accuracy of averaged LED intensity. In order to check this, the pilot

circulated the specially-designed diffuser-type green LED that shows a spatial angular

distribution being not sensitive to the alignment. Difference between the results for the

normal and diffuser-type green LEDs of each participant can give information if the

measurement of the participant contains any significant error in alignment. Table 9-2

shows the summary of the DoEs for the normal and diffuser-type green LEDs with their


155

differences expressed in per cent.

Table 9-2. DoEs for the normal and diffuser-type green LEDs (after temperature correction).

participant DoE for normal

green LEDs

DoE for

diffuser-type

green LEDs

difference

MIKES 0.002 0.002 0.0%

CMS-ITRI -0.012 -0.011 0.1%

PTB 0.001 -0.007 -0.8%

NMIJ 0.019 0.011 -0.8%

CENAM -0.126 -0.147 -2.1%

LNE 0.030 0.030 0.0%

METAS -0.001 -0.010 -0.9%

NMC-A*STAR -0.002 -0.008 -0.6%

VSL 0.013 0.004 -0.8%

NMIA -0.063 -0.008 5.5%

NIST 0.036 0.041 0.5%

VNIIOFI -0.033 -0.029 0.4%

MKEH 0.026 0.015 -1.2%

INM 0.118 0.164 4.6%

KRISS -0.012 -0.021 -0.9%

9.3. Accuracy of Color Correction

The narrow spectral bandwidth of LEDs is another important source of systematic errors

in the photometric measurement of LEDs. If a photometer is used for LED measurements,

correction of spectral mismatch, often referred to as color correction, is essential to

achieve high accuracy, which requires both relative spectral distribution of the test LED

and relative spectral responsivity of the photometer. The technical reports of the

participants in Chapter 4 inform that every participant of the comparison S3a uses a

photometer and applies color correction. As we have circulated four different colors of

LEDs (R/G/B/W), analysis of the dependence of the comparison results upon the LED

colors can provide important information on the accuracy of color correction. Table 9-3

summarizes the DoEs of each participant for different colors of LEDs, which are based on

the temperature corrected data.

Table 9-3. DoEs for different LED colors (after temperature correction).

participant DoE for red

LEDs

DoE for green

LEDs

DoE for blue

LEDs

DoE for white

LEDs MIKES -0.001 0.002 0.021 0.005

CMS-ITRI -0.022 -0.012 -0.014 -0.019

PTB 0.003 0.001 -0.004 0.002

NMIJ -0.021 0.019 0.045 0.001


156

CENAM -0.343 -0.126 -0.076 -0.201

LNE 0.020 0.030 0.008 0.010

METAS -0.028 -0.001 0.025 -0.015

NMC-A*STAR 0.007 -0.002 0.014 -0.008

VSL 0.006 0.013 0.010 0.004

NMIA 0.101 -0.063 -0.035 0.035

NIST 0.031 0.036 0.032 0.033

VNIIOFI 0.037 -0.033 -0.085 -0.010

MKEH -0.022 0.026 0.067 0.004

INM 0.082 0.118 0.123 0.093

KRISS -0.011 -0.012 0.000 -0.019

Fig. 9-1 shows plots of the data in Table 9-3. We classified the participants to three

groups. The first group shown on the top plot in Fig. 9-1 have only a weak (< 1 %)

dependence of DoE on the LED colors. The second group shown on the middle plot in

Fig. 9-1 have a moderate (2 % ~ 5 %) dependence of DoE on the LED colors. Especially,

the results of many participants have a maximum or a minimum for blue LEDs. The last

group shown on the bottom plot in Fig. 9-1 have a large (> 5 %) dependence of DoE on

the LED colors. The results of Table 9-3 and Fig. 9-1 can be useful for the participants to

investigate the unknown systematic errors in their color correction.


157

Fig. 9-1. Plots of DoEs for different colors of LEDs (R, G, B, W). The participants are classified to three groups.


158

10. Summary

The measurement of averaged LED intensity in the CIE-B condition is compared by

circulating five different types of artifact LEDs (red, green, blue, white, and diffuser-type

green) to 15 NMIs (including the pilot). The artifact LEDs are prepared by the functional

seasoning to enable a temperature correction based on the junction voltage

measurement. The comparison reference values and the unilateral degrees of equivalence

(DoEs) of each participant are calculated for each type of LEDs from the reported

measurement results. Table 10-1 shows the summary of the DoEs and their uncertainties

of each participant for each type of LEDs as the comparison result.

Table 10-1. Summary of the unilateral DoEs and their uncertainties for APMP.PR-S3a (temperature correction applied).

NMI

RED GREEN BLUE WHITE DIFFUSE

DoE U of

DoE DoE

U of

DoE DoE

U of

DoE DoE

U of

DoE DoE

U of

DoE

MIKES -0.001 0.039 0.002 0.040 0.021 0.042 0.005 0.037 0.002 0.020

CMS-ITRI -0.022 0.049 -0.012 0.044 -0.014 0.050 -0.019 0.043 -0.011 0.045

PTB 0.003 0.034 0.001 0.026 -0.004 0.037 0.002 0.024 -0.007 0.020

NMIJ -0.021 0.032 0.019 0.035 0.045 0.044 0.001 0.037 0.011 0.027

CENAM -0.343 0.062 -0.126 0.072 -0.076 0.068 -0.201 0.060 -0.147 0.069

LNE 0.020 0.032 0.030 0.027 0.008 0.035 0.010 0.050 0.030 0.022

METAS -0.028 0.028 -0.001 0.026 0.025 0.039 -0.015 0.020 -0.010 0.025

NMC-

A*STAR 0.007 0.029 -0.002 0.027 0.014 0.029 -0.008 0.023 -0.008 0.024

VSL 0.006 0.026 0.013 0.028 0.010 0.029 0.004 0.030 0.004 0.027

NMIA 0.101 0.043 -0.063 0.030 -0.035 0.031 0.035 0.021 -0.008 0.023

NIST 0.031 0.034 0.036 0.032 0.032 0.044 0.033 0.027 0.041 0.025

VNIIOFI 0.037 0.021 -0.033 0.034 -0.085 0.028 -0.010 0.017 -0.029 0.025

MKEH -0.022 0.024 0.026 0.024 0.067 0.032 0.004 0.022 0.015 0.018

INM 0.082 0.116 0.118 0.114 0.123 0.131 0.093 0.112 0.164 0.114

KRISS -0.011 0.018 -0.012 0.017 0.000 0.018 -0.019 0.015 -0.021 0.015


159

Acknowledgement

The pilot work of this comparison is partly supported by the Korean Ministry of

Knowledge and Economy under the project of LED standardization, grant B0010209.


160

Appendix A: Technical Protocol

The pdf-file can be opened by a double-click on the image below.


161

Appendix B: Review of Relative Data



162

Appendix C: Comments from Review of Relative Data



163

Appendix D: Comments from Review of Uncertainty Budgets



164

Appendix E: Identification of Outliers



165

Appendix F: Comments and Revision to Draft A Report

Comments from PTB to Data Analysis

Results on 11 April 2011

Replies by the pilot on 17 June 2011

Enclosed please find copies of your files

with some marked blue cells. We think

there are some small bugs.

I have checked them and corrected. Thank

you!

It is possible to refer this comparison to

KCRV using link laboratories.

In principle yes. But the related KC, e.g. of

luminous flux, was done with a different

artifact so that it cannot be directly

compared to this LED comparison. That is

also the reason why this is a

supplementary comparison. We can try to

do such a linkage as an interesting study,

but not as a part of the comparison report.

The resulting excel graphic looks a little bit

strange. We feel is should look similar like

the following graphic (uDoE should be

plotted around DoE):

I agree and I checked that this is also

common for KCs. I will modify the graphs

as you suggest.

It may be helpful to calculate the Birge

ratio to get information about the

consistency of the comparisons. It is

calculated from the internal and external

This is a good suggestion. I will surely try

to calculate both the Birge ratio and the En

values and include the results in the final

report. This will provide valuable


166

consistency. A value of close to 1 or less

indicates that the results are consistent.

Values greater than 1 are not.

in

extB

u

uR with

n

i

i

n

i

ii

Dun

DuD

u

1

2

1

2

ext

)()1(

)](/[

and

2/1

1

2

in )(

n

i

iDuu .

For luminous flux we found values around

2 for most cases. For luminous intensity

(without diffuse LEDs) we found values

around 1. Please see enclosed jpg files (I

apologize this jpg, but is takes a while to

get nice prints with mathematica). We also

calculated the criteria by

)(2Absin,

i

i

DoEu

DoEE

Values greater than 1 indicate a too small

uncertainty of the participant. So we

suggest to use specific enlargements of the

participant uncertainties in that way that

the Birge ratio is equal or less 1 and

criteria is close to 1. This procedure also

would solve the problem of outliers.

information to the next version of the KC

guidelines which should include a

procedure of consistency check and of a

better outlier selection.

Comments from PTB to Draft A Report

on 19 Oct 2011

Replies by the pilot on 22 Nov 2011

We found some typing errors in the draft

A paper. Enclosed please find our errata

ZIP-file.

I have checked the errors. But all the errors

you found were the corrections of the

uncertainty budgets of PTB. These,

however, cannot be corrected in the draft

A report stage, because they are already


167

reviewed by the participants. This is

communicated via email on 21.10.2011.

PTB has acknowledged this and confirms

that these corrections do not affect the

comparison results. Therefore, the

corrections are not considered in the

revision of the draft A report.

The Plots Fig. 9-1 of S3a and S3b are very

helpful. It would be great to have these

plots for S3c, too.

In case of S3c, the plots such as Fig. 9-1 of

S3a and S3b were not easy because a 2

dimensional plot is required to make

systematic effects visible. I will try to realize

this in the next revision of the S3c report,

but I should also manage the workload.

Based on the results data, however, each

participant can make such analysis to

investigate the systematic effect of his

results.

The appendices should include all

important comments, suggestions and

recommendations of the participants to

simplify future comparisons. For example

our Suggestions PTB.docx of 15.04.2011.

I will make another appendix to record the

comments during the draft A report

procedure.

The tables in chapter 8 should include the

criteria

)(2Absin,

i

i

DoEu

DoEE

that would be helpful to evaluate the

stated uncertainty by each participants.

I will consider this in the revision.

The Birge ratios stated in table 9-1

especially for S3a and S3a are often

significant greater than 1. I think the

I agree that the large Birge ratio means

that the uncertainties of the participants

are underestimated. I wrote this also in the


168

meaning of that is, that some stated

uncertainties are too small. Please, refer

the related En criteria.

Here we have an additional hint for that.

The first diagram from S3a (intensity)

shows a relative flat DoE around 0% of PTB

results. But the second diagram from S3b

(flux) shows relative big differences

between (R,G) and (B,W) LEDs. The

luminous flux values were determined by a

goniophotometer directly after the

luminous intensity measurement with the

same operation state of the LED and in the

same system without new alignment of the

LED. So there is no reason for that

difference. We know from hundreds of

measurements that the integration

capability of the goniophotometer has a

very high reproducibility.

So I think this a hint for an inconsistency

of the data as we know from the Birge

ratios.

report. Your statement will be documented

in the Appendix of the revised report.


169

List of Revisions from A-1 to A-2

Draft A-1 Draft A-2

Page 121, section 5.4, the first line: “June ~

July 2008 (the exact dates not reported)”

Corrected to “from 16 June to 2 July 2008”

based on the result verification records.

Chapter 8, the first paragraph of each

section.

Addition of a sentence “The last column of

each table Table 8-2shows the En criteria of

each participant, which is defined as the

absolute ratio of Di and U(Di).”

Chapter 8, Table 8-1 ~ Table 8-10. Addition of a new column with the

calculated En criteria values.

After Chapter 10 Addition of <Acknowledgment> by the

pilot.

