Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a...

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1 Measurement of LEDs and Solid State Lighting Yoshi Ohno (Director, CIE Div.2) Optical Technology Division National Institute of Standards and Technology Gaithersburg, Maryland USA CIE/USA-Canada Joint Technical Session, October 18, 2007

Transcript of Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a...

Page 1: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Measurement of LEDs andSolid State Lighting

Yoshi Ohno(Director, CIE Div.2)

Optical Technology DivisionNational Institute of Standards and Technology

Gaithersburg, Maryland USA

CIE/USA-Canada Joint Technical Session, October 18, 2007

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Outline

1. SSL products - commercialization support

2. Measurement standards for LED/SSL products

3. NIST facilities for LED/SSL measurements

4. Research on Color Quality of LED/SSL sources

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Solid State Lighting – Driving Force

Lighting consumes 22 % of electricity 8 % of total energy (statistics of USA)

Solid State Lighting, by 202550% reduction of energy consumed by lighting10% reduction in greenhouse gas emissionsCustomer savings of $30 billion annually(U.S. Dep. Energy)

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1840 1890 1940 1990 2040

Year

Lum

inou

s Ef

ficac

y (lm

/W)

Fire

Incandescent

Fluorescent, HIDSolid-State Lighting

Oil

KeroseneGas Mantle

Carbon Filament

Tungsten Filament

History of Light Sources

IEEE Circuits and Devices Vol 20, No 3, pp 28-37, May/June, 2004

1850 1900 1950 2000

1000

100

10

1

0.1

0.01

Theoretical limit

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Luminous Efficacy – Goal of SSL

Ref. IESNA Lighting Handbook, Ninth Edition, p. 26-3 (2000).

White LEDs (2007)Products Prototypes

200 lm/W(products)

Goal in 2025

130 lm/W

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LuminousEfficacyof a Source[lm/W]

=LuminousEfficacy ofRadiation[lm/W]

Luminous flux [lm] Optical power [W]

Luminous flux [lm]Electrical power [W]

(Theoreticalmaximum lm/W)

RadiantefficiencyX

Optical power [W]Electrical power [W]

(External Q.E.)(“Wall-plug efficiency”)

Rationale for 200 lm/W

Goal: 200 lm/W 400 lm/W 50 %

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0

100

200

300

400

500

600

700

800

400 450 500 550 600 650 700 750Wavelength (nm)

1.0

0.5

0

Km = 683

V(λ)

Luminous Efficacy of Radiation

<Examples of LER>Tri-p FL (3300 K) ~350 lm/WCW FL (4300 K) ~340 lm/WMH (4300 K) ~300 lm/W

555 nm

!

K =Km S(")V (")d"

"#

S(")d""#

[lm/W]

( Km = 683 lm/W)

S(λ)

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RGB(Y) white LED Simulation

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Source: Mike Krames (Lumileds)

External Quantum Efficiency of LEDs

White LED efficacy 200 lm/W

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SSL products are coming out

Niche applications

General lighting applications

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DOE’s SSL Commercialization Support

http://www.netl.doe.gov/ssl/materials_2007.html

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DOE Energy Star program for SSL products

• SSL products for general illumination(residential and commercial applications)

• Category A (niche applications),Category B (general lighting)

• Requirements for luminaire efficacy,chromaticity, and CRI (Ra >75 for indoorapplications).

• Ensure quality as well as energy efficiency

• Requires standards for test methods.

• Requires laboratory accreditation.

20Outdoor step lights

70Category B

25Outdoor pathwaylights

24Outdoor porch lights

35Recessed downlights

29Portable desk/Task

24Under cabinet kitchen

Min. lm/W

http://www.netl.doe.gov/ssl/energy_star.html

Final version 9/12/2007

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DOE SSL Commercial Product Testing Program(CALiPER - formerly, CPTP)

Workshop held Oct. 27, 2006 http://www.netl.doe.gov/ssl/workshopHighlights-CPTP.htm

Objective:- Provide high quality performance information, discourage low

quality products.- Support R & D planning- Support ENERGY STAR- Inform industry test procedures and standards

Key actors:- DOE, PNNL- Independent testing labs

• Tests may includetotal luminous flux, luminousEfficacy, color characteristicsstability, life testing, and more.

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Provide calibration services for LED and SSL products. Research on color quality.

NIST is funded by DOE for

Developing NVLAP program for SSL - Handbook 150-A, Round-robin proficiency testing.

