lighting technologies principle and measurement

SENS ING AMER ICAS, INC.

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LightingTechnologies,Principle,andMeasurement


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Lighting Technologies Principle and Measurement2 ColorRenderingProperties

2 ColorTemperature

2 LightDistribution

2 TotalLuminousFlux

2 Mura(Nonuniformity)

Color-Rendering Properties3 Fluorescent,naturalwