Colorimetry of Solid State Light Sources

Colorimetry of Solid Colorimetry of Solid State Light SourcesState Light Sources

J SchandaJ Schanda

University of Pannonia, HungaryUniversity of Pannonia, Hungary

OVERVIEWOVERVIEW Colorimetric descriptorsColorimetric descriptors

CIE CIE colorimetrycolorimetry Advanced colorimetryAdvanced colorimetry

Luminance specificationLuminance specification Brightness of coloured objectsBrightness of coloured objects Brightness/luminance discrepancyBrightness/luminance discrepancy

Updating colorimetric calculationsUpdating colorimetric calculations Application in Application in lightinglighting applications applications

Colour rendering Colour rendering Colour gamut of displaysColour gamut of displays

ColorimetryColorimetry

Colour is a perception Colour is a perception Colorimetry can describe the colour Colorimetry can describe the colour

stimulus in a form correlating to the stimulus in a form correlating to the perceptionperception

Basic colorimetry dewcribes colour Basic colorimetry dewcribes colour matching under specified conditiionsmatching under specified conditiions

Advanced colorimetry seeks correlates Advanced colorimetry seeks correlates to characterise stimuli in dissimilar to characterise stimuli in dissimilar situations according to their situations according to their perceptionsperceptions

CIE colorimetryCIE colorimetry Fundamental Fundamental

eexperiment of xperiment of colour matchingcolour matching Matching the Matching the

test stimulus test stimulus with the additive with the additive mixture of three mixture of three matching stimulimatching stimuli

Matching Matching stimuli:stimuli:R: 700 nm redR: 700 nm redG: 564 nm greenG: 564 nm greenB. 435 nm blueB. 435 nm blue

Matching stimuliMatching stimuli 1 lm Red + 1 lm Red +

4,5907 lm 4,5907 lm Green + Green + 0,0601 lm 0,0601 lm Blue = Blue = equienergetiequienergeticc white white

Colorimetry Colorimetry coupled to coupled to photometry:photometry:

LL = 1.0000 = 1.0000RR + 4.5907 + 4.5907GG + + 0.06010.0601BB

Matching stimuliMatching stimuli To match some To match some

monochromatic monochromatic stimuli one of the stimuli one of the test stimuli had to test stimuli had to be added to the be added to the test stimulus to test stimulus to achieve colour achieve colour match.match.

Linear Linear transformation to transformation to a new set of non-a new set of non-real matching real matching stimuli, called stimuli, called primaries.primaries.

Two sets of colour Two sets of colour matching functions (CMF)matching functions (CMF)

Most sensitive part of Most sensitive part of the retina, the fovea the retina, the fovea covered by a yellow covered by a yellow pigmentation, thus pigmentation, thus central <4°central <4° part of part of fovea has different fovea has different spectral responsivity:spectral responsivity: CIE 1931 CMF = 2° CIE 1931 CMF = 2°

ObserverObserver

CIE 1964 CMF = 10° CIE 1964 CMF = 10° ObserverObserver

10° Observer not 10° Observer not coupled to photometric coupled to photometric observerobserver

( ) ( )y V

The tristimulus valuesThe tristimulus values

The The XX, , YY, , ZZ tristimulus values of a colour tristimulus values of a colour stimulusstimulus 780nm

380nm

780nm

380nm

780nm

380nm

( )d ,

( )d ,

( )d

X k S x

Y k S y

Z k S z

Chromaticity co-ordinates Chromaticity co-ordinates and diagramand diagram, dominant , dominant

wavelengthwavelength

,

,

1

Xx

X Y ZY

yX Y Z

x y z

Dominant wavelength: Dominant wavelength: DD

Excit. purity: Excit. purity: EP ED

DescriptorsDescriptors Coloured Coloured

lights: lights: Dominant Dominant wavelengthwavelength

Near white Near white lights: lights: Correlated Correlated colour colour temperaturtemperature (CCT)e (CCT)

Problems related to the Problems related to the colour matching functions-1colour matching functions-1 CIE 2° system CIE 2° system

based on based on luminance, luminance, i.e. related to i.e. related to the the VV(() ) functionfunction

