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11 Copyright (c) Lumileds Lighting LLC Company ConfidentialCopyright (c) Lumileds Lighting LLC Company Confidential

LED CharacteristicsLED CharacteristicsErik Swennen & Patrick van der MeulenErik Swennen & Patrick van der Meulen

22Copyright (c) Lumileds Lighting LLC Copyright (c) Lumileds Lighting LLC

Lumileds ConfidentialLumileds Confidential

LED Characteristics

•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision

•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision

•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT

•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning

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LED Characteristics







Φ

Flux (units: lumen, watts)

The The amountamount of of light radiatedlight radiatedbyby a a light sourcelight source..

Unit: Unit: lumenlumen (lm (lm -- photometricphotometric))Watts (W Watts (W -- radiometricradiometric))

3



Luminous Flux Measurement

Baffle

• LumiLeds test method• Test method measures total luminous flux emitted into a defined

acceptance angle

Device under test Defined acceptance angle

Photometrically weightedoptical detector

Φv ≈ Electrical signalarea spherearea detectorSphere with highly

reflective whitediffuse coating oninside surface

θ



�

Intensity (unit: candela (lm/sr), W/sr)

The The amountamount of of light radiatedlight radiatedbyby a a light sourcelight source in a in a given directiongiven direction..

1 1 candelacandela = 1 = 1 lumenlumen per per steradiansteradian

�

4



Luminous Intensity Measurement

Device under test

• Test method only accounts for luminous flux in a small portion of optical beam

Iv ≈ Electrical signal d2

Area detector

ω≈ Area detectord2d

Photometrically weightedoptical detector

ω



LED Characteristics





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Radiometry & Photometry

•• Radiometric light is specified according to its Radiometric light is specified according to its radiant energy and power without regard for the radiant energy and power without regard for the visual effects of radiation. Prefix: visual effects of radiation. Prefix: RadiantRadiant or or RadiometricRadiometric

•• Photometric light is specified as radiation in Photometric light is specified as radiation in terms of human visible response according to the terms of human visible response according to the CIE standard observer response curve (photopic CIE standard observer response curve (photopic luminous efficiency function). Prefix: luminous efficiency function). Prefix: LuminousLuminous



wavelength (nm) →

rela

tive

eye

sens

itivi

ty →

4000

500 600 700 800

V(λ)

555 nm0,2

0,4

0,6

0,8

1,0

1 W555nm = 683 lm

Eye Sensitivity

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From Watts to Lumens

WavelengthWavelength LuminousLuminous ConversionConversionEfficiencyEfficiency Factor [lm/W]Factor [lm/W]

400 400 0.004 0.004 0.30.3450 450 0.040.04 2626500 500 0.3 0.3 221221555 555 1.0 1.0 683683600 600 0.63 0.63 431431650 650 0.11 0.11 7373700 700 0.0040.004 2.82.8



Basics of human vision•• Light projected on the retina by Light projected on the retina by

the lensthe lens•• Retina contains light sensitive Retina contains light sensitive

cells cells –– rods & conesrods & cones•• Rods are more sensitive, no Rods are more sensitive, no

color difference (scotopic vision)color difference (scotopic vision)•• Cones have color sensitive Cones have color sensitive

pigments pigments –– red, green & blue red, green & blue (photopic vision)(photopic vision)

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LED Characteristics







Colorimetry•• Basic quantity for colorimetry is the spectrum S(Basic quantity for colorimetry is the spectrum S(λλ))•• ‘standard observer’ CIE 1931 :color matching functions‘standard observer’ CIE 1931 :color matching functions

X, Y and Z are called the tristimulus valuesX, Y and Z are called the tristimulus values•• Y represents brightness (nit, lumen, ... )Y represents brightness (nit, lumen, ... )•• Many different spectra can yield the sameMany different spectra can yield the same

color for the human eye (metamerism) color for the human eye (metamerism) ⇒there is no way back from XYZ to spectrumthere is no way back from XYZ to spectrum