After Appendix E Addition of <Appendix F: Comments and

Revision to Draft A Report>

APMP supplementary comparison 1

Technical Protocol on


LED Measurements




Approved in January 2008, Revised in November 2008 due to change of participants list

Contents

1. INTRODUCTION........................................................................................................................................ 2

2. ORGANIZATION........................................................................................................................................ 2

2.1. CONDITION OF PARTICIPATION ............................................................................................................... 2 2.2. LIST OF PARTICIPANTS............................................................................................................................ 3 2.3. FORM OF COMPARISON ........................................................................................................................... 4 2.4. TIMETABLE............................................................................................................................................. 4 2.5. TRANSPORT AND HANDLING OF ARTEFACTS ........................................................................................... 6

3. DESCRIPTION OF ARTEFACTS ............................................................................................................ 7

4. MEASUREMENT INSTRUCTIONS ........................................................................................................ 9

4.1. AVERAGED LED INTENSITY (S3A) ......................................................................................................... 9 4.2. TOTAL LUMINOUS FLUX (S3B).............................................................................................................. 11 4.3. EMITTED COLOUR (S3C) ....................................................................................................................... 12

5. REPORTING OF RESULTS AND UNCERTAINTIES ........................................................................ 12

5.1. AVERAGED LED INTENSITY (S3A) ....................................................................................................... 12 5.2. TOTAL LUMINOUS FLUX (S3B).............................................................................................................. 13 5.3. EMITTED COLOUR (S3C) ....................................................................................................................... 13

6. PREPARATION OF COMPARISON REPORT.................................................................................... 14

APPENDIX 1: INSPECTION REPORT ON RECEIPT OF ARTEFACTS................................................. 15

APPENDIX 2: RESULT REPORT OF AVERAGED LED INTENSITY (S3A).......................................... 16

APPENDIX 3: RESULT REPORT OF TOTAL LUMINOUS FLUX (S3B) ................................................ 17

APPENDIX 4: RESULT REPORT OF EMITTED COLOUR (S3C) ........................................................... 18

Technical protocol on comparison of LED measurements



1. INTRODUCTION

Under the Mutual Recognition Arrangement (MRA), the metrological equivalence of national measurement standards will be determined by a set of key comparisons chosen and organized by the consultative committees of CIPM working closely with regional metrology organizations (RMOs). In addition, RMOs can organize supplementary comparisons which should be carried out in the same procedure as that of key comparisons following the guidelines established by BIPM1.

At its meeting in December 2006, Asia Pacific Metrology Programme (APMP) Technical Committee of Photometry and Radiometry (TCPR) proposed several regional comparisons in the field of optical radiation metrology. One of those, a set of photometric quantities of light-emitting diodes (LEDs) has been agreed to be conducted with Korea Research Institute of Standards and Science (KRISS) of Republic Korea as the pilot institute. It is also decided that APMP TCPR invites the institutes of other RMOs to participate this supplementary comparison.

In March 2007, the first invitation to participate is distributed to the members of Consultative Committee of Photometry and Radiometry (CCPR) of CIPM by the chairperson of APMP TCPR. Based on the responses to this invitation, a provisional list of participants is prepared.

Three measurement quantities of LEDs are selected for the comparison, which are listed as service categories for Calibration and Measurement Capabilities (CMCs): averaged LED intensity defined by International Commission on Illumination (CIE), total luminous flux of LEDs, and emitted colour of LEDs expressed as chromaticity coordinates (x, y) according to the CIE 1931 standard colorimetric system.2

It should be noted that total luminous flux is the measurement quantity for CCPR-K4. The current supplementary comparison of total luminous flux of LEDs is, however, not to be linked to this KC, but can be regarded as a pilot study testing the suitability of LEDs as an alternative artefact for CCPR-K4.

This document is to treat the technical protocol for the comparison of LED measurements, and has been prepared by KRISS and agreed by all the participants on the preliminary list.

2. ORGANIZATION

2.1. CONDITION OF PARTICIPATION

KRISS is acting as the pilot institute in the comparison among the participants.

Three comparisons for three measurement quantities are conducted simultaneously by circulating one artefact set. The participant can decide to take part in only one or two of the three comparisons by selecting the measurement quantities. However, it should be declared with the confirmation of participation and stated in the technical protocol.

All the participants must be able to demonstrate traceability to an independent realization of each quantity, or make clear the route of traceability via another named laboratory.

By their declared intention to participate in this comparison, the laboratories accept the general instructions and the technical procedures written down in this document and commit themselves to follow the procedures strictly.

1 Guidelines for CIPM Key Comparisons, March 1999 (modified in October 2003). Available at http://www.bipm.fr/en/convention/mra/guidelines_kcs/ 2 Measurement of LEDs, CIE Technical Report 127-1997.

http://www.bipm.fr/en/convention/mra/guidelines_kcs/



Once the protocol has been agreed, no change to the protocol may be made without prior agreement of all the participants.

2.2. LIST OF PARTICIPANTS

(Nr.) NMI

country contact person email address post address participating comparisons

(1) KRISS

Rep. Korea Seongchong

Park, Dong-Hoon Lee

[email protected] [email protected]

Division of Physical Metrology Korea Research Institute of Standards

and Science 1 Doryong-Dong, Yuseong-Gu Daejeon 305-340, Rep. Korea

all (S3a, S3b,

S3c)

(2)3 NMC-

A*STAR Singapore

Yuanjie Liu, Gan Xu

[email protected]

[email protected]

Optical Metrology Department National Metrology Centre

1 Science Park Drive Singapore 118221

all

(3) MIKES

Finland Pasi Manninen [email protected]

Metrology Research Institute Helsinki University of Technology

P.O.Box 3000 FI-02015 TKK, Finland

all

(4) NIST

USA Cameron Miller,

Yoshi Ohno Yuqin Zong

[email protected]@nist.gov

[email protected]

Optical Technology Division National Institute of Science and

Technology 100 Bureau Drive, Mailstop 8442

Gaithersburg, MD 20899-8442, USA

all

(5) CMS-ITRI

Chinese Taipei

Cheng-Hsien Chen

[email protected]

CMS/ITRI Rm. 301, Bldg. 16, 321, Sec. 2,

Kuang Fu Rd. Hsinchu, Taiwan 300, R.O.C.

all

(6) PTB

Germany Matthias

Lindemann Robert Maass

[email protected]

[email protected]

Physikalisch-Technische Bundesanstalt

AG 4.15, Goniophotometrie Bundesallee 100,

D-38116 Braunschweig, Germany

all

(7) CENAM

Mexico

Laura P. González, Anayansi Estrada,

Eric Rosas

[email protected]@[email protected]

División de Óptica y Radiometría Centro Nacional de Metrología

km 4,5 Carretera a Los Cués 76241, El Marqués, Querétaro,

México

all

(8)

NMIJ Japan

Kenji Godo, Terubumi Saito

[email protected] [email protected]

Optical Radiation Section Photometry and Radiometry Division

National Institute of Advanced Industrial Science and Technology 1-1-1, Umezono, Tsukuba, Ibaraki,

JAPAN 305-8563

all

(9) METAS

Switzerland Peter Blattner Peter.Blattner@metas

.ch

Federal Office of Metrology Lindenweg 50, 3003 Bern-Wabern

Switzerland all

(10) NPL

UK Paul Miller, Nigel Fox

[email protected]

[email protected]

National Physical Laboratory Hampton Road, Teddington, Middx,

TW11 0LW, UK all

(11) LNE

France Jimmy Dubard [email protected]

Laboratoire National de Métrologie et d’Essais

29, avenue Roger Hennequin 78197 TRAPPES, FRANCE

all

3 Formerly SPRING


(12) NMi VSL

The Netherlands

Eric W.M. van der Ham, M.Charl

Moolman

[email protected]@NMi.nl

NMi Van Swinden Laboratorium B.V. Department Electricity, Radiation and

Length Section Optics Thijsseweg 11, 2629 JA Delft

Zuid-Holland, The Netherlands

all

(13) NMIA

Australia Philip Lukins Philip.Lukins@measu

rement.gov.au

National Measurement Institute of Australia

2 Bradfield Rd Lindfield, NSW 2070, Australia

all

(14) VNIIOFI

Russia Tatiana

Gorshkova [email protected]

All-Russian Research Institute for Optical and Physical Measurements

Ozernaya 46 119361 Moscow, Russia

all

(15) MKEH

Hungary George Andor [email protected]

Magyar Kereskedelmi és Engedélyezési Hivatal (MKEH)

Németvölgyi út 37-39 H-1124 Budapest XII.

Hungary

all

(16) INM

Romania Mihai

Simionescu mihai.simionescu@in

m.ro

Institutul National de Metrologie Sos. Vitan Barzesti nr.11, Sector 4

Bucharest, Romania all

2.3. FORM OF COMPARISON

The comparison is carried out by distributing 8 sets of the artefact standard LEDs prepared and provided by the pilot. Each set of the artefact LEDs contains 14 pieces of LED, consisting of 12 lamp-type, 5-mm diameter LEDs (3 x Red, 3 x Green, 3 x Blue, 3 x White) and 2 specially-designed diffuser-type green LEDs. The specifications, preparation, and characteristics of the standard LEDs are described in Chapter 3.

The comparison runs as a star-type. The pilot sends to each participant one set of the artefact LEDs after preparation and characterisation. The participant measures (1) the averaged LED intensity in the CIE condition B, and/or (2) the total luminous flux, and/or (3) the chromaticity coordinate CIE1931 (x,y) of every artefact LEDs according to the introductions described in Chapter 4. After the measurement, the participant sends the artefact set back to the pilot, who characterises it again to check out a possible drift or change. The measurement results should be reported to the pilot as soon as possible after the measurement is finished according to the guidelines in Chapter 5.

The timetable given below shows an overview on how the comparison is to be preceded. Since the preparation of the artefact LEDs takes much time (over 300 hours) due to seasoning process, the pilot requires at least one month preparing the artefact LEDs ready for delivery. The pilot tries to provide as many artefact sets as possible so that the circulation runs without significant loss of time (multiple star-type circulation).

Each participant has two months for measurement after the receipt of the artefact set. With its confirmation to participate, each participant has confirmed that it is capable of performing the measurements in the time allocated to it. If anything happens so that it can not meet the timetable, the participant must contact the pilot immediately.

2.4. TIMETABLE

Time Activity of pilot Activity of participants

July 2007 ~ January 2008

- Preparation of artefact sets (#1 ~ #8) - Preparation of technical protocol draft

- Review of technical protocol draft



January 2008 - Finalization and approval of technical protocol by APMP TCPR

February 2008

- Control measurement of artefact set #1 and #2

- Delivery of artefact set #1 to MIKES - Delivery of artefact set #2 to CMS-ITRI

March 2008


- Delivery of artefact set #3 to PTB - Delivery of artefact set #4 to NMIJ

- Receipt of artefact set #1 in MIKES, Finland

- Receipt of artefact set #2 in CMS-ITRI, Taiwan

April 2008


- Delivery of artefact set #5 to CENAM- Delivery of artefact set #6 to LNE

- Receipt of artefact set #3 in PTB, Germany

- Receipt of artefact set #4 in NMIJ, Japan

May 2008


- Delivery of artefact set #7 to METAS - Delivery of artefact set #8 to NMC-A*STAR

- Receipt of artefact set #5 in CENAM, Mexico

- Receipt of artefact set #6 in LNE, France

- Return of artefact set #1 and #2 to KRISS (MIKES, CMS-ITRI)

June 2008


- Delivery of artefact set #1 to NMi-VSL

- Delivery of artefact set #2 to NMIA

- Receipt of artefact set #7 in METAS, Switzerland

- Receipt of artefact set #8 in NMC-A*STAR, Singapore

- Return of artefact set #3 and #4 to KRISS (PTB, NMIJ)

July 2008


- Delivery of artefact set #3 to NIST - Delivery of artefact set #4 to NPL

- Receipt of artefact set #1 in NMi-VSL, The Netherlands

- Receipt of artefact set #2 in NMIA, Australia

- Return of artefact set #5 and #6 to KRISS (CENAM, LNE)

August 2008


- Delivery of artefact set #5 to VNIIOFI- Delivery of artefact set #6 to MKEH

- Receipt of artefact set #3 in NIST, USA

- Receipt of artefact set #4 in NPL, UK

- Return of artefact set #7 and #8 to KRISS (METAS, NMC-A*STAR)

September 2008 - Control measurement of artefact set #7 and #8

- Receipt of artefact set #5 in VNIIOFI, Russia

- Receipt of artefact set #6 in MKEH, Hungary

- Return of artefact set #1 and #2 to KRISS (NMi-VSL, NMIA)

October 2008 - Control measurement of artefact set #1 and #2

- Delivery of artefact set #7 to INM

- Return of artefact set #3 and #4 to KRISS (NIST, NPL)



November 2008 - Control measurement of artefact set #3 and #4

- Return of artefact set #5 and #6 to KRISS (VNIIOFI, MKEH)

- Receipt of artefact set #7 in INM, Romania

December 2008


- Control measurement of artefact set #7

- Return of artefact set #7 to KRISS (INM)

January 2009 ~ April 2009

- Pre-Draft A process 1: distribution of uncertainty budget - Pre-Draft A process 2: review of relative data

May 2009 ~ June 2009

- Draft A report: preparation and distribution

July 2009 ~ August 2009

- Draft A report: review and approval by the participants

Sept. 2009 ~ October 2009

- Draft B report: preparation and submission to TCPR (Or Draft A-2 report process, if required)

2.5. TRANSPORT AND HANDLING OF ARTEFACTS

Each set of 14 artefact LEDs is transported in a wooden box (size 90 cm x 90 cm x 80 cm) with conductive foam matting, where the LEDs are pinned down at the specified positions. Packaging of the box should be sufficiently robust to be sent by courier, but precautions must be taken to prevent any damage by mechanical impact, heat, water, and moisture. The artefact set will be accompanied by a suitable customs carnet (where appropriate) or documentation identifying the items uniquely.