VV(() function ) function in error in the in error in the blue part of blue part of the spectrumthe spectrum

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w avelength, nm

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V(l) VM(l) y(Stockman-Sharpe-Fach)

Problems related to the Problems related to the colour matching functions-2colour matching functions-2 Enlarged view of Enlarged view of

the 2° photometric the 2° photometric and colorimetric and colorimetric observers, and a observers, and a proposal for a newproposal for a new

CMFCMF Differences for Differences for blueblue

LEDs can be LEDs can be considerableconsiderable

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wavelength, nm

rel.

resp

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sivi

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V(l) VM(l) y(Stockman-Sharpe-Fach)

( )y

Problems related to the Problems related to the colour matching functions-3colour matching functions-3

Three sets Three sets of CMFsof CMFs CIE CIE

2°Observer2°Observer CIE TC 1-36 CIE TC 1-36

recommen-recommen-ded ded functionsfunctions

Vos Vos primariesprimaries

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wavelengths, nm

CM

F

CIE x

CIE y

CIE z

LMS x

LMS y

LMS z

Vos x

Vos y

Vos z

Problems related to the Problems related to the colour matching functions-4colour matching functions-4

CIE colorimetric CIE colorimetric match breaks down match breaks down with LEDs:with LEDs:

Better description Better description

possible using LMS possible using LMS cone fundamentals cone fundamentals derived colour derived colour matching functionsmatching functions

*abΔ 10E

Cone fundamental based Cone fundamental based colour matching functionscolour matching functions

CIE TC 1-36 developed CIE TC 1-36 developed CMF-s and recommendsCMF-s and recommendsa transformation to aa transformation to aCIE 2° similar systemCIE 2° similar system

F

F

F

1.910988 1.394658 0.389317

0.643151 0.395946 0.000000

0.000000 0.000000 1.919339

x l

y m

z s

( ), ( ), ( )l m s

LED chromaticityLED chromaticity

Chromaticity co-Chromaticity co-ordinates of LEDs ordinates of LEDs calculated in the calculated in the standard 2° standard 2° colorimetric colorimetric system (system (xx,,yy) and ) and the cone the cone fundamental fundamental based system based system xxFF,,yyFF

Differences in Differences in second decimal second decimal figurefigure

Name White Blue Green Red

x 0.311 0.150 0.194 0.715

y 0.332 0.030 0.722 0.280

xF 0.315 0.149 0.201 0.712

yF 0.338 0.045 0.734 0.282

Visual and instrumental Visual and instrumental colour matchcolour match

Visual and Visual and instrumental colour instrumental colour matches using matches using standard and cone standard and cone fundamental CMFsfundamental CMFs

a.)

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u'

v'

RGB LEDVisual averageFiltered incandescent

#1

#2

#3

#4

#5

#7

#8#9#6

b.)

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u'

v'

RGB LEDVisual averageFiltered incandescent

#1

#2

#3

#4

#5

#7

#8#9#6

Enlarged view in vicinity of Enlarged view in vicinity of sample #2sample #2

Chromaticity differences at Chromaticity differences at the nine investigated sitesthe nine investigated sites

Advanced colorimetryAdvanced colorimetry

Advanced colorimetry is needed:Advanced colorimetry is needed: Non-equidistantness of Non-equidistantness of x,yx,y diagram diagram Need to describe chromatic adaptationNeed to describe chromatic adaptation Adaptation to different luminance levelsAdaptation to different luminance levels

Chromatic adaptation Chromatic adaptation CIELAB systemCIELAB system CIECAM02 colour appearance modelCIECAM02 colour appearance model Colour rendering, colour preferenceColour rendering, colour preference

Non-equidistancNon-equidistancttnessness

Mac Mac Adam Adam ellipseellipsess

Chromatic adaptationChromatic adaptation

CIELAB systemCIELAB system

L*L* 116(Y/Y 116(Y/Ynn))1/31/3 - 16 - 16

a*a* 500 500 ( X/X ( X/Xnn))1/31/3 - (Y/Y - (Y/Ynn))1/31/3

b*b* 200 200 (Y/Y (Y/Ynn))1/31/3 - (Z/Z - (Z/Znn))1/31/3

If If X/XX/Xnn > 0,008856 > 0,008856

Y/YY/Ynn > 0,008856 > 0,008856

Z/ZZ/Znn > 0,008856 > 0,008856

Brightness/luminanceBrightness/luminance

Colours of equal Colours of equal luminance might luminance might have different have different brightnessbrightness