300 400 500 600 700 8000

0.5

1

1.5

2x-ba ry-ba rz -ba r

λd).λ(x).λ(S.683X780

380∫=

λd).λ(y).λ(S.683Y780

380∫=

λd).λ(z).λ(S.683Z780

380∫=

400 500 600 700 8000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

wa ve le ngth (nm )

colo

r mat

chin

g va

lue

CIE x-ba rCIE y-ba rCIE z -ba r

300 400 500 600 700 8000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

wavelength (nm)

colo

r mat

chin

g va

lue

CIE x-barCIE y-barCIE z-bar

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Colorimetry

xyxy--diagram CIE1931diagram CIE1931

ZYXXx++

=ZYX

Yy++

=3y12x2

x4'u++−

=3y12x2

y9'v++−

=

u’v’u’v’--diagram CIE1976diagram CIE1976



Peak or Dominant Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

x coordinates

480

460

500

520

540

560

580

600

620640

Dominant Wavelength

CIE Illuminant E

(x, y) Coordinate

ab

baPurityColor =

0.00.10.20.30.40.50.60.70.80.91.0

400 450 500 550 600 650 700Wavelength (nm)

Rel

ativ

e In

tens

ity

RED

AMBERROYAL BLUE

BLUE

CYAN

GREEN

Color purity = a / b

Dominant wavelength (Illuminant E)

Peakwavelength = highest radiometric energy

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Visual perception of white light

The color impression of light is characterized by:

• Color temperature (Tc)• Color rendition (Ri) • Reflection properties of material being illuminated



Blackbody radiators

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Color Coordinates of Blackbody (Planckian) Radiators

x coordinates

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

y co

ordi

nate

s

480

460

500

520

540

560

600

620640Blue Dwarf

Star20K-50K

CIE Illuminant E

NTSC White6500K

Cool-whiteFluorescent5400K

12V Halogen Bulb 3000K

Household Incandescent 2800K

12V Instrument Cluster Bulb 2500K

Warm-whiteFluorescent 3000K

M.P. Iron1810K

M.P. Tungsten3700K

M.P. Copper 1360K

"Red-hot" Poker (1000K = 1340F)

580

Tc = 5500K

Tc = 2200K



Color Temperature in CIE1931 Diagram

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

x coordinates

480

460

500

520

540

560

580

600

620640

50,000K20,000K

10,000K

8000K 6667K5714K

5000K

∞

4444K 4000K

3636K

3333K3077K

2857K2500K

1667K2000K

Planckian Locus

CIE Illuminant E

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Color Rendering Index

Sunlight Has a CRI of 100. When objects are illuminated with sunlight, all the colors look good.

Low Pressure Sodium has a CRI less than 0. Objects illuminated by it all look brown.



Color Rendering CalculationLight Grayish Red Light Bluish Green

Dark Grayish Yellow Light Blue

Strong Yellow Green Light Violet

Moderate Yellowish Green

Light Reddish Purple

400 500 600700

400 500 600700400 500 600700

400 500 600700

400 500 600700 400 500 600700

400 500 600700 400 500 600700

Wavelength [nm]

• Spectra of 8 definedsamples are combined withthe spectrum of the source(e.g. White LED)

•The shift of the color point of every sample is calculated:

R1 to R8

•The average Ra shift is then calculated:

•Ra = 1/8 (R1 + R2 +...+ R8)

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Color Rendering Index (Ra)

•• RRaa = 90 = 90 -- 100100Excellent Excellent colorcolor rendering propertiesrendering properties

•• RRaa = 80 = 80 -- 9090Good Good colorcolor rendering propertiesrendering properties

•• RRaa = 60 = 60 -- 8080Moderate Moderate colorcolor rendering propertiesrendering properties

•• RRaa < 60< 60Poor Poor colorcolor rendering propertiesrendering properties



LED Characteristics





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Working Principle of an LED

•Same principle for all colors

(AlInGaP & InGaN)

•Power dissipation:1-5 Watt

•Package Extraction Efficiency: >95%

•Maximum Ratings

•Tjunction-max = 120 °C / 135°C

• Iforward-max = Product dependent

Iforward

(Electrons)

Vforward

φvisible (Photons)

PN-Junction

Electrical Model

Anode

Cathode



InGaN vs AlInGaP LED Technology

Anode

Cathode

Blue3.4 V at 350 mA

7 V at -100 uA

Anode

Cathode

Red/Amber3.0 V at 350 mA

20V at -100 mA

InGaN AlInGaP

GaP Substrate( ~ 200 µm)

AuZn Contact Pad

n-Al0.5In0.5P (LCL)

(AlxGa1-x)0.5In0.5PActive Layer

VPE GaP Window( ~ 50 µm)

p-Al0.5In0.5P (UCL)