Each participating laboratory covers the cost for its own measurements, transportation and any customs charges as well as for any damages that may have occurred within its country.

The artefact LEDs should be visually inspected immediately upon receipt. However, care should be taken to ensure that the LEDs have sufficient time to acclimatise to the laboratory environment thus preventing any condensation, etc. The condition of the artefact LEDs and associated packaging should be noted and communicated via email and fax to the pilot by using the form APPENDIX 1: INSPECTION REPORT ON RECEIPT OF ARTEFACTS.

The artefact LEDs should be handled only by the authorized persons, who are well aware of the cautions stated in the manufacturer’s specification sheets of the artefact LEDs.

LEDs can be damaged by static electricity or surge voltage. Using an anti-static wrist band is strongly recommended. When the LEDs are not installed for measurement, they should always be kept at the specified positions on the conductive foam matting in the package box, which prevents not only electrostatic and mechanical damages but also confusion in identifying each LED.

The LEDs should never be touched with bare hands. Please use an anti-static vinyl glove in handling the LEDs. No cleaning of LEDs should be attempted except using dry air.

The mechanical condition of the LEDs should never be changed by actions such as soldering, cutting, polishing, and bonding.

If an artefact LED is damaged or shows any unusual property during operation, the operation should immediately be terminated and the pilot should be contacted.

After measurement, the artefact LEDs should be repackaged as received. Ensure that the content of the package is complete before shipment.




3. DESCRIPTION OF ARTEFACTS

The artefact LEDs are prepared from the commercially available “raw” LEDs in the following procedure:

1. Seasoning: the raw LEDs are pre-burned for more than 300 hours while the temporal change of their electrical and optical properties are recorded. The temporal drift and the temperature dependence of the optical characteristics of each LED are determined during the seasoning process.

2. Selection: based on the seasoning characteristics, the LEDs with predictable seasoning characteristics are selected as the artefact LEDs for the comparison.

3. Test measurement: the photometric quantities of the artefact LEDs are measured by the pilot before sent to each participant. The measurement by the pilot is repeated when the artefacts are received back from the participant after the measurement. If the measured drift of an artefact is greater than expected from the seasoning, it should be replaced by another seasoned LED of the same type for the next measurement round.

The “raw” LEDs used in this comparison are manufactured by Nichia Corporation.4 The selected models are listed in the following table with the specifications provided by the manufacturer (pdf-files included).

colour model initial characteristics in specifications

(forward current 20 mA, 25 ºC) specification sheets (file)

RED NSPR518S

forward voltage 2.2 V luminous intensity 1 cd dominant wavelength 625 nm spectral bandwidth 15 nm (FWHM) angular directivity 50º (FWHM)

Adobe Acrobat 7.0 Document

GREEN NSPG518S

forward voltage 3.5 V luminous intensity 2 cd dominant wavelength 525 nm spectral bandwidth 40 nm (FWHM) angular directivity 40º (FWHM)


BLUE NSPB518S

forward voltage 3.6 V luminous intensity 0.6 cd dominant wavelength 470 nm spectral bandwidth 30 nm (FWHM) angular directivity 40º (FWHM)


WHITE NSPW515BS

forward voltage 3.6 V luminous intensity 0.7 cd chromaticity near x = 0.31, y = 0.32 angular directivity 70º (FWHM)


The mechanical dimensions are the same for every raw LED as summarized below. The detailed drawing of the LEDs can be found in the specification sheets.

- lamp diameter: 5 mm (diffusion type, epoxy resin mold)

- lamp base diameter: 5.6 mm (LED’s outer diameter)

- lamp length (length of the lamp part with diameter ≤ 5 mm): 7.3 mm

4 More information on the LEDs available at http://www.nichia.co.jp/

http://www.nichia.co.jp/



- wire length (measured from backside of lamp): 20.3 mm for cathode, 22.3 mm for anode

- wire thickness: 0.5 mm

- wire distance: 2.5 mm

In the seasoning process, the relative luminous intensity and spectral distribution of each LED is recorded together with its junction temperature as a function of time for burning time of longer than 300 hours, while the ambient temperature is periodically varied from 18 ºC to 33 ºC. From the recorded data, the temperature dependence and the slow-varying drift characteristics of the LED’s photometric and colorimetric quantities can be separately determined.5 The pilot keeps and uses the measured data and characteristics of each artefact LED during the seasoning, first, to monitor and compensate the temperature effect of the measurands and, second, to control if the drift of the artefact LEDs occurred during the comparison is within the expected range. Note that the record of the junction voltage with the comparison measurands for each artefact LED is essential for this purpose.

Since the mechanical alignment of a LED is known as one of the most critical components affecting the measurement accuracy of averaged LED intensity, the pilot circulates, in addition to the 12 standard-type artefact LEDs, two samples of a specially-designed diffuser-type LED that shows a spatial emission distribution being not sensitive to the alignment. This diffuser-type artefact LED is constructed by putting a green LED (NSPG518S) into a cylinder-type cap with an opal diffuser, as shown in Fig. 1, and should provide a possibility to analyze the result of the comparison. Note, however, that this diffuser-type artefact LEDs are not used in the measurement of total luminous flux.

Fig. 1 Schematic drawing of a diffuser-type artefact LED.

One artefact set finally contains 14 artefact LEDs, and the pilot prepares and circulates 8 different sets for the 14 participants. Each participant receives and measures one among these artefact sets according to the timetable in Section 2.4. Each artefact set is identified with a serial number (set #1, set #2, etc.) and the 14 LEDs in one set is identified and positioned in a package box as shown in Fig. 2. Note that one artefact LED is uniquely identified in a form #N-X-M with three codes: (1) #N as artefact set number (N = 1, 2, …, 8), (2) X as LED colour and type code (X = R for red, G for green, B for blue, W for white, D for diffuser-type), and (3) M as sample serial number for each type (M = 1, 2, 3). As the individual LED could not be indicated by writing the full identification code on the LED due to the small size, only the sample number M of each LED is marked on the wires according to the colour code as shown in the right-hand part of Fig. 2.

5 Seongchong Park et al., Metrologia 43, 299 (2006); Proc. SPIE 6355, 63550G-1 (2006)

13.5 mm

8.3 mm

diffuser diameter 8.3 mm

[side view] [front view]



Fig. 2 Identification of individual LEDs in the box of one artefact set.

4. MEASUREMENT INSTRUCTIONS

4.1. AVERAGED LED INTENSITY (S3A)

The averaged LED intensity (unit: cd) of each artefact LED is to be measured in the standard condition B defined by CIE, as depicted in Fig. 3. 6 Either an illuminance meter or a spectroradiometer is used as the detector measuring the illuminance Ev for a circular area with size A = 100 mm2 at a distance d = 100 mm from the front tip of the LED. This is also valid for the diffuser-type LEDs with a flat front tip (see Fig. 1).

Fig. 3 Measurement condition for averaged LED intensity (CIE standard condition B).

The LED should be mounted so that the geometric axis of the LED is aligned to coincide with the normal of the reference plane of the detector head at the centre of the aperture area. The geometric axis of a LED is defined as the axis of rotational symmetry of the LED lamp cap,

6 Measurement of LEDs, CIE Technical Report 127-1997.

R-1 R-2 R-3

G-1 G-2 G-3

B-1 B-2 B-3

D-1 D-2

[wire marking]

- black for X-1

- red for X-2

- blue for X-3

(X = R/G/B/W/D)

W-1 W-2 W-3

Detector head

distance d

d = 100 mm ( = 0.01 sr)

circular aperture with size A =100 mm2


which, in general, does not coincide with the optical axis of the light emission, as depicted in Fig. 4. Each participant may use a different method to achieve the target alignment condition with high reproducibility. For instance, one can confirm the target alignment condition by visually inspect the LED from the detector head position to check the rotational symmetry of the cap, as shown in Fig. 5.

optical axis


Fig. 4 Definition of the geometric axis of a LED used for alignment to measure its averaged LED intensity.

Fig. 5 Inspection of alignment for the averaged LED intensity measurement by viewing the LED from the detector head position using a camera.

The LED should be mounted so that the backward emission, i.e. radiation emitted from the LED back surface to the direction of the connection wires, does not contribute to the detector signal. For this purpose, it is recommended to design the LED holder so that the backward emission is effectively scattered out of the measurement axis and blocked by a baffle.

The measurement should be performed by applying a constant forward current of 20 mA at an ambient temperature as close as 25 ºC for every artefact LED. In order to determine the junction temperature of the LED, the junction voltage between the anode and cathode should be measured in a 4-wire connection and recorded simultaneously with the value of averaged LED intensity, as shown in Fig. 6.

geometric axis LED front tip

[side view] [front view]

LED lamp cap

well-aligned slightly tilted


anode

cathode

current source

+

−

+

voltmeter

I = 20 mA

−

Fig. 6 Circuit diagram of the 4-wire connection used to measure the junction voltage of a LED while applying the forward current.

The measurement of averaged LED intensity and junction voltage should be performed after a warming-up time of longer than 5 minutes. The turn-on time and turn-off time of each measurement sequence should be recorded so that the total burning time of each artefact LED can be determined and reported.

The measurement should be repeated and reproduced so that its uncertainty can be evaluated with sufficient confidence.

4.2. TOTAL LUMINOUS FLUX (S3B)

The luminous flux integrated for the whole 4 direction (unit: lm) of each artefact LED is to be measured using either a goniophotometer or an integrating sphere. Note, however, that the two diffuser-type LEDs are excluded for the measurement of total luminous flux.

The LED should be mounted so that the contribution of the backward emission is properly included in the total luminous flux. For this purpose, it is recommended to mount the LED back surface as far as possible from the holder and to minimize the near-field absorption in the holder.

The measurement should be performed by applying a constant forward current of 20 mA at an ambient temperature as close as 25 ºC for every artefact LED. In order to determine the junction temperature of the LED, the junction voltage between the anode and cathode should be measured in a 4-wire connection and recorded simultaneously with the value of total luminous flux, as shown in Fig. 6.

The measurement of total luminous flux and junction voltage should be performed after a warming-up time of more than 5 minutes. The turn-on time and turn-off time of each measurement sequence should be recorded so that the total burning time of each artefact LED can be determined and reported.





4.3. EMITTED COLOUR (S3C)

The chromaticity coordinate CIE1931 (x,y) of the emitted colour of each artefact LED is to be determined by measuring the spectral distribution in the geometric condition of averaged LED intensity as shown in Fig. 3.7

The measurement should be performed by applying a constant forward current of 20 mA at an ambient temperature as close as 25 ºC for every artefact LED. In order to determine the junction temperature of the LED, the junction voltage between the anode and cathode should be measured in a 4-wire connection and recorded simultaneously with chromaticity coordinate, as shown in Fig. 6.

The measurement of chromaticity coordinate and junction voltage should be performed after a warming-up time of more than 5 minutes. The turn-on time and turn-off time of each measurement sequence should be recorded so that the total burning time of each artefact LED can be determined and reported.


5. REPORTING OF RESULTS AND UNCERTAINTIES

5.1. AVERAGED LED INTENSITY (S3A)

The measurement results should be reported to the pilot via email and fax by using the form APPENDIX 2: RESULT REPORT OF AVERAGED LED INTENSITY (S3A) immediately after the measurement is finished.

In addition to the result report, the participant is requested to provide the pilot a technical report containing the information listed in the following. This free-form report should be sent to the pilot via email as a Microsoft Word file within one month after the completion of measurement.

- Measurement setup and instruments used

- Mounting and alignment method, including a picture of the LED holder

- Traceability of measurement

- Detailed uncertainty budget for averaged LED intensity including values, evaluation type, probability distribution, degree of freedom, and sensitivity coefficient of each uncertainty component

- Detailed uncertainty budget for junction voltage including values, evaluation type, probability distribution, degree of freedom, and sensitivity coefficient of each uncertainty component

In the uncertainty budgets of the technical report, the participant should state whether and how an uncertainty component is artefact-dependent.