Covan-Warren Covan-Warren experimentexperiment

Colour renderingColour rendering

Spectral power distribution

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Colour rendering under Colour rendering under different light sourcesdifferent light sources

Incandescent lamp, Incandescent lamp, and lamp with a and lamp with a neodymium neodymium containing bulb.containing bulb.

Colour rendering of Colour rendering of two metal-halid lamps two metal-halid lamps of different spectral of different spectral distributiondistribution

Spectral Band Methods Spectral Band Methods (SBM)(SBM)

Need to describe light source colour quality: Need to describe light source colour quality: Development of gas-discharge sources of Development of gas-discharge sources of different SPD but similar CCTdifferent SPD but similar CCT

First CIE recommendation: 1948 for an 8 band First CIE recommendation: 1948 for an 8 band SBM, deviation from full radiator.SBM, deviation from full radiator.

Crawford: 6 bands of comaprable weight in colour Crawford: 6 bands of comaprable weight in colour rendering, tolerances from ideal spectrum in the rendering, tolerances from ideal spectrum in the single bands.single bands. Comparing calculated values with visual obesrvations on Comparing calculated values with visual obesrvations on

picutrespicutres Museum lightingMuseum lighting

Bands: 400-455, 455-510, 510-540, 540-590, 590-Bands: 400-455, 455-510, 510-540, 540-590, 590-620, 620-760.620, 620-760.

New Working CommitteeNew Working Committee 1955: CIE established WC 1.3.2 with the 1955: CIE established WC 1.3.2 with the

following tasksfollowing tasks TerminologyTerminology Measuring method, compare:Measuring method, compare:

and simplify the 1948 8 band methodand simplify the 1948 8 band method test the test sample methodtest the test sample method

1961: test colour method decided1961: test colour method decided Agreement: 8 test samplesAgreement: 8 test samples

1964: test sample method agreed, without 1964: test sample method agreed, without chrom. Adaptation: Publ. 13, 1st edition chrom. Adaptation: Publ. 13, 1st edition

Present test sample Present test sample methodmethod

1974: Publ. 13 2nd edition1974: Publ. 13 2nd edition Definition on reference illuminant, Definition on reference illuminant,

tolerancestolerances Test samples: 8 + 6Test samples: 8 + 6 Von Kries chromatic adaptation Von Kries chromatic adaptation

transformtransform Use the CIE 1964 UCSUse the CIE 1964 UCS Scaling: WW halophosphate lamp should Scaling: WW halophosphate lamp should

have an Ra of 50.have an Ra of 50.

Post 1974 progressPost 1974 progress

Trials to define a flatery/preference indexTrials to define a flatery/preference index Problem: Problem:

The use of The use of RRaa to optimize the SPD of tri-band to optimize the SPD of tri-band fluorescent lampsfluorescent lamps

The new SPDs produced large negative indicesThe new SPDs produced large negative indices SolutionsSolutions

Non-liner scaling from 0 to 100Non-liner scaling from 0 to 100 Other methods (e.g. rout mean square) for Other methods (e.g. rout mean square) for

averaging averaging RRii-s-s

Problems of the CIE Test Problems of the CIE Test MethodMethod

Samples look different under low and high Samples look different under low and high CCT sources of equal CCT sources of equal RRaa, , break at 5000 K: break at 5000 K: Planck distribution Planck distribution at 4999 K: at 4999 K: RRaa = 100= 100 At 5001 K: At 5001 K: RRaa = 89= 89

Result depends on selection of test samplesResult depends on selection of test samples Von Kries transformation outdatedVon Kries transformation outdated U*,V*,W* space outdated, not colour U*,V*,W* space outdated, not colour

appearance spaceappearance space

Metameric Test SamplesMetameric Test Samples

Metameric samples:Metameric samples: CIE Test SampleCIE Test Sample Laser printer sampleLaser printer sample 2 Ink-Jet printer 2 Ink-Jet printer

samplessamples Rank order of some Rank order of some

lamps in case of CIE lamps in case of CIE Test Samples and Test Samples and different metameric different metameric matchesmatches

CIE TC 1-33CIE TC 1-33

Try to use a colour apperance modelTry to use a colour apperance model As progress for CAM was slow: update for As progress for CAM was slow: update for

post 1976 basic colorimetric knowledge:post 1976 basic colorimetric knowledge: New test samplesNew test samples Von Kries chrom.adapt.transform. Von Kries chrom.adapt.transform.