LED JunctionSilver reflector

InGaNSapphire

Light

Wire bond Silicon submount

LED Junction

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Luxeon Slug Electrical PotentialLuxeon Slug Electrical Potential

SlugAlInGaP Die in 1WBatwing Package

SlugInGaN Die in all

Luxeon Packages

LED Chip

Cathode LeadAnode Lead

BodyPlastic Lens

Slug

slug

SlugAlInGaP Die in 1W Lambertian & SideEmitter Package

+

-+

-

-

+

+

-

+ OR -



LED Characteristics





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Light Output Characteristics•• Flux with CurrentFlux with Current•• TTjunctionjunction = 25= 25ooCC



Light Output vs Junction Temp

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Forward Current Characteristics



Wavelength Characteristics

0.00.10.20.30.40.50.60.70.80.91.0

400 450 500 550 600 650 700Wavelength (nm)

Rela

tive

Inte

nsity

RED

AMBERROYAL BLUE

BLUE

CYAN

GREEN

Dominant Wavelength:

RED=629nm GREEN=530nm

AMBER=590nm CYAN=505nm

BLUE=470nm

ROYAL BLUE=455nm

Spectral Halfwidth:

RED=19nm GREEN=35nm

AMBER=19nm CYAN=30nm

BLUE=25nm

ROYAL BLUE=20nm

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LED Characteristics







Luxeon Binning Example: Green

Batch to Batch

Variations

Num

ber o

f Par

ts P

rodu

ced

M

13.9

N

18.1

O

23.5 30.6

1.31.3

Flux bins

Bin Limits [lm]

Ratio Upper/Lower 1.3

L P

Num

ber o

f Par

ts P

rodu

ced

G

2.79

H

3.03

J

3.27 3.51

0.240.24

Voltage bins

Bin Limits [V]

Bin Width [V] 0.24

Batch to Batch

Variations

F K

Num

ber o

f Par

ts P

rodu

ced

2

525

3

530

4

535 540

5.05.0

Color bins

Bin Limits[nm]

Bin Width [nm] 5.0

Batch to Batch

Variations

1 5 6

Bining

=

Subdividing large quantities

into manageable quantities

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Luxeon Binning

•• Lumileds LEDs are 100% electrically and optically testedLumileds LEDs are 100% electrically and optically tested

•• Each unit is binned for Each unit is binned for •• Luminous Flux, Luminous Flux, •• Forward Voltage Forward Voltage •• Dominant Wavelength or Correlated Color TemperatureDominant Wavelength or Correlated Color Temperature

• All binning is done at • nominal current• Junction Temperature of 25°C (Flash mode)



LED Parameter vs.Temperature

0

1

2

570 580 590 600 610 620 630

Wavelength [nm]

Rel

ativ

e In

tens

ity

+25°C

+85°C

λpeak

Tamb = -20°C

As temperature rises:

• Light Output decreases

• Wavelength gets longer (towards red), except for White

• Forward Voltage decreases

0

50

100

150

200

250

300

350

400

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Forward Voltage (V)

Forw

ard

Cur

rent

(mA

)

Red, Reddish Orange,

Amber(AlInGaP)

Royal Blue, Blue, Cyan,

Green, White (InGaN)

∆Vf ≈ -2mV / °C

Amber

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Dominant λ vs. Temperature

As LED’s get hotter, colors shift to longer wavelengths.NOTE: This number is different for λpeak

Example: What is the color shift of an amber LED whose Tj is 40°C? What will λD be at Tj 40 °C?

λD1 = 590 nm (@T1= 25 °C)λD2 = ? nm (@T2= 40 °C)

∆ λD (λD2-λD1) ∆ T (T2-T1)

∆ λD = (.09 nm/ °C)* (T2-T1) = (.09 nm/ °C)*(40 -25 °C) = 1.35 nm

Therefore, λD2 = 591.35 nm

)( Cnm/TλD °∆∆

≈ K

Color K (nm/ºC)Amber .09

Red .03

Blue .04

Green .04

Cyan .04

=

= .09 nm/ °C

3838 Copyright (c) Lumileds Lighting LLC Company ConfidentialCopyright (c) Lumileds Lighting LLC Company Confidential

LED CharacteristicsLED CharacteristicsErik Swennen & Patrick van der MeulenErik Swennen & Patrick van der Meulen

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