The pilot requests the participants to explicitly include the following uncertainty components in the uncertainty budgets to analyze the critical contributions:

- Component due to axis alignment. Note that the sensitivity to both angular (tilting) and translational (centring) misalignment should be separately considered.

7 This corresponds to a solid angle of 0.01 sr with a detector aperture size of 100 mm2. In case, however, that the aperture size of the instrument cannot be 100 mm2, the emitted colour should be measured for a solid angle of 0.01 sr at an appropriate distance, and the uncertainty budget should include components due to the different geometric condition.



- Component due to current feeding accuracy.

- Component due to stray light in the optical bench. Note that the backward emission of the LED scattered from the LED holder/mount can also contribute to the stray light.

- Component due to spectral mismatch correction, when a filter-type illuminance meter is used. Note that the spectral quantities used for spectral mismatch correction can be strongly correlated.

- For junction voltage: component due to position of junction.8

5.2. TOTAL LUMINOUS FLUX (S3B)

The measurement results should be reported to the pilot via email and fax by using the form APPENDIX 3: RESULT REPORT OF TOTAL LUMINOUS FLUX (S3B) immediately after the measurement is finished.



- Mounting and alignment method, including a picture of the LED holder


- Detailed uncertainty budget for total luminous flux including values, evaluation type, probability distribution, degree of freedom, and sensitivity coefficient of each uncertainty component



The pilot requests the participants to explicitly include the following uncertainty components in the uncertainty budget to analyze the critical contributions:

- Component due to near-field absorption of backward emission


- Component due to stray light, when a goniophotometer is used.

- Component due to spectral mismatch correction, when a filter-type illuminance meter is used. Note that the spectral quantities used for spectral mismatch correction can be strongly correlated.

- Component due to spatial correction, when an integrating sphere is used.

- For junction voltage: component due to position of junction.

5.3. EMITTED COLOUR (S3C)

The measurement results should be reported to the pilot via email and fax by using the form APPENDIX 4: RESULT REPORT OF EMITTED COLOUR (S3C) immediately after the measurement is finished.

8 That means an uncertainty component due to the different distance from the LED junction to the voltage measurement point.






- Detailed uncertainty budget for chromacitycoordinates including values, evaluation type, probability distribution, degree of freedom, and sensitivity coefficient of each uncertainty component



The pilot requests the participants to explicitly include the following uncertainty components in the uncertainty budget to analyze the critical contributions:

- Component due to axis alignment. Note that the sensitivity to both angular (tilting) and translational (centring) misalignment should be separately considered.


- Component in calculating the chromaticity coordinate from the measured spectral distribution. Note that the spectral quantities used for calculation can be strongly correlated.

- For junction voltage: component due to position of junction.

6. PREPARATION OF COMPARISON REPORT

After the measurement schedule of every participant is completed, the pilot prepares the report of the comparisons according to the guidelines by CCPR.9

Since three comparisons are performed together by using one artefact LED set, three reports are to be separately prepared.

Before starting the Pre-Draft A process, the pilot will re-confirm its reception of the artefact sets, the measurement results, and the technical reports from every participant. If any result or report is missing until this time, the pilot will announce a deadline for re-submission. After this deadline, the pilot proceeds the report preparation only with the data submitted so far.

9 Guidelines for CCPR Comparison Report Preparation, Rev. 1 of March 2006. Available at http://www.bipm.org/utils/en/pdf/ccpr_guidelines.pdf

http://www.bipm.org/utils/en/pdf/ccpr_guidelines.pdf



APPENDIX 1: INSPECTION REPORT ON RECEIPT OF ARTEFACTS

Has the artefact set package been opened during transit? (e.g. by Customs) …… Y / N

If Yes, please give details.

Is there any damage to the package box? …… Y / N

If Yes, please give details.

Are the 14 artefact LEDs inside the package box complete and properly fixed into the conductive

matting? …… Y / N

If No, please give details.

Are there any visible signs of damage to the artefact LEDs? …… Y / N

If Yes, please give details (e.g. scratches or contaminations on the lamp, bending of wires, etc).

Is the LED identification sheet prepared by the pilot found in the package? …… Y / N

Laboratory: ………………………………………………………………………………………………

Date: …………………………………………… Signature: ………………………………..……

APPENDIX 2: RESULT REPORT OF AVERAGED LED INTENSITY (S3A)

Artefact set number:

Measurement dates: from to

Laboratory condition: temperature ( ± ) ºC , relative humidity ( ± ) %

LED

measurement value of

averaged LED intensity (cd)

expanded uncertainty* of averaged LED intensity (cd)


junction voltage (V)

expanded uncertainty* of junction voltage

(V)

total burning time (min)

R-1

R-2

R-3

G-1

G-2

G-3

B-1

B-2

B-3

W-1

W-2

W-3

D-1

D-2

* estimated for a 95 % confidence level (normally with a coverage factor k = 2)

Laboratory: ………………………………………………………………………………………………

Date: …………………………………………… Signature: ………………………………..……

APPENDIX 3: RESULT REPORT OF TOTAL LUMINOUS FLUX (S3B)




LED

measurement value of total luminous flux

(lm)

expanded uncertainty* of total luminous

flux (lm)



expanded uncertainty* of junction voltage

(V)

total burning time (min)

R-1

R-2

R-3

G-1

G-2

G-3

B-1

B-2

B-3

W-1

W-2

W-3


Laboratory: ………………………………………………………………………………………………

Date: …………………………………………… Signature: ………………………………..……

APPENDIX 4: RESULT REPORT OF EMITTED COLOUR (S3C)




measurement value of chromaticity

coordinate

expanded uncertainty* of

chromaticity coordinate LED

x y x y



expanded uncertainty* of junction voltage (V)

total burning

time (min)

R-1

R-2

R-3

G-1

G-2

G-3

B-1

B-2

B-3

W-1

W-2

W-3

D-1

D-2


Laboratory: ………………………………………………………………………………………………

Date: …………………………………………… Signature: ………………………………..……

Summary of Comments in Review of Relative Data

VSL

Mail on Dec 14, 2009

Looking to the data of VSL we see a big instability for some of the LEDs. Can you tell me how

you are going to deal with this and what the effect will be for the KCRV values or final

presentation of the results?

Response of KRISS on Dec 22, 2009

I think the stability for the LEDs used for VSL is not so bad (all below 1 % drift). I propose to

average the LEDs of the same type (three of red, three of green, etc.) and take the instability as an

uncertainty component of the difference from the reference value. (There will be no KCRV and

DoE because these are supplementary comparisons.)

Of course, we will exclude particular LEDs which show bad stability based on the opinion and

agreement of the participant.

Mail on March 17, 2010

Looking to the remarks of the temperature correction data we are wondering if the inconsistence

for some of the data has to do with the measurement of the junction voltage. As I can remember

there was a relative large variation in voltage over the legs of the LEDs. So in some cases

depending on the position of the junction measurement this can affect the correction for

temperature. Of course one needs to take this variation into the uncertainty for the voltage

measurement at the junction but maybe some of the inconsistencies can be explained looking to

the uncertainty for junction measurements versus temperature correction and the variation of

junction voltage over the legs of the LEDs.

Response of KRISS on March 24, 2010

It is true that there is a change of junction voltage when the measurement position of the LED

electrodes changes. We have noticed this at the stage of the artefact preparation, and therefore

arranged that this variation due to the junction position should be checked and reported by each

participant as an uncertainty component of junction voltage.

Because we have all the sensitivity data of photometric quantity to junction voltage for each

artefact LED, we can analyze the inconsistency caused by the inaccurate measurement of junction

voltage. We will surely include this in the result report. From our experience, however, the

uncertainty of photometric quantities propagated from the uncertainty of junction voltage

measurement, including the junction position variation, was much lower than 0.5 %, which is the

principal accuracy limit of the temperature correction method via junction voltage.

METAS

Mail on Dec 15, 2009

I have no special observation.

Mail on Feb 10, 2010

I have no special comments in respect to our relative data except that applying the temperature

correction will increase non-consistency of our data. I’ve done this analysis for all participants (see

enclosed excel-file) and it is interesting to see that only for few laboratories the consistency

increases.

Response of KRISS on Feb 12, 2010

You showed that the consistency decreases after the temperature correction, i.e. the standard

deviation of all the relative data for a participant increases. I think this is reasonable because the

process of temperature correction contains also the uncertainty, which is the limitation of the

theoretical model for temperature correction via junction voltage. We estimate this uncertainty to

be less than 0.5 % (see our publication in Metrologia, 43, 299, 2006). Therefore, we expect that

the application of temperature correction unavoidably causes a slight decrease of the consistency

of the relative data. Based on your calculation, the standard deviations of the relative data lie, for

most of the participants, between 0.5 % and 1 % without temperature correction, but the

(absolute) change of them due to temperature correction remains much below 0.5 %. From this,

we can confirm the accuracy of the temperature correction method.

In addition, we could also see the validity of temperature correction in the change of the absolute

data (not published yet) that the consistency between the pilot and the participants clearly

increases after temperature correction.

MKEH

Mail on Jan 20, 2010

After the overview of the MKEH relative data of the comparisons APMP-S3a (averaged LED

intensity) we have two remarks:

The LED G1, which was strongly different, died after the MKEH measurement. So this diode does

not have remeasured value. It might be damaged before the MKEH measurement. We ask for

remove the data of this diode.

The LED B3, which was different as well, died after the MKEH measurement. So this diode does

not have remeasured value. It might be damaged before the MKEH measurement as well. We ask

for remove the data of this diode.


We accept the data you have sent. (with respect to S3c)

MIKES


Could we remove the W-1 LED from the both comparisons?

NIST


We think that the LED set measured by NIST was not so bad if KRISS' measurement results for R1

and R2 were reliable. So we want to confirm that the differences (shown in your relative data)

between the measurement results of R1 and R2 are acceptable to us.

NMIJ

Mail on Dec 28, 2009 (not delivered in time)

By the way, it is the matter of review of relative data, in order to estimate whether it is drift of

LEDs, I would like to know the information of total burning time of our artifact(set #4) including

measurement burning time in KRISS.

I know the burning time in our measurement, but I don't know it in KRISS.

In addition, I would like to know about the seasoning result of our artifact.

Unless KRISS clarifies these information, it is very difficult to judge against our result of relative

data whether it is a drift of LEDs or some issue.


I would like to request to remove the result of B-1, B-3, W-1 from our APMP.PR-S3a results. In

addition, I would like also to request to remove the result of W-1 from our APMP.PR-S3b results.

Because, I think that the change of those LED result is large.

ASTAR


Thanks for the relative data. We have reviewed the data. The data looks in order and we have not

further comments for the relative data of all three comparisons.

Summary of Comments in Review of Uncertainty Budgets

Part 1. General Comments and Revisions

INM (Romania)

Mail on April 02, 2010

As far as the INM reports are concerned, the uncertainty budgets for Green, Blue, White and

Diffuse LEDs were not included in the APMP PR S 3a and APMP PR S3b reports just because they

are very close to our uncertainty budgets for the Red LEDs so we thought not necessary to repeat

the almost exactly same figures. But do you think this is necessary or should we merely mention

this in the reports? Anyway, in order to comply I`ll revise and sent you our reports today, provided

it`s not already too late.

Here attached are our revised reports for APMP PR S3a and APMP PR S3b comparisons, incliding

the uncertainty budgets for all tipes of LEDs.

Please notice that changes only concerned the spectral correction factors for the various LEDs and

while the combined standard uncertainties were of about 5.5 %, the various spectral correction

factors induced quite small changes (less than +/- 0,5 %) in the combined uncertainties values.

That`s why, initially we only reported the uncertainty budgets for the red LEDs.

Response of KRISS on April 12, 2010

I have properly received your two documents including the uncertainty budgets for all color-types

of LEDs. The formats you sent me are ok.

Because your revision deals only with an addition of information, I see no problem to accept your

revision for the report. I will wait for a while for other revisions or corrections, and distribute the

revised files then.

METAS

Mail on April 15, 2010

Please find enclosed an update of our description of the uncertainty budget of the chromaticity

coordinates. I’m sorry to have it sent after your deadline. In the updated version I stated explicitly

uncertainty budgets for the 4 types of LEDs. It’s just to give more information, no value has been

changed.

I also would like to recall our worries in respect to the correlation of chromaticity coordinates (see

the attached file).

APMP.PR-S3 Correlation of chro

Response of KRISS on April 15, 2010

I have received your files well. I will revise the uncertainty review document for S3c and distribute

it again. (But I will wait for a while to collect the revisions also from other participants.)

I think that your suggestion of reporting the correlation can be discussed open. Do you agree to

forward your document directly to all the participants to ask for their opinions?