Nayatani transformationNayatani transformation

Transform to D65Transform to D65 UU**VV**WW* space * space LL**aa**bb* space* space

Proposed test samples in Proposed test samples in CIELAB spaceCIELAB space

•ProposeProposeddcalculatiocalculation stepsn steps

- use only a - use only a few few reference reference CCTsCCTs

- - not not acceptedaccepted- visual - visual resultsresults requestedrequested

CIE TC 1-62 report: CIE TC 1-62 report: NakanoNakano

Multispectral images – semantic Multispectral images – semantic differential evaluationdifferential evaluation

Principal component analysisPrincipal component analysis First factor – colourfullness, low First factor – colourfullness, low

correlationcorrelation Second factor – colour fidelity, good Second factor – colour fidelity, good

corelationcorelation

CIE TC 1-62 report: Davis CIE TC 1-62 report: Davis & Ohno & Ohno

Simulation of 15 test sample Simulation of 15 test sample appearance for 40 SPDsappearance for 40 SPDs

Question of gamut area – extreme Question of gamut area – extreme colour distortionscolour distortions

Proposed metric: Colour Quality Proposed metric: Colour Quality Scale Scale

Colour distortions under Colour distortions under different LED sourcesdifferent LED sources

Experiments at Uni.Pannonia Experiments at Uni.Pannonia (several other lab-s are (several other lab-s are

conducting experiments)conducting experiments)

Visual experiments Visual experiments in a double boothin a double booth

3 main CCT groups3 main CCT groups 2700 K2700 K 4000 K4000 K

Lamps:Lamps: IncandewscentIncandewscent FluorewcentFluorewcent RGB- and p-LEDsRGB- and p-LEDs

Colour Colour appearancappearance e in case of in case of incandesceincandescent lamp nt lamp and LEDand LED

Incandescent

LED

Correlation coefficients between Correlation coefficients between visually observed and calculated colour visually observed and calculated colour

differencesdifferences

4000 K 4000 K CCT groupCCT group R-(U*V*W*)R-(U*V*W*) R-(CIELAB)R-(CIELAB)

R-R-(CIECAM02(CIECAM02

))

LED LED cluster1cluster1

0,820,82 0,820,82 0,890,89

LED LED cluster2cluster2 0,750,75 0,740,74 0,790,79

CoolWhite CoolWhite fl.lampfl.lamp 0,690,69 0,500,50 0,750,75

White LEDWhite LED -0,50-0,50 -0,37-0,37 0,040,04

Correlation (R value) between visual Correlation (R value) between visual scaling and CIE 13.2,CIELAB and scaling and CIE 13.2,CIELAB and

CIECAM02 based modelCIECAM02 based model

Light sourceLight source CIE 13.2CIE 13.2 CIELABCIELAB CIECAM02CIECAM02

CoolWhite CoolWhite CFL(940)CFL(940)

-0,39-0,39 -0,42-0,42 -0,29-0,29

CoolWhite CoolWhite CFL(840)CFL(840)

0,670,67 0,570,57 0,640,64

CoolWhite Fl., CoolWhite Fl., tradit.tradit.