Measurement support- verification of measurements in CALiPER program- test of prototypes from DOE projects

Standards development- ANSI C78.377 chromaticity of SSL products- IESNA LM-79 photometric measurement of SSL products- CIE standard on color rendering (TC1-69)

- participating in other standards development

NIST Role

NIST leads

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1. SSL products - commercialization support

2. Measurement standards for LED/SSL products

3. NIST facilities for LED/SSL measurements

4. Research on Color Quality of LED/SSL sources

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Measurement of LED/ SSL Products

LED modules / clusters

SSL products

Total luminous flux (lm) Luminous efficacy

(lm/W) Luminous intensity (CIE

Averaged Intensity) Chromaticity, CCT, Duv,

CRI Angular intensity

distribution Luminaire efficacy

(lm/W)

Measurement quantitiesLED chips / packages

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LED chips / packages

LED modules / clusters

SSL products

Standards for measurement of LED/ SSL products

CIE 127:2007

IESNA LM-79 Photometric Meas. (draft)IESNA LM-80 Life time (draft)ANSI C78.377 Chromaticity (draft)

does not address issues onhigh power LEDs

No standards / recommendationCIE TC2-50

CIE TC2-46, TC2-58CIE R2-36

No CIE publications, no TCs

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CIE 127:2007 Measurement of LED (2nd ed.)

Major changes from last version (1997)

New section on total luminous fluxmeasurement.- Improved sphere geometries recommended- Partial LED flux defined.

New section on spectral measurement (forcolorimetric as well as photometric quantities)- Input geometries (irradiance mode, total flux

mode, partial flux mode)- New recommendation on bandwidth and

scanning interval (5 nm, for color)

50 mm diam.

d

x!

"LED,x

Still does not address high power LEDs.

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A big issue in High Power LED measurement

LEDs in SSL products are operating at much highertemperature. lm/W drops to 1/2 (in some cases) in luminaires.

Large gap between published LED chip performance (lm/W)and SSL products performance (lm/W).

A standard for high power LED specifications under realisticconditions (as used in luminaires) is urgently needed.

<LED data example>

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Approach at NIST

Measure high power LEDs at a fullDC current at thermal equilibrium.

(A heat sink is needed; results varydepending on size of heat sink, ambienttemp. and how LED is mounted)

Use a temperature-controlled heatsink. Set heat sink temperature at50°C, 60°C, ….(need to be standardized)

Use a metal-core PC board tomount the LED to the heat sink.

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Data example

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Measurement of SSL products

Luminaires are measured for relative luminous intensitydistribution and total luminous flux, normalized bymeasured lamp total luminous fux, e.g., per 1000 lm.

Absolute scale is given by published lamp lumen values.

Traditional luminaire photometry (Relative Photometry)

This method does not work for SSL products.

• Lamp and fixture cannot be separated.• Published LED luminous flux values

are not reliable.

SSL products: mostly in a form of luminaire

Existing standards do not fulfill the needs for SSL.

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IESNA LM-79 Approved Method for Electrical andPhotometric Measurement of SSL Products (Draft)

Covers SSL products complete with electronics andheat sinks. --- therefore, no temperature issues (SSLproduct operated at 25°C ambient).

Does not cover LED modules, LED packages, norindividual LEDs.

Addresses both aspects of lamp photometry andluminaire photometry

• Total luminous flux (lumen), electrical input,luminous efficacy (lm/W)

• Chromaticity, CCT, CRI (4 π integrated)• Goniophotometry (angular intensity distribution)

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Total luminous flux and color quantities measured at the same time. No spectral mismatch correction needed for luminous flux. Color quantities measured as spatially (4π) averaged values. Total spectral radiant flux standards available from NIST.

!

Total spectra

radiant flux

"

# $

%

& '

One of the methods recommended (for small SSL products)

A goniphotometer is needed for large-size SSL products)

IESNA LM-79

l

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Chromaticity issues

Not acceptableNot preferred

Neodymium

CCT and CRI do not tell the whole story.

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ANSI C78.377 Specifications for the Chromaticity ofSSL products (Draft)

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Flexible Color

2) T is chosen to be at 100 K steps (2800, 2900, …., 6400 K), excluding those eight nominal

CCTs listed in Table 1.

3) T is given by

!

"T = 0.0000108#T2

+ 0.0262#T + 8 .

4) Duv is given by

!

Duv = 57700# (1/T )2$ 44.6# (1/ T )+ 0.0085.

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1. SSL products - commercialization support

2. Standardization for LED/SSL products

3. NIST facilities for LED/SSL measurements

4. Research on Color Quality of LED/SSL sources

Page 29: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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!

"# ,ref (#) = A $E# (#)

External reference flux:

!

"# ,test (#) =ytest (#)

yref (#)$ kcor(#) $"# ,ref (#)

Spectral radiant flux of thetest lamp:

kcorr(λ): correction factor

* Absolute scale of radiantflux is based on the NISTlumen.

NIST Facilities for LED/SSL measurements

2.5 m absolute integrating sphere

Page 30: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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2.5 m absolute integrating sphere

Measuring a refrigerator LEDluminaire

• Total luminous flux (lm)• Total spectral radiant flux (350 nm to 830 nm)• Chromaticity, CCT, Duv, CRI

(4 π averaged)• 25°C ambient temp.• SSL products up to ~30 cm

diameter or linear ~1.5 mlong.

• Individual LEDsalso measured.

For SSL products

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Data example (LED down light)

2.5 m absolute integrating sphere

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Encoder

Steppingmotor

Lighttrap

Servomotor

Servomotor

Laser

Fiberbundle

Irradiancehead

Spectro-radiometer

Rotationcoupling

1.2

5 m

!