A*STAR

Mail on June 21, 2010

We found not error in the three files containing technical information and uncertainty budgets.

However we added a paragraph in section 10.3 (in red colour text) of the “uncertainty

budgets_S3b” to mention the absorption correction in integrating sphere calibration and

measurement. The modified file is attached.

All Participants (open discussion)

Mail from KRISS on May 10, 2010

I have a comment which is sent from METAS to all the participants. Peter agreed to discuss this

issue openly.

This deals with a suggestion that, for the uncertainty budgets of chromaticity coordinates (x, y) for

APMP-S3c, the correlation between u(x) and u(y) should be considered by submitting the

correlation coefficient u(x,y)/u(x)u(y). Please see also the attached letter from Peter.

I personally think that it is meaningful to compare also the correlation coefficients among the

participants. However, it may be difficult at this stage to make the report of the correlation

mandatory because we did not mention this in the technical protocol. What we can do instead is

to encourage the participants to voluntarily report the correlation analysis as far as possible. If we

have many volunteers, we can include this part in the comparison report. If we have only a few

participants reporting the correlation, we can prepare this issue to an extra publication.

I would like to ask first who can submit the results of the correlation coefficients for the

chromaticity coordinates as supplementary to the uncertainty budget report. (METAS surely, and

KRISS can also do it.)

Mail from PTB on May 12, 2010

Correlation (x,y): If needed we can add the correlation of (x,y). Please let us know what is the

decision.

Mail from A*STAR on June 21, 2010

Regarding the issue our response is that we cannot submit the correlation coefficients for the uncertainty of the chromaticity coordinates.

Communication from KRISS on June 21, 2010

Typical values of correlation coefficient r(x,y) = u(x,y)/u(x)u(y) are -0.69 for RED, +0.41 for GREEN, -

0.86 for BLUE, and +0.96 for WHITE. The values do not change much as the artifact set changes.

Part 2. Questions and Answers

KRISS

Question to KRISS on May 10, 2010

-S3a average LED intensity

What are the uncertainty of the axis alignment (angular, translational) and distance: expressed in °

and mm?

-S3c, chromaticity coordinates, red LED

For the red LED the main contribution of the uncertainty is given by the spectral straylight. Has

the data been corrected for straylight? Why the contribution for red is much large then for the

others (red x: 0.00148, blue x: 0.00032) and why x and y are so different (usually there is full

correlation for the chromaticity coordinates for red LEDs).

-S3c, chromaticity coordinates, wavelength

For the other LED’s the main contribution of the uncertainty is given by the wavelength accuracy.

It would be useful to know the absolute uncertainty of the wavelength scale (expressed in nm).

Have there been some spectral correlations taking to account in the analysis?

Answers from KRISS on June 21, 2010 -S3a average LED intensity What are the uncertainty of the axis alignment (angular, translational) and distance: expressed in ° and mm? Response: The standard uncertainty of angular axis alignment, translation axis alignment, and distance setting is 0.82°, 0.41 mm and 0.25 mm, respectively. For translational axis alignment, the uncertainty contribution has been revised such as 0.2 % for red (Other else remain the same). -S3c, chromaticity coordinates, red LED For the red LED the main contribution of the uncertainty is given by the spectral stray light. Has the data been corrected for stray light? Why the contribution for red is much large then for the others (red x: 0.00148, blue x: 0.00032) and why x and y are so different (usually there is full correlation for the chromaticity coordinates for red LEDs). Response: The spectral stray light of spectral data is not corrected. We estimated the spectral stray light as an uncertainty based on the spectrograph response under He-Ne laser illumination. Most of stray light readout is distributed around the laser wavelength except the in-band region, which means that the spectral stray light has a similar spectral distribution with the input illumination. Thus, the contribution of the stray spectrum on chromaticity is more or less proportional to that of the input illumination. While the stray spectrum gives more contribution to x in case of a red LED, the stray spectrum of a green LED and a blue LED give more contribution to y and z, respectively. In our calculation, the correlation coefficient r(x, y) of a red LED turned out to -0.69. -S3c, chromaticity coordinates, wavelength For the other LED’s the main contribution of the uncertainty is given by the wavelength accuracy. It would be useful to know the absolute uncertainty of the wavelength scale (expressed in nm). Have there been some spectral correlations taking to account in the analysis? Response: The standard uncertainty of wavelength scale is (0.45 ~ 0.48) nm depending on wavelength. Of the uncertainty,

0.2 nm is a global wavelength offset, which mainly contributes on the chromaticity uncertainty. The spectral correlations are taken account in.

MIKES

Question to MIKES on May 10, 2010


The uncertainty is by far dominated by the repeatability of the measurement. What is the origin of

this? Were measurement noisy? In the case of the diffuse type LED this contribution is smaller

than for the other type. Is it related to the geometry of the source? Is it really repeatability and

not reproducibility (i.e. were the LED realigned?)?

-S3b, luminous flux

The most important contribution (expect for the blue LED) originates from the near field

absorption (1%, with rectangular distribution!). How this value has been determined?

-S3c, chromaticity coordinates, white LED, angular alignment

The uncertainties of the chromaticity coordinates of the white LED are much higher than the other

coloured LEDs (except to the one with diffuser). The main contribution seems to be originated for

the angular alignment, although the sensitivity coefficient of that quantity seems to be the similar.

What is the origin of this?

-S3c, chromaticity coordinates, green LED

The uncertainty of the green LED with diffuser is dominated by the noise. How this contribution

has been determined as it as of Type B with rectangular probability? Usually noise contributions

are included in the repeatability of the measurement (Type A).

Answers from MIKES on May 31, 2010 > /-S3a average LED intensity / > > The uncertainty is by far dominated by the repeatability of the > measurement. What is the origin of this? Were measurement noisy? In > the case of the diffuse type LED this contribution is smaller than for > the other type. Is it related to the geometry of the source? Is it > really repeatability and not reproducibility (i.e. were the LED > realigned?)? > Answer: The uncertainty of repeatability originates mainly from the alignment accuracy of the measurement setup, i.e. the realignment of the LED before each repeat measurement. For the diffuser type of LEDs, the uncertainty due to the alignment was not found as sensitive as for the other type of LEDs. This could be partly explained by the optical properties of the measured LEDs. The LEDs without diffusing output may have nonuniform structure in the light output. > > /-S3b, luminous flux/ > > The most important contribution (expect for the blue LED) originates

> from the near field absorption (1%, with rectangular distribution!). > How this value has been determined? > Answer: The uncertainty of the near field absorption (type B) was estimated by considering the geometry and materials used in the LED holder and the amount of light emitted backward by the measured LEDs. > /-S3c, chromaticity coordinates, white LED, angular alignment/ > > The uncertainties of the chromaticity coordinates of the white LED are > much higher than the other coloured LEDs (except to the one with > diffuser). The main contribution seems to be originated for the > angular alignment, although the sensitivity coefficient of that > quantity seems to be the similar. What is the origin of this? > Answer: In the case of white LEDs, the spectral output may change as a function of angle of observation due to the phosphor coating. Therefore they are more sensitive to the alignment than the other type of LEDs. > /-S3c, chromaticity coordinates, green LED/ > > The uncertainty of the green LED with diffuser is dominated by the > noise. How this contribution has been determined as it as of Type B > with rectangular probability? Usually noise contributions are included > in the repeatability of the measurement (Type A). > Answer: The uncertainty of the diffuser type of LED was obtained by calculating the color coordinates for the original measurement data and for another data, in which the noise of the low signal values was replaced with extrapolated modelled values of the measured LED spectrum.

CMS-ITRI

Question to CMS-ITRI on May 10, 2010

-S3a average LED intensity, LED spatial light distribution

Why the quantity “LED spatial light distribution” is the same for all type of LEDs even the spatial

distribution is very different for the different LEDs (in particular the one with diffuser to the one

without diffuser)

-S3a average LED intensity, red LED,

The uncertainty of the spectral mismatch correction seems to be exceptionally small for the red

LED in respect to the other colours. What is the f1’ of the photometer?


The uncertainty of the “x” - chromaticity coordinate of the red LED is dominated by two

contributions (repeatability :0.0015 and mechanical alignment: 0.0014). Why the combined

uncertainty is only 0.0014?

-S3c, chromaticity coordinates, mechanical alignment

why the uncertainty contribution due to mechanical alignment is the same for all type of LEDs? Is

there an evidence that a misalignment causes the same amount of shift in colour coordinates?

-S3c, chromaticity coordinates, green LED and green LED with diffusor

why the contribution of the wavelength shift of the green LED with diffusor is much higher than

the green LED without diffuser (more than 20x), the spectral distribution of both type of LEDs

being very similar?

PTB

Question to PTB on May 10, 2010


It would be interesting to know the area of the sensitive surface of the photometer head, and in

the case that it is different to 100mm2 how that results were corrected.

-S3a average LED intensity, Correction for LED angular align,

Why the uncertainty due to the correction for angular alignment of the blue LED (0.57%) is much

larger than for the other LEDs (green: 0.11%) although the spatial distribution of is very similar?

-S3b, luminous flux, Integrated photocurrent, solid angle weighted

The most important contribution of uncertainty is originated from the quantity “Integrated

photocurrent, solid angle weighted”. It would be useful to have further information about this

quantity (i.e. eventl. citation). How it has been determined?


The uncertainty of the chromaticity coordinates of the red LED is mainly given by the spectral

bandpass correction and the straylight correction of the spectrometer. There is however no

information about the amount of correction that has been applied and the spectrometer used for

the measurement(bandpass, wavelength accuracy, level of straylight,…)

-There is no information about the uncertainty contributions (input quantities and their

uncertainties) used in the Monte Carlo simulation.

Answers from PTB on May 12, 2010 Here are the answers of PTB concerning some questions of a participant: -S3a average LED intensity It would be interesting to know the area of the sensitive surface of the photometer head, and in the case that it is different to 100mm2 how that results were corrected. PTB: According to CIE Pub. 127 in all cases (S3a, S3b and S3c) the sensitive area of photometers or spectrometer input optics were 100 mm2. So no corrections for a different sensitive area were applied.

-S3a average LED intensity, Correction for LED angular align, Why the uncertainty due to the correction for angular alignment of the blue LED (0.57%) is much larger than for the other LEDs (green: 0.11%) although the spatial distribution of is very similar? PTB: From goniophotometric luminous flux measurements we know the spatial distribution of all LEDs. Especially the spatial distribution of green and blue LEDs are not similar in the interesting range of approx. 0° < ϑ < 2.5° ! Please, see figures below (on the left: example of green LED, on the right: example of blue LED). We describe the spatial distribution with cos[ϑ]g. In case of the green LED we found g=8.9 and in case of the blue LED we found g=39. Please, compare blue plots.

Now we are able the estimate the uncertainty contribution of angular alignment and translational alignment of the LED for luminous intensity measurements by help of a mathematical simulation. The figure below on the left shows a LED aligned in front of a photometer. The angular and aerial responsivity oft he photometer is simulated by a number of hexagons. For our estimations we used a larger number of smaller hexagons (see figure on the right). Based on the knowledge of uncertainty for angular alignment and translational alignment we are able to calculate the estimated uncertainty contributions.

Total area = 100 mm2

5

10

15

20

2530

3540

4550

5560

6570758085

0.2 0.4 0.6 0.8 1.0

0.2

0.4

0.6

0.8

1.0

LEDG101.evk, redmeasured datablueFit Cosg with g8.92036, dashedCos

5

10

15

20

25

30

3540

4550

5560

6570758085

0.2 0.4 0.6 0.8 1.0

0.2

0.4

0.6

0.8

1.0

LEDB101.evk, redmeasured datablueFit Cosg with g39.0866, dashedCos

-S3b, luminous flux, Integrated photocurrent, solid angle weighted The most important contribution of uncertainty is originated from the quantity “Integrated photocurrent, solid angle weighted”. It would be useful to have further information about this quantity (i.e. eventl. citation). How it has been determined? PTB: The figure below on the left shows the goniophotometric measurement of the LEDs in principle. The averaged zonal illuminance is derived from the measured averaged zonal photocurrent ( )ϑj . The figure on the right shows it as a function of the angle ϑ .

Since the determination of this averaged zonal photocurrent is a complex system which consists of several dc motor drives, a current/voltage converter and a digital voltmeter a correction factor czone

was introduced. The averaged value of czone = 1, but to consider the uncertainty caused by an

unsharp start and stop angle ( EndStart ϕϕ , ) it is necessary and defined as follows :

πϕϕ

2EndStart

zonec −=

Now we can start the MC-simulation: Repeat the following with normal distributed varied KVVEndStart j,,, ϑϕϕ

( ) ( ) ( ) ϑϑϑϑϑπ

ϑ

d1Sin0

zone ⋅+⋅+⋅+⋅= ∫=

KVVV jjcX

and in principle from X you will get the so called “Integrated photocurrent, solid angle weighted”

( )Xj Mean=Φ with ( ) ( )XU j viationStandardde=Φ .