0,690,69 0,500,50 0,750,75

CoolWhite Tri-CoolWhite Tri-bandband

0,490,49 0,470,47 0,600,60

P-LEDP-LED -0,62-0,62 -0,37-0,37 0,040,04

RGB-LED 1RGB-LED 1 0,750,75 0,740,74 0,790,79

RGB-LED 2RGB-LED 2 0,820,82 0,820,82 0,890,89

Recommendations by TC Recommendations by TC 1-621-62

Use MCC test samples (TC 1-33 Use MCC test samples (TC 1-33 recommendation)recommendation)

Consider task dependent reference Consider task dependent reference illuminants for task dependent Colour illuminants for task dependent Colour Quality MetricQuality Metric

Try CIECAM02 based colour difference Try CIECAM02 based colour difference formulaformula

Take preference, visual clarity into Take preference, visual clarity into considerationconsideration

Current activity on Current activity on colour qualitycolour quality

Colour fidelityColour fidelity Colour preferenceColour preference Colour harmony distortionColour harmony distortion Colour Colour discriminationdiscrimination Arousal by colourArousal by colour Visual comfortVisual comfort

Simulation experimentSimulation experimentDescription of Description of light sourcelight source

Correlated colour Correlated colour temperature, Ktemperature, K RaRa

CIE ACIE A 28562856 100100

CIE D65CIE D65 65056505 100100

FL 3.5FL 3.5 40864086 9696

FL 3.12FL 3.12 29842984 9393

FlLampFlLamp 72267226 8787

CIE FL 7CIE FL 7 64976497 8686

CIE FL 11CIE FL 11 39993999 8383

p-LED (cool)p-LED (cool) 93109310 8080

p-LED (wrm)p-LED (wrm) 29762976 7777

CIE FL 2CIE FL 2 42254225 6464

CIE FL 4CIE FL 4 29382938 5151

RGB-LED1RGB-LED1 27882788 4444

RGB-LED2RGB-LED2 27882788 2727

RGB-LED3RGB-LED3 27882788 -17-17

Hyperspectral images used Hyperspectral images used in the experimentin the experiment

Task in the experimentTask in the experiment

Results of the simulation Results of the simulation on CRT monitoron CRT monitor

Ra versus Visual scaling for two pictures „illuminated” with a number of sources, transformed to the same white point.

Colour quality descriptor, Colour quality descriptor, preferencepreference

Harmony distortion: the average colour differences are Harmony distortion: the average colour differences are the same in the two copies (McCann’s observation)the same in the two copies (McCann’s observation)

Second test: preference, Second test: preference, which image do you which image do you

prefer?prefer?

Chromaticity distortionsChromaticity distortions Color coordinates Color coordinates

of a Munsell of a Munsell harmonious set harmonious set called “Diminishing called “Diminishing series” under a series” under a reference illuminant reference illuminant (blue squares), and (blue squares), and under a white RGB under a white RGB LED light source LED light source

(pink circles).(pink circles).

Further factorsFurther factors

Regional preference for CCTRegional preference for CCT Task related preference for CCTTask related preference for CCT

Home – relaxing: ~ 3000 K ?Home – relaxing: ~ 3000 K ? Office – stimulating: ~ 4000 KOffice – stimulating: ~ 4000 K Colour discrimination: 6500 KColour discrimination: 6500 K

Visual clarity, visual comfort ?Visual clarity, visual comfort ? Circadian rhythm dependence?Circadian rhythm dependence?

Circadian rhythm and Circadian rhythm and lightinglighting

Daily rhythm: arousal – Daily rhythm: arousal – melatonin suppressionmelatonin suppression

Influencing with lighting?

c():circ. efficiency function

harmful effects?

C ( ) dF S c not prooved yet!

Spectrum influences the circadian Spectrum influences the circadian efficiency/luminous output (efficiency/luminous output (CC) )

ratioratio

C

( ) d

( ) d

S c

S V

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lue

s

Ill.A: 0.37/100

C/L: 0.34/34

C/L: 0.35/48

C/L: 0.38/80

C/L: 0.38/86

C/L: 0.43/34

C/L: 0.43/39

y2(l)

Circa-dianSp

Illuminant C RaA 0.37 100

LED1 0.34 34LED2 0.35 48LED3 0.38 80LED4 0.38 86LED5 0.43 34LED6 0.43 39

cc(():circ. efficiency function):circ. efficiency function VV(()-function)-function

Summary of visual issues Summary of visual issues on the use of LEDs in on the use of LEDs in

lightinglighting Use updated colour matching Use updated colour matching

functions to calculate chromaticity of functions to calculate chromaticity of LEDsLEDs