"

• Total spectral radiant flux scale• Measurement of small SSL products - Angular luminous intensity distribution - Color uniformity

Gonio-spectroradiometer

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Luminous intensity distribution Color uniformity[cd]

Data example (LED down light)

Gonio-spectroradiometer

Page 34: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Goniophotometerfor luminousintensity distribution

Reference spectroradiometer(double-monochromator) for LEDcolor measurement

Variable temperature chamber (~10°C to 35°C)

Other NIST instruments for LEDs

Page 35: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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NIST Calibration Services for LED/SSL Products

Photometric and radiometric quantities Total luminous flux (lm), luminous efficacy (lm/W) Total radiant flux (W) … (350 - 830 nm) Luminous Intensity CIE Averaged LED Intensity A/B Luminous intensity distribution (small sources)

Color quantities Chromaticity coordinates (x,y), (u’, v’) Correlated color temperature Color Rendering Index (CRI Ra) Dominant wavelength λd Spectral distribution (total spectral radiant flux)

Page 36: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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1. SSL products - commercialization support

2. Standardization for LED/SSL products

3. NIST facilities for LED/SSL measurements

4. Research on Color Quality of LED/SSL sources (update)

Page 37: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Daylight Low pressuresodium lampWhite LED

520 lm/W~ 400 lm/W~ 250 lm/WTheoretical maximum

Color Quality vs. Energy Efficiency

Excellent color rendering

??color rendering

No colorrendering

Page 38: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Problems of CRI (1)

3-LED Model

Peaks at:457, 540, & 605 nm

CRI Ra =80

Ref.

LED

This spectrum has higher lm/W.

Good scores do not guarantee good saturated colors

Page 39: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Problems of CRI (2)

CRI penalizes light sources having enhanced color contrast.

Neodymium incandescentlamp

CRI Ra = 77(Normal incandescent lampRa =100)

Ref.

LED

Page 40: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Problems of CRI (2)

Products are optimized for metric.Outdated metric impedes development of new technologies.

RGB white light can have the same effects

3-LED ModelPeaks at:464, 538, 620 nm

CRI Ra = 63

Ref.

LED

Page 41: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Experimental RGB Source developed at NIST

5000 KRa=93

Broadband5000 KRa = 71

RGB R6205000 KRa = 82

RGB R600

Page 42: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

Viewed under real sourcesBroadband

RGB R620

RGB R600

Page 43: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

Under the sun (5500 K, 88000 lx)

Booth (300 lx)

In the shade (6800 K, 16000 lx)

75

757575

CRI Ra

20Outdoor step lights

70Category B25Outdoor pathway lights

24Outdoor porch lights35Recessed downlights29Portable desk/Task24Under cabinet kitchen

lm/W

SSL Energy Star minimum requirements

Broadband Ra = 93 RGB R620 Ra = 71 RGB R600 Ra = 82

Page 44: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Developing “Color Quality Scale”

■ Fix the problems of CRI (based on color fidelity)1) use 15 saturated reference color samples

2) use the latest color space (CIE LAB)3) use the latest chromatic adaptation formula (CMCCAT2000)4) 0 to 100 scale (CRI can have negative score.)5) CCT factor based on gamut area of ref. Illuminant6) RMS combining of color differences7) Scale normalized for consistency with CRI for fluorescent lamps

■ Address color quality Issue – Saturation factor

Proposed by NIST

Page 45: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Score is decreased for thefull color difference

RefTest

RefTest

Score is not penalized forincrease of chroma.(Score is decreased for hue andlightness shifts)

“Color Quality Scale” Proposed by NIST

Saturation factor

Page 46: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Some Results of CQS

Neodymiuminc. lamp

CRI =77CQS=88

RGB (enhanced)(464/538/620 nm)

CRI =63CQS=80

RGB (poor red)(457/540/605 nm)

CRI =80CQS=74

Cool Whitefluorescent

CRI =63CQS=64

Consistency of scores is maintained for fluorescent lamps

Page 47: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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CIE TC 1-69

CIE TC1-69 Colour Rendition by White Light SourcesEstablished in May 2006

Chair: Wendy Davis (NIST)

TR:To investigate new methods for assessing the colourrendition properties of white-light sources used forillumination, including solid-state light sources, with thegoal of recommending new assessment procedures.

Vision experiments planned by several members.

Page 48: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Spectrally Tunable Lighting Facility

• 48 channels of high- powerLEDs, 400 - 650 nm.

• Spectrally tunable tosimulate white LEDs andtraditional light sources.

• Uniform illumination for thewhole cubicle (500 lx).

• Contract awarded.

• First phase system (16 ch) tobe delivered in May 2008.

Under development at NISTSpecification goal

Page 49: Measurement of LEDs and Solid State Lighting · 2.5 m absolute integrating sphere Measuring a refrigerator LED luminaire •Total luminous flux (lm) •Total spectral radiant flux

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Thank you for your attention.

Contact: [email protected]

Ref. http://physics.nist.gov/OTD (Optical Sensor Group)