-S3c, chromaticity coordinates, red LED The uncertainty of the chromaticity coordinates of the red LED is mainly given by the spectral bandpass correction and the straylight correction of the spectrometer. There is however no information about the amount of correction that has been applied and the spectrometer used for the measurement(bandpass, wavelength accuracy, level of straylight,…) -There is no information about the uncertainty contributions (input quantities and their uncertainties) used in the Monte Carlo simulation.

0.5 1.0 1.5 2.0 2.5 3.0Radian

2.107

4.107

6.107

8.107

Photocurrent AMeasured averaged zonal photocurrent as function of zone angle

PTB: As you can see in our uncertainty budgets the correction values of bandpass and spectrometer straylight is always 0. That means no correction was applied. But we estimated the uncertainty contributions by help of some MC simulations. The following figure shows an example result of a similar simulation.

Varied input parameters of the simulation were mainly spectrometer response data during measurement the LED and the halogen lamp used for sensitive calibration with an uncertainty of their spectral irradiance expressed as an uncertainty of the distribution temperature of a planckian radiator (approx. 10 K), an estimated straylight correction matrix (similar to the figure below, which is the real strayight correction matrix of the used array spectrometer from knowledge we have today ), an assumed triangle-shaped bandpass (halfwidth approx. 3nm ), the function between channel-no and wavelengths with a wavelength uncertainty of approx. 0.8nm, etc.

NMIJ

Question to NMIJ on May 10, 2010

0.6998 0.7002 0.7004 0.7006x

0.2988

0.2992

0.2994

0.2996

y

500 500

1000 1000

-S3a average LED intensity, illuminance responsivity

It is very unusual to see a rectangular probability function for the uncertainty of the illuminance

responsivity. Usually this value is either taken from a calibration certificate or determined by

another measurement (traceable to the radiometric scale). In both cases the distribution is

typically Gaussian type. Furthermore the uncertainty seems to be rather large (much larger than

declared CMC values in the KCDB with k=2…).

-S3b, luminous flux, Angular resolution, etc.

Why the contribution of the quantity called « angular resolution, etc » is much larger for the red

LED than for the others (red: 0.91%, green: 0.28%) even if the angular distribution of the LEDs are

very similar (the green LED is even narrower than the red)?


It would be useful to report in the uncertainty budget of the chromaticity coordinates of the red

LED one additional digit (in the column “contribution”). The GUM recommands to report

uncertainty with two significant digit.

Answers from NMIJ on June 02, 2010

I am submitting two file (Reply to Question and Revised verification report).

Revised points in verification file are edited the Word files with red characters. New verification

report is revised according to the comment (Uncertainty Component name, Deg. of freedom, add

to new figure etc,).

But, there is no modify of the combined standard uncertainty .

Q1:-S3a average LED intensity, illuminance responsivity

It is very unusual to see a rectangular probability function for the uncertainty of the illuminance

responsivity. Usually this value is either taken from a calibration certificate or determined by

another measurement (traceable to the radiometric scale). In both cases the distribution is

typically Gaussian type. Furthermore the uncertainty seems to be rather large (much larger than

declared CMC values in the KCDB with k=2…).

Re1:

Thank you for good advice. I made a mistake about probability function of illuminance

responsivity. I would like to correct about probability function and freedom of it.

Next, I would like to explain about uncertainty of illuminance responsivity. In order to consider a

near-field effects which CIE 127:2007 (5.4 P17) described, illuminance responsivity of our

photometer for LED measurement is calibrated by luminous intensity standard lamp at far-field

condition, and then it is calibrated by an integrating sphere source(operated at 2856K) at the

distance corresponding to CIE condition B. Our uncertainties of illuminance responsivity include

uncertainty of near-filed effect. Therefore it becomes larger than uncertainty of CMC.

Q1:-S3b, luminous flux, Angular resolution, etc.

Why the contribution of the quantity called ≪ angular resolution, etc ≫is much larger for the

red LED than for the others (red: 0.91%, green: 0.28%) even if the angular distribution of the LEDs

are very similar (the green LED is even narrower than the red)?

Re2:

Firstly, I would like to change the contribution of the quantity's name from "angular resolution,

etc" to "measurement angle step and angular resolution". I send the modified uncertainty budget.

Sorry, my expressions confuse.

Fig1 indicate an angular distribution of red and green LED. The angular distributions of red LED

is not smoother than it of green LED .I think the angular distribution of the red LED is not the

same as others. Red LED have an irregular angular distribution. For this reasons, the uncertainty of

"measurement step and angular resolution" on red LED became larger than green LED in our

budget.

Fig1: angular distribution

Q3:-S3c, chromaticity coordinates, red LED

It would be useful to report in the uncertainty budget of the chromaticity coordinates of the red

LED one additional digit (in the column "contribution”). The GUM recommends reporting

uncertainty with two significant digits.

A3:

Thank you for good advice. I send the modified uncertainty budget. I add one additional digit to

uncertainty values of contribution, but the combined standard uncertainty isn't changed.

CENAM

Question to CENAM on May 10, 2010

-S3a, average LED intensity, Spectral mismatch correction

Why the uncertainty of the spectral mismatch correction is almost constant for all type of LED’s?

Usually the uncertainty is much lower for white LEDs than for blue LEDs?

-S3b, luminous flux, Standard lamps spectral mismatch correction

The quantity “Standard lamps spectral mismatch correction” seems to be rather large. What kind

of standard lamps was used (usually incandescent lamps are used which are not too far from CIE

illuminant A)? What is the f1’ value of the photometer? What is the estimated relative spectral

throughput of the sphere (i.e. how “flat” is the painting)?

-S3c, chromaticity coordinates

What is the quantity “Propagation from spectral distribution measurement”? Why is it constant for

all colours (15.66% , 13.96%) and why the sensitivity coefficient so small 0.00002 (% per %?) and

constant?


uncertainty of chromaticity coordinates are usually reported as absolute value as chromaticity

coordinates are highly non-linear quantities.


in the case of the red LED the absolute uncertainty are as following: ux= 0.006 and uy=0.0006

(hence a factor of 10 between both coordinates). Is there are an explication for this behavior?

Usually the chromaticity of red LED are fully (negative) correlated resulting in similar uncertainties

in x an y?

Answers from CENAM on May 20, 2010

Please find below the answers to the questions done for CENAM. -S3a, average LED intensity, Spectral mismatch correction

Why the uncertainty of the spectral mismatch correction is almost constant for all type of LED’s?

Usually the uncertainty is much lower for white LEDs than for blue LEDs?

RE: Unfortunately the resolution of the spectrorradiometer we used to measure the LEDs spectra was very bad; thus causing this component to be dominant over the other, and making the spectral mismatch uncertainties to look almost constant.

-S3b, luminous flux, Standard lamps spectral mismatch correction

The quantity “Standard lamps spectral mismatch correction” seems to be rather large. What kind

of standard lamps was used (usually incandescent lamps are used which are not too far from CIE

illuminant A)? What is the f1’ value of the photometer? What is the estimated relative spectral

throughput of the sphere (i.e. how “flat” is the painting)?

RE: Unfortunately the resolution of the spectrorradiometer we used to measure the spectra was very bad; thus causing this spectral mismatch corrections to be very large. We used incandescent lamps operated as CIE Standard illuminant A. The f1=13,36. The estimated relative spectral throughput of the sphere is fairly plain.


What is the quantity “Propagation from spectral distribution measurement”? Why is it constant for

all colours (15.66% , 13.96%) and why the sensitivity coefficient so small 0.00002 (% per %?) and

constant?

RE: We call “Propagation from spectral distribution measurement” to the uncertainty component due to the calculation method from the spectral irradiance lectures. This is constant because we used the average value obtained from the standard lamps used. This also produced such a sensitivity coefficient values, and almost constants.




RE: We reported our final results for those values as absolute to the pilot laboratory; however, according to the final report format, we were requested to report those as relative, and we did it as well.


in the case of the red LED the absolute uncertainty are as following: ux= 0.006 and uy=0.0006

(hence a factor of 10 between both coordinates). Is there are an explication for this behavior?

Usually the chromaticity of red LED are fully (negative) correlated resulting in similar uncertainties

in x an y?

RE: We do not find such a values as they are mentioned. We have double-checked the results we send to the pilot laboratory; as well as those the pilot laboratory sent back for revision; and we found they are ok, within the same magnitude order. Would you please let us know where you found those?

LNE

Question to LNE on May 10, 2010




NMC-A*STAR

Question to A*STAR on May 10, 2010

-S3b, luminous flux,

A*STAR has not used an auxiliary lamp for compensating changes of the integration properties of

the sphere resulting in the different configuration between the LED measurement and the sphere

calibration. Has this influence being estimated?




Answers from A*STAR on June 21, 2010

Question for: -S3b, luminous flux, A*STAR has not used an auxiliary lamp for compensating changes of the integration properties of the sphere resulting in the different configuration between the LED measurement and the sphere calibration. Has this influence being estimated? Reply: The one-meter integrating sphere that we used for LED flux measurement do have a tungsten auxiliary lamp. The absorption corrections were carried out over the whole wavelength range of 380 nm to 780 nm in 1 nm interval for both the LED measurement and the sphere calibration. An additional paragraph explaining this is added in section 10.3 of the uncertainty budgets_S3b. Please refer to the revised file attached. (Dong-Hoon, the revised file is actually attached in my last email to you so I didn’t repeat here) Question for: -S3c, chromaticity coordinates uncertainty of chromaticity coordinates are usually reported as absolute value as chromaticity coordinates are highly non-linear quantities. Reply: The uncertainty of chromaticity coordinates that we reported for the -S3c results are indeed in absolute values.

VSL

Question to VSL on May 10, 2010

-S3a, average LED intensity

What is the quantity “Non-uniformity of source”? Is this due to the non-coincidence of the optical

and mechanical axis? In Figure 11-6 of the report a measurement of the illuminance in function of

different (azimuthal) angles is shown. It is written that this is due to the non-coincidence of the

mechanical axis and the optical axis. However we believe that it is to a misalignment of the

photometer in respect to the rotation axis as illustrated below.

-S3b, luminous flux, Near-field absorption of backward emission

The most important contribution to uncertainty is the quantity “Near-field absorption of backward

emission”. Has the flux also being corrected with this quantity, if yes what was the estimated ratio

from the backwards flux to the total flux?

-S3b, luminous flux

The goniophotometrical measurements were done at an angular increment of 5° (polar angle).

Has the uncertainty due to this rather large increment been estimated (The half angle of the

green LED is only 22°)?

Answers from VSL on May 10, 2010 -S3a, average LED intensity What is the quantity “Non-uniformity of source”? Is this due to the non-coincidence of the optical and mechanical axis? In Figure 11-6 of the report a measurement of the illuminance in function of different (azimuthal) angles is shown. It is written that this is due to the non-coincidence of the mechanical axis and the optical axis. However we believe that it is to a misalignment of the photometer in respect to the rotation axis as illustrated below. Answer VSL As the reference axis for alignment is not defined in the protocol, one needs to make a choice which axis is used for alignment (optical or mechanical). From our research we believe that the mechanical axis for alignment is the best choice for comparability of the measurement results. When using the mechanical axis as a reference axis you will need to check what this means with respect to the azimuthal angle direction in respect to the uncertainty. As measurements show (figure 11-6 of the report) one needs to take the non-coincidence of the mechanical and optical axis into account, again: if you are using the mechanical axis as reference. Please notice that when you align on optical axis you will introduce an angular shift between the optical axis of your LED and the rotation axis of your goniometer. This will also introduce an uncertainty. -S3b, luminous flux, Near-field absorption of backward emission The most important contribution to uncertainty is the quantity “Near-field absorption of backward emission”. Has the flux also being corrected with this quantity, if yes what was the estimated ratio from the backwards flux to the total flux?

Answer VSL The flux has not been corrected for the “Near-field absorption of backward emission”.

-S3b, luminous flux The goniophotometrical measurements were done at an angular increment of 5° (polar angle). Has

the uncertainty due to this rather large increment been estimated (The half angle of the green LED is only 22°)?