Be carefull with colour rendering Be carefull with colour rendering index, new descriptors are neededindex, new descriptors are needed

Design illuminants that can adapt to Design illuminants that can adapt to lighting situations: daylight lighting situations: daylight supplementary light / calming supplementary light / calming comfort lightingcomfort lighting

LEDs used in projectionLEDs used in projection

NTSC and EBU NTSC and EBU colour gamut not colour gamut not large enough for large enough for reproducing every reproducing every surface coloursurface colour

CCFL gamut even CCFL gamut even smallersmaller

RGB LEDs provide RGB LEDs provide larger gamutlarger gamut

LEDs versus CCFL in LEDs versus CCFL in backlightingbacklighting

Measurement technical Measurement technical issuesissues

LEDs are narrow band emittersLEDs are narrow band emitters bandwidth approx. 10 nm – 30 nmbandwidth approx. 10 nm – 30 nm Blue … Green: InGaNBlue … Green: InGaN Yellow … Red: AlInGaPYellow … Red: AlInGaP

Both the absolute intensity and the Both the absolute intensity and the wavelength of the emission maximum is wavelength of the emission maximum is temperature dependenttemperature dependent temperature dependence is composition temperature dependence is composition

dependent dependent largest changes with Red LEDslargest changes with Red LEDs

Unusual spatial light characteristicsUnusual spatial light characteristics

Typical LED spectraTypical LED spectra(used in optimization, see (used in optimization, see

later)later)

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TT-LED-11-1

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TT-LED-9-1

TT-LED-8-1

TT-LED-10-1

TT-LED-OLD2-1

TT-LED-OLD1-1

LED colour LED colour characteristicscharacteristics


Both the absolute intensity and the Both the absolute intensity and the wavelength of the emission maximum is wavelength of the emission maximum is temperature dependenttemperature dependent temperature dependence is composition dependent temperature dependence is composition dependent largest changes with Red LEDslargest changes with Red LEDs

Unusual spatial light characteristicsUnusual spatial light characteristics Solution of measurement problems caused bySolution of measurement problems caused by

Spectral mismatch: spectrometric measurementSpectral mismatch: spectrometric measurement Spectral mismatch: tristimulus colorimetrySpectral mismatch: tristimulus colorimetry Temperature dependence Temperature dependence Geometric misalignmentGeometric misalignment

Temperature dependence Temperature dependence of a blue LEDof a blue LED

Blue

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rel.

int.

3 °C

21 °C

34 °C

50 °C

Temperature dependenceTemperature dependenceof a yellow LEDof a yellow LED

YL 3

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550 600 650

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rel.

in

ten

sit

y

22,4°C

36,3°C

46,8°C

56,8°C

Temperature dependence Temperature dependence of a red LEDof a red LED

Temperature dependenceTemperature dependenceof a white LEDof a white LED

WT 2

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22,9°C

33,7°C

54,3°C

67,5°C



Both the absolute intensity and the wavelength Both the absolute intensity and the wavelength of the emission maximum is temperature of the emission maximum is temperature dependentdependent temperature dependence is composition dependent temperature dependence is composition dependent largest changes with Red LEDslargest changes with Red LEDs



Irradiation Irradiation inhomogeneity in inhomogeneity in

measurement planemeasurement plane

What should be reported?

Problem of reproducible alignment



Both the absolute intensity and the Both the absolute intensity and the wavelength of the emission maximum is wavelength of the emission maximum is temperature dependenttemperature dependent temperature dependence is composition dependent temperature dependence is composition dependent largest changes with Red LEDslargest changes with Red LEDs



Spectrometric Spectrometric measurementsmeasurements

Critical parameters of spectrometerCritical parameters of spectrometer Sampling interval and bandpass: 10 nm sampling Sampling interval and bandpass: 10 nm sampling

produces produces uu’,’,vv’ errors of several units in 3rd ’ errors of several units in 3rd decimal.decimal.

Highly oversampling OK (CCD spectrometers)Highly oversampling OK (CCD spectrometers) Wavelength scale error: 0.5 nm error produces Wavelength scale error: 0.5 nm error produces

uu’,’,vv’ errors of several units in 3rd decimal.’ errors of several units in 3rd decimal. Stray light: LED measurement compared to Stray light: LED measurement compared to

incandescent lamp if 10incandescent lamp if 10-4-4 stray light produces stray light produces uu’,’,vv’ errors of several units in 3rd decimal.’ errors of several units in 3rd decimal.

Experiments showed even larger errors:Experiments showed even larger errors:

Comparison of 5 Comparison of 5 spectrometersspectrometers

Green LED chromaticityGreen LED chromaticity


Red LED chromaticityRed LED chromaticity

0,2940

0,2942

0,2944

0,2946

0,2948

0,2950

0,2952

0,2954

0,7030 0,7040 0,7050 0,7060

x

y

NIST 5 nm

Single mon.

Double mon.

High end CCD

Low end CCD


Blue LED chromaticityBlue LED chromaticity

0,114

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0,130

0,114 0,115 0,116 0,117 0,118

x

y

NIST 5 nm

Single mon.

Double mon.

High end CCD

Low end CCD

One of the problems is One of the problems is stray lightstray light

Spectrum of a Spectrum of a green laser green laser semiconductosemiconductor laserr laser

Enlarged view Enlarged view of the lower of the lower 0.1% of the 0.1% of the emission emission curvecurve

50ms

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300x







Goodness of fit Goodness of fit characterizationcharacterization

Modified Modified ff11’ method,’ method, No illuminantNo illuminant Independently forIndependently for

Separately for Red, Separately for Red, Green, Blue LEDsGreen, Blue LEDs Example: Example: VV(() channel) channel Use coloured LED Use coloured LED

standardsstandards ff11’ provides estimate of ’ provides estimate of

error to be expectederror to be expected Detector spectral Detector spectral

responsivity responsivity measurement, not measurement, not standardized properlystandardized properly

rel,

01,

0

*( ) ( ) d

' 100%

( ) d

i i

i

i

s t

f

t

s l( ), ( ), ( ), ( )x x y z

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rel.

se

ns

itiv

ity

f1'=1.33

f1'=1.97

V(l)

Partial Partial ff11’ error index 1’ error index 1

LED dominant wavelength ranges andLED dominant wavelength ranges andthe dominant wavelength value of the standard LEDs the dominant wavelength value of the standard LEDs

Correcting tristimulus colour Correcting tristimulus colour measurement of LEDs by matrix measurement of LEDs by matrix

transformationtransformation Modern tristimulus colorimeters have Modern tristimulus colorimeters have

four input channels. One canfour input channels. One can just add the signals of the xjust add the signals of the xss and x and xll

channels (no matrixing)channels (no matrixing) Use the four channels for improving Use the four channels for improving

accuracyaccuracy Add a fifth channel Add a fifth channel

Optimization was performed for the Optimization was performed for the LEDs shown previouslyLEDs shown previously

Experimental five filter Experimental five filter colorimeter spectral colorimeter spectral

responsivityresponsivity

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re

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ity

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xms

xml

ym

zm

km

Average Average colorimetric colorimetric

errors for the errors for the eight LEDseight LEDs

Matrix typeMatrix typeColorimetric Colorimetric

error, Δerror, ΔEEabab**

Without Without matrixingmatrixing

9,679,67

4 filter 4 filter matrixmatrix

3,763,76

5 filter 5 filter matrixmatrix

1,091,09

0.00

0.20

0.40

0.60

0.80

1.00

400 500 600 700 800

wav elength, nm

rel.

in

ten

sit

y

TT-LED-11-1

TT-LED-12-1

TT-LED-13-1

TT-LED-9-1

TT-LED-8-1

TT-LED-10-1

TT-LED-OLD2-1

TT-LED-OLD1-1







Standard LEDStandard LED

Temperature Temperature and current and current stabilized stabilized LED for LED for luminous luminous flux flux measurememeasurementnt

Standard LEDStandard LED

Temperature Temperature and current and current stabilized stabilized LED for ALI LED for ALI measurememeasurementnt