Answer VSL As the detector size of our photometer is 10 mm^2 one can calculate the smallest step size that is required to have overlap between the measurement points measuring at a distance of 100 mm. With a step size of 5º we still have an overlap from point to point. Next to this we have taken the green LED and measured ones in steps of 5º and ones in steps of 1º. The results showed that there is a small difference in respect to the total uncertainty between a step of 5º compared to a step size of 1º. We have taken the difference into the uncertainty component for the integration method.

NIST

Question to NIST on May 10, 2010


What is the estimated wavelength uncertainty of the spectrometer measurement (expressed in

nm)? Have there been some spectral correlations taking to account in the analysis?

-S3c, chromaticity coordinates, contributions due to alignment of the LED

Minor comment: It is very unusually that Type A has an infinite number of degree of freedom.

Either the contribution has been determined experimentally and then a statistics is used (Type A

with limited number of degrees of freedom) or a model was used (perhaps also based on

experimental results) to describe the specific input quantity (Type B with infinite number of

degrees of freedom).

MKEH

Question to MKEH on May 10, 2010

-S3a, average LED intensity

Several important contributions are missing: temperature, readout of the photometer (Type A).

Why the calibration accuracy has a rectangular distribution, usually it should be Gaussian

distributed.


Why the uncertainty is stated as a minimum value (>0.0004 and >0.0002). The uncertainty analysis

is used to determine the estimates of the output quantity and its uncertainty (for a given

confidence interval). If only a minimum value is stated either the uncertainty budget is incomplete

or the estimation of some of the contributions are believed to be too small (and should therefore

be adapted).

Answers from MKEH on June 1, 2010

1. In the luminous intensity error budget our main source of error comes from the detector

calibration. We do not have cryogenic radiometer we have Si selfcalibration as an absolute

method. In this case the main source of error is not statistical, but the practical uncertainty of the

method (the internal QE is not measured just believed, based on the literature).

Therefore this is a type B error. All the other participants have cryogenic radiometer……

2. In the color uncertainty budget I have left out data. YOU ARE right…

Revised budget:

source of uncertainty

standard uncertainty

probability distribution

sensitivity coefficient

standard uncertainty in

∆x

standard uncertainty in

∆y spectral

irradiance calibration

1,5% rectangular type B

sample dependent

∆x1 <0,002 0,0003 < ∆x1

∆y1 <0,002 0,0001 < ∆y1

wavelength error 0,1 nm rectangular

type B sample

dependent ∆x2 <0,001

0,00005 < ∆x2 ∆y2 <0,001

0,00005 < ∆y2

linearity 0,05% rectangular type B

sample dependent

∆x3 <0,0005 0,00005 < ∆x3

∆y3 <0,0005 0,00005 < ∆y3

stray light 10-15 – 10-13W rectangular type B

sample dependent

∆x4 <0,0014 0,00005 < ∆x4

∆y4 <0,002 0,00005 < ∆y4

dark noise 2*10-15 W rectangular type B

sample dependent

∆x5 <0,002 0,00003< ∆x5

∆y5 <0,003 0,00001 < ∆y5

room temp. dependence 1 K rectangular

type B sample

dependent ∆x6 <0,00005 ∆y6 <0,00005

light source repeatability as measured normal

type A sample

dependent as calculated as calculated

geometry error rectangular type B

sample dependent as calculated as calculated

combined standard

uncertainty 0,0004 < ∆x

∆x < 0,0026 0,0002 < ∆y ∆y < 0,0032


LED Measurements




Identification of Outliers

1. INTRODUCTION

The relative deviations from the mean value are calculated for each participant and for each type of LEDs and distributed in order to identify the obvious outliers, which can significantly skew the Reference Values of the comparison. Each participant should recommend which data should be removed in the calculation of the Reference Values. The name of the participant is not disclosed in this stage.

The relative deviations from the mean value are obtained as follows:

1. The ratios r1(Xi) and r2(Xi) are calculated for each artefact LED (Xi = R-i, G-i, B-i, W-i, or D-i with i = 1, 2 or 3):

1 21 2

( ) ( )( ) ; ( )( ) ( )

L i L ii i

P i P i

y X y Xr X r Xy X y X

= = . (1)

Here, yL(Xi), yP1(Xi), yP2(Xi) denote the measurement result of the participant laboratory, of the pilot laboratory before travel, and of the pilot laboratory after travel, respectively, for the artefact LED Xi.

2. The difference of the ratios corresponding to the artefact drift is calculated for each artefact LED Xi:

2 1( ) ( ) ( )i i id X r X r X= − . (2)

3. The mean value of each type of LEDs is calculated for each type of the artefact LEDs:

,

,

,

,

,

( ) ( ) ,

( ) ( ) ,

( ) ( ) ,

( ) ( ) ,

( ) ( ) .

i j i j

i j i j

i j i j

i j i j

i j i j

m R Mean r R

m G Mean r G

m B Mean r B

m W Mean r W

m D Mean r D

=

=

=

=

=

. (3)

Here, the following data are excluded in the calculation of the mean: firstly, the data which are requested to be removed by the participant in the process of review of relative data, secondly, the data with its drift in Eq. (2) larger than 4 % after the temperature correction.

Note that the mean values of the ratios in Eqs. (3) correspond to the relative deviations of the participant’s data with respect to the pilot’s data.

4. The mean values in Eqs. (3) are normalized to the mean value of the measurement data of all the participants for the same type of the artefact LEDs:

[ ]

[ ]

[ ]

[ ]

[ ]

( )( ) ,( )

( )( ) ,( )

( )( ) ,( )

( )( ) ,( )

( )( ) .( )

Lab xLab x

Lab n n

Lab xLab x

Lab n n

Lab xLab x

Lab n n

Lab xLab x

Lab n n

Lab xLab x

Lab n n

m RM RMean m R

m GM GMean m G

m BM BMean m B

m WM WMean m W

m DM DMean m D

−−

−

−−

−

−−

−

−−

−

−−

−

=

=

=

=

=

(4)

5. The deviations of the mean values in Eqs.(4) from 1 are calculated for each participant and for each type of the artefact LED:

( ) ( ) 1,( ) ( ) 1,( ) ( ) 1,( ) ( ) 1,( ) ( ) 1.

Lab x Lab x

Lab x Lab x

Lab x Lab x

Lab x Lab x

Lab x Lab x

R M RG M GB M BW M WD M D

− −

− −

− −

− −

− −

∆ = −∆ = −∆ = −∆ = −∆ = −

(5)

Note that the deviations in Eq. (5) correspond to the relative deviations of each participant from the mean value over all the participants for each type of the artefact LEDs.

In the case of the LED measurement, the quantity to be measured is a function of junction temperature. Therefore, the junction voltage is simultaneously measured and reported with the comparison quantity. Based on the reported junction voltage data and the characteristic parameters of each artefact LED determined by the pilot laboratory in the preparation stage, the measured comparison quantities can be corrected to one junction voltage.

In the following, the relative deviations in Eqs.(5) of all the participants are listed in a table and plotted for visualization. There are two sets of the data: the first set is based on the submitted measurement data without any correction. The second set is based on the data corrected to one junction voltage as a result of the temperature correction.

In the data table, the relative deviations larger than 10 % are indicated as red, which seem to be the obvious outliers. Note that we have considered here only the result data with an artefact drift much smaller than 4 %.

2. WITHOUT CORRECTION

Lab1 Lab2 Lab3 Lab4 Lab5 Lab6 Lab7

R -1.64% 1.46% -0.72% -0.05% -2.51% -33.20% 3.67%

G -1.71% 0.39% -0.88% -0.17% 1.22% -12.26% 2.89%

B -0.85% 1.12% -2.17% -1.12% 3.62% -8.63% -0.14%

W -2.23% 1.37% -0.99% 0.09% -0.26% -19.01% 1.39%

D -2.74% 0.00% -1.58% -1.68% 0.11% -14.44% 2.61%

Lab8 Lab9 Lab10 Lab11 Lab12 Lab13 Lab14 Lab15

-0.51% 0.78% 0.24% 13.76% 2.00% 6.37% -0.40% 9.09%

0.05% -0.80% 0.69% -5.44% 2.77% -2.73% 2.76% 11.52%

1.43% 0.46% 0.15% -4.45% 2.21% -9.66% 5.57% 11.60%

-0.62% -1.18% 0.18% 5.45% 2.32% 0.68% 0.98% 9.60%

-1.34% -1.68% -0.06% -0.33% 2.98% -2.96% 0.90% 17.48%

3. WITH TEMPERATURE CORRECTION

Lab1 Lab2 Lab3 Lab4 Lab5 Lab6 Lab7

R -0.02% 0.98% -1.12% 1.33% -0.98% -33.20% 3.04%

G -1.23% 0.17% -1.23% 0.04% 1.84% -12.54% 2.86%

B -0.90% 1.12% -2.31% -1.32% 3.57% -8.49% -0.16%

W -1.38% 0.94% -1.43% 0.68% 0.55% -19.32% 1.44%

D -2.36% -0.10% -1.37% -1.00% 0.72% -14.73% 2.57%

Lab8 Lab9 Lab10 Lab11 Lab12 Lab13 Lab14 Lab15

-1.75% 1.79% 1.69% 11.21% 4.15% 4.74% -1.10% 9.23%

-0.15% -0.27% 1.19% -6.28% 3.52% -3.30% 2.52% 11.64%

1.51% 0.41% 0.10% -4.43% 2.22% -9.33% 5.66% 11.45%

-1.01% -0.29% 0.90% 3.88% 3.71% -0.56% 0.89% 9.61%

-1.29% -1.08% 0.09% -1.15% 3.69% -3.16% 1.09% 15.71%


LED Measurements




Pre-draft A Process

Review of Relative Data

1. INTRODUCTION

The relative data are calculated and distributed for review to check the stability of the artefact LEDs for each participant before and after travel, and the internal consistency of the artefact LEDs measured at each participant lab.

The relative data are obtained as follows:

1. The ratio R1(Xi) and R2(Xi) are calculated for each artefact LED (Xi = R-i, G-i, B-i, W-i, or D-i with i = 1, 2 or 3)

)()()( ;

)()()(

22

11

iP

iLi

iP

iLi Xy

XyXRXyXyXR == . (1)

Here, yL(Xi), yP1(Xi), yP2(Xi) denote the measurement result of the participant laboratory, of the pilot laboratory before travel, and of the pilot laboratory after travel, respectively, for the artefact LED Xi.

2. The ratios in Eq. (1) are normalized to the mean value of the measurement data for the same type (colour) of artefact LEDs:

[ ] [ ]jiji

ii

jiji

ii XRMean

XRXrXRMean

XRXr,

22

,

11 )(

)()( ;)(

)()( == . (2)

We refer these normalized ratios r1(Xi) and r2(Xi) as to the relative data for the artefact LED Xi. Note that the normalization in Eq. (2) removes any relationship of the absolute scale of the participant laboratory and leaves only internal consistency information within the sub-set of the same LED types.

In the case of the LED measurement, the quantity to be measured is a function of junction temperature. Therefore, the junction voltage is simultaneously measured and reported with the comparison quantity. Based on the reported junction voltage data and the characteristic parameters of each artefact LED determined by the pilot laboratory in the preparation stage, the measured comparison quantities can be corrected to one junction voltage. It is expected that this temperature correction via junction voltage can improve the stability and internal consistency of the artefact LEDs.

In the next chapters, the relative data of all the participants are listed and plotted for visualization. There are two sets of the relative data: the first set is based on the submitted measurement data without any correction. The second set is based on the data corrected to one junction voltage as a result of the temperature correction. By comparison of the two relative data, one can check if the temperature correction via junction voltage works properly by improving the stability of the artefact LEDs. The scale of all the plot of relative data is fixed (from 0.96 to 1.04) for a better comparison. Note that the non-correlated uncertainty of the pilot lab is smaller than 0.7 % (k = 1) for all the type of LEDs.