Spectral mismatch: spectrometric measurementSpectral mismatch: spectrometric measurement Spectral mismatch: tristimulus colorimetrySpectral mismatch: tristimulus colorimetry Temperature dependenceTemperature dependence Geometric misalignmentGeometric misalignment

ALI measurementALI measurement

Input clamp Input clamp of ALI tubeof ALI tube

• Clamp for 5 mm LED

Degradation – life timeDegradation – life time Degradation Degradation

highly highly dependent on dependent on junction junction temperaturetemperature

0

20000

40000

60000

80000

100000

120000

0 20 40 60 80 100 120Junction Temperature (deg C)

Life

(hrs

)

5 mm White LED

0

20

40

60

80

100

120

0 2000 4000 6000 8000 10000 12000Time (hrs)

Rel

ativ

e L

igh

t O

utp

ut

(%)

20 mA 30 mA 40 mA 50 mA 60 mA

Flux and thermal Flux and thermal measurementmeasurementReference LED

Standard LED

DUT LED

Detector with different filters

TeraLED complex colorimetric and thermal measuring system

•Radiometric•Photometric•Colorimetric•Thermal measurements

Technical summaryTechnical summary

Current sate of the art in user’s Current sate of the art in user’s laboratory:laboratory:

Spectral mismatch uncertainty: 1 – 2 %Spectral mismatch uncertainty: 1 – 2 % Geometric alignment uncertainty: <+/-Geometric alignment uncertainty: <+/-

0,002%0,002% Temperature dependence: +/- 0,2 %Temperature dependence: +/- 0,2 %

Application of LEDs in Application of LEDs in automotive lightingautomotive lighting

Interior lightingInterior lighting White light of low luminance, but good visibility: White light of low luminance, but good visibility:

high correlated colour temperature (arousal)high correlated colour temperature (arousal) Signalling: Signalling:

Coloured LEDs are the most efficient coloured Coloured LEDs are the most efficient coloured light sourceslight sources

Problems with stroboscopic effect – current Problems with stroboscopic effect – current sourcesource

HeadlampsHeadlamps Visibility – glareVisibility – glare Colour of illuminated objects - renderingColour of illuminated objects - rendering

Interior lightingInterior lighting

Provide efficient lighting to see Provide efficient lighting to see detailsdetails 30 lx to 50 lx30 lx to 50 lx Higher CCT provides better visibility at Higher CCT provides better visibility at

low light levelslow light levels Arousal increases with CCTArousal increases with CCT

SignallingSignalling Automotive bond signal Automotive bond signal

lightslights Good efficiency & long Good efficiency & long

life with LEDslife with LEDs Stroboscopic effects to Stroboscopic effects to

be avoidedbe avoided Road bond signal lightsRoad bond signal lights

Visibility in case of Visibility in case of partial source drop outpartial source drop out

Sun phantom avoidanceSun phantom avoidance Luminance bad Luminance bad

descriptor of coloured descriptor of coloured light visibility – optimal light visibility – optimal luminance should be reluminance should be re--determined determined

Car Headlamps, human Car Headlamps, human factorsfactors

Good visibilityGood visibility Mesopic visibilityMesopic visibility Additive of Additive of V V ’(’() and ) and VV(()?)? Contribution of colour channelsContribution of colour channels X and MOVE modelsX and MOVE models

Low glareLow glare Do sources with higher CCT glare more?Do sources with higher CCT glare more?

Spectral measurementsSpectral measurements

Mesopic spectral Mesopic spectral responsivityresponsivity

Influence of Influence of chromatic chromatic channels channels obviousobvious

Glare spectrum, laboratory Glare spectrum, laboratory experimentexperiment

V V ’(’() + ) + VV((): no good fit): no good fit L,M,S cone fundamental L,M,S cone fundamental

based model describes based model describes wellwell

SummarySummary

Application of LEDs Application of LEDs Produce some fundamental colorimetric Produce some fundamental colorimetric

questionsquestions Have their practical measurement Have their practical measurement

problemsproblems LEDs now ripe for automotive applicationsLEDs now ripe for automotive applications

Proper thermal management is fundamentalProper thermal management is fundamental

Questions and discussionQuestions and discussion

Documents

Colorimetry of Solid State Light Sources