2. MIKES (SET #1)

2.1. WITHOUT CORRECTION

r1 r2

R-1 1.0001 0.9939

R-2 1.0093 0.9991

R-3 1.0033 0.9943

G-1 1.0014 1.0045

G-2 0.9999 1.0037

G-3 0.9968 0.9938

B-1 0.9981 1.0095

B-2 0.9893 0.9994

B-3 1.0007 1.0030

W-1 1.0541 0.9853

W-2 0.9886 0.9938

W-3 0.9879 0.9902

D-1 1.0007 1.0051

D-2 0.9958 0.9983

2.2. WITH TEMPERATURE CORRECTION

r1_cor r2_cor

R-1 0.9981 0.9976

R-2 1.0035 1.0024

R-3 1.0003 0.9981

G-1 0.9999 1.0050

G-2 0.9999 1.0054

G-3 0.9953 0.9946

B-1 0.9999 1.0111

B-2 0.9904 1.0004

B-3 0.9976 1.0006

W-1 1.0525 0.9849

W-2 0.9885 0.9945

W-3 0.9883 0.9912

D-1 1.0008 1.0054

D-2 0.9953 0.9985

3. CMS-ITRI (SET #2)


r1 r2

R-1 1.0116 0.9988

R-2 1.0029 0.9920

R-3 1.0015 0.9932

G-1 1.0390 0.9879

G-2 0.9972 0.9977

G-3 0.9920 0.9862

B-1 0.9885 1.0028

B-2 0.9990 1.0079

B-3 0.9984 1.0033

W-1 1.0073 0.9967

W-2 1.0000 0.9981

W-3 0.9997 0.9982

D-1 0.9971 0.9999

D-2 0.9982 1.0048


r1_cor r2_cor

R-1 1.0001 1.0077

R-2 0.9929 1.0031

R-3 0.9912 1.0050

G-1 1.0384 0.9908

G-2 0.9960 0.9999

G-3 0.9883 0.9866

B-1 0.9892 1.0040

B-2 0.9952 1.0068

B-3 0.9998 1.0051

W-1 1.0058 0.9997

W-2 0.9984 1.0012

W-3 0.9946 1.0002

D-1 0.9974 0.9999

D-2 0.9981 1.0046

4. PTB (SET #3)


r1 r2

R-1 0.9940 1.0183

R-2 0.9762 1.0024

R-3 0.9908 1.0182

G-1 0.9933 1.0074

G-2 0.9976 1.0031

G-3 0.9934 1.0053

B-1 0.9987 1.0051

B-2 0.9754 0.9925

B-3 1.0089 1.0195

W-1 0.9883 1.0060

W-2 0.9905 1.0091

W-3 0.9955 1.0107

D-1 0.9922 1.0023

D-2 0.9985 1.0070


r1_cor r2_cor

R-1 0.9996 1.0102

R-2 0.9865 0.9954

R-3 0.9985 1.0097

G-1 0.9972 1.0057

G-2 0.9997 1.0006

G-3 0.9954 1.0014

B-1 0.9992 1.0060

B-2 0.9752 0.9925

B-3 1.0086 1.0185

W-1 0.9941 1.0012

W-2 0.9956 1.0041

W-3 0.9995 1.0055

D-1 0.9946 0.9993

D-2 1.0013 1.0048

5. NMIJ (SET #4)


r1 r2

R-1 0.9873 1.0019

R-2 0.9958 1.0081

R-3 0.9977 1.0093

G-1 0.9976 1.0099

G-2 0.9947 1.0044

G-3 0.9913 1.0021

B-1 0.9689 0.9844

B-2 1.0020 1.0142

B-3 1.0074 1.0230

W-1 0.9856 1.0113

W-2 0.9892 1.0082

W-3 0.9942 1.0115

D-1 0.9957 1.0044

D-2 0.9956 1.0043


r1_cor r2_cor

R-1 0.9947 1.0005

R-2 0.9976 1.0021

R-3 1.0003 1.0048

G-1 0.9990 1.0088

G-2 0.9959 1.0029

G-3 0.9929 1.0006

B-1 0.9688 0.9845

B-2 1.0019 1.0144

B-3 1.0071 1.0233

W-1 0.9907 1.0092

W-2 0.9906 1.0049

W-3 0.9957 1.0089

D-1 0.9983 1.0027

D-2 0.9969 1.0021

6. CENAM (SET #5)


r1 r2

R-1 0.9920 0.9866

R-2 1.0017 1.0010

R-3 1.0134 1.0053

G-1 0.9898 0.9791

G-2 0.9975 1.0020

G-3 1.0183 1.0133

B-1 1.0293 1.0152

B-2 0.9990 0.9827

B-3 0.9902 0.9836

W-1 0.9962 0.9990

W-2 1.0019 1.0002

W-3 1.0022 1.0005

D-1 1.0033 1.0031

D-2 0.9972 0.9964


r1_cor r2_cor

R-1 0.9917 0.9863

R-2 1.0011 1.0004

R-3 1.0134 1.0070

G-1 0.9905 0.9799

G-2 0.9968 1.0020

G-3 1.0174 1.0133

B-1 1.0301 1.0159

B-2 0.9983 0.9822

B-3 0.9900 0.9835

W-1 0.9985 0.9976

W-2 1.0030 0.9988

W-3 1.0026 0.9995

D-1 1.0016 1.0053

D-2 0.9948 0.9983

7. LNE (SET #6)


r1 r2

R-1 1.0098 0.9906

R-2 1.0005 0.9897

R-3 1.0133 0.9961

G-1 1.0042 0.9979

G-2 1.0039 0.9957

G-3 0.9998 0.9986

B-1 1.0096 1.0046

B-2 1.0004 0.9972

B-3 0.9936 0.9946

W-1 0.9861 1.0146

W-2 0.9915 1.0091

W-3 0.9941 1.0047

D-1 1.0002 0.9985

D-2 1.0012 1.0000


r1_cor r2_cor

R-1 1.0058 0.9950

R-2 0.9964 0.9946

R-3 1.0082 0.9999

G-1 1.0020 0.9986

G-2 1.0032 0.9978

G-3 0.9980 1.0004

B-1 1.0090 1.0047

B-2 0.9998 0.9976

B-3 0.9935 0.9954

W-1 0.9852 1.0171

W-2 0.9884 1.0102

W-3 0.9921 1.0070

D-1 0.9977 0.9999

D-2 1.0001 1.0023

8. METAS (SET #7)


r1 r2

R-1 1.0024 0.9959

R-2 1.0052 1.0014

R-3 1.0001 0.9951

G-1 1.0018 0.9971

G-2 1.0000 0.9985

G-3 1.0031 0.9995

B-1 0.9988 1.0006

B-2 1.0104 1.0076

B-3 0.9957 0.9869

W-1 1.0024 1.0041

W-2 0.9979 0.9983

W-3 0.9992 0.9981

D-1 0.9999 1.0024

D-2 0.9942 1.0036


r1_cor r2_cor

R-1 1.0035 0.9944

R-2 1.0086 1.0029

R-3 0.9981 0.9924

G-1 1.0019 0.9967

G-2 1.0008 0.9986

G-3 1.0033 0.9986

B-1 0.9988 1.0007

B-2 1.0132 1.0105

B-3 0.9930 0.9839

W-1 1.0019 1.0031

W-2 0.9990 0.9976

W-3 1.0010 0.9974

D-1 1.0018 1.0023

D-2 0.9944 1.0015

9. A*STAR (SET #8)


r1 r2

R-1 1.0025 1.0019

R-2 0.9966 1.0002

R-3 0.9997 0.9991

G-1 1.0030 1.0011

G-2 1.0004 1.0025

G-3 0.9947 0.9984

B-1 0.9958 0.9966

B-2 1.0039 0.9994

B-3 1.0024 1.0018

W-1 1.0004 1.0031

W-2 0.9965 1.0018

W-3 0.9967 1.0014

D-1 0.9953 0.9995

D-2 1.0021 1.0031


r1_cor r2_cor

R-1 1.0028 0.9994

R-2 0.9978 0.9990

R-3 1.0018 0.9991

G-1 1.0037 1.0008

G-2 1.0004 1.0014

G-3 0.9957 0.9979

B-1 0.9959 0.9964

B-2 1.0041 0.9993

B-3 1.0024 1.0018

W-1 1.0010 1.0012

W-2 0.9978 1.0004

W-3 0.9988 1.0007

D-1 0.9961 0.9989

D-2 1.0024 1.0026

10. VSL (SET #1)


r1 r2

R-1 1.0046 1.0051

R-2 0.9931 0.9968

R-3 1.0008 0.9995

G-1 0.9989 0.9941

G-2 1.0046 1.0025

G-3 0.9959 1.0040

B-1 1.0033 1.0010

B-2 0.9924 1.0061

B-3 0.9975 0.9996

W-1 0.9913 0.9986

W-2 0.9940 1.0099

W-3 0.9938 1.0125

D-1 1.0034 1.0113

D-2 0.9914 0.9939


r1_cor r2_cor

R-1 1.0065 1.0036

R-2 0.9962 0.9927

R-3 1.0041 0.9969

G-1 1.0004 0.9931

G-2 1.0057 1.0008

G-3 0.9974 1.0027

B-1 1.0034 1.0016

B-2 0.9923 1.0061

B-3 0.9978 0.9988

W-1 0.9946 0.9973

W-2 0.9966 1.0069

W-3 0.9960 1.0086

D-1 1.0072 1.0135

D-2 0.9890 0.9902

11. NIST (SET #3)


r1 r2

R-1 1.0054 0.9992

R-2 0.9939 0.9926

R-3 1.0067 1.0023

G-1 1.0099 1.0091

G-2 0.9924 0.9953

G-3 0.9974 0.9959

B-1 0.9891 0.9956

B-2 1.0011 1.0014

B-3 1.0033 1.0095

W-1 0.9995 1.0017

W-2 0.9975 1.0026

W-3 0.9979 1.0009

D-1 0.9992 1.0055

D-2 0.9951 1.0002


r1_cor r2_cor

R-1 1.0061 0.9959

R-2 0.9952 0.9907

R-3 1.0097 1.0024

G-1 1.0107 1.0088

G-2 0.9922 0.9938

G-3 0.9988 0.9958

B-1 0.9889 0.9953

B-2 1.0009 1.0012

B-3 1.0039 1.0098

W-1 1.0002 1.0021

W-2 0.9977 1.0029

W-3 0.9976 0.9995

D-1 0.9997 1.0059

D-2 0.9948 0.9997

12. VNIIOFI (SET #5)


r1 r2

R-1 1.0017 1.0032

R-2 1.0008 0.9987

R-3 0.9986 0.9969

G-1 1.0065 1.0195

G-2 0.9724 0.9873

G-3 1.0093 1.0051

B-1 0.9895 0.9967

B-2 1.0202 1.0241

B-3 0.9815 0.9880

W-1 0.9990 1.0057

W-2 0.9942 1.0004

W-3 0.9990 1.0017

D-1 0.9904 1.0030

D-2 0.9997 1.0069


r1_cor r2_cor

R-1 1.0013 1.0036

R-2 0.9989 0.9988

R-3 0.9993 0.9982

G-1 1.0057 1.0192

G-2 0.9720 0.9875

G-3 1.0096 1.0059

B-1 0.9903 0.9976

B-2 1.0195 1.0232

B-3 0.9815 0.9879

W-1 1.0002 1.0048

W-2 0.9953 0.9988

W-3 0.9986 1.0024

D-1 0.9902 1.0034

D-2 0.9997 1.0068

13. MKEH (SET #6)


r1 r2

R-1 0.9983 1.0023

R-2 0.9994 *

R-3 * *

G-1 0.9295 *

G-2 * *

G-3 1.0313 1.0392

B-1 0.9948 1.0058

B-2 1.0043 1.0154

B-3 0.9797 *

W-1 0.9976 1.0013

W-2 0.9969 1.0055

W-3 0.9945 1.0041

D-1 1.0005 1.0046

D-2 0.9949 *

* damaged


r1_cor r2_cor

R-1 0.9998 1.0019

R-2 0.9984 *

R-3 * *

G-1 0.9291 *

G-2 * *

G-3 1.0322 1.0387

B-1 0.9946 1.0054

B-2 1.0049 1.0159

B-3 0.9793 *

W-1 0.9978 1.0014

W-2 0.9971 1.0051

W-3 0.9951 1.0034

D-1 1.0005 1.0051

D-2 0.9944 *

* damaged

14. INM (SET #7)


r1 r2

R-1 0.9844 1.0133

R-2 0.9764 0.9974

R-3 1.0057 1.0229

G-1 1.0008 1.0166

G-2 0.9863 0.9955

G-3 0.9929 1.0079

B-1 0.9727 1.0199

B-2 0.9896 1.0141

B-3 0.9866 1.0171

W-1 0.9898 1.0059

W-2 0.9964 1.0089

W-3 0.9919 1.0070

D-1 0.9999 1.0062

D-2 0.9936 1.0004


r1_cor r2_cor

R-1 0.9894 1.0107

R-2 0.9843 0.9965

R-3 1.0050 1.0140

G-1 1.0022 1.0143

G-2 0.9887 0.9943

G-3 0.9947 1.0058

B-1 0.9734 1.0204

B-2 0.9904 1.0147

B-3 0.9861 1.0150

W-1 0.9958 1.0006

W-2 1.0009 1.0051

W-3 0.9954 1.0022

D-1 1.0184 1.0224

D-2 0.9774 0.9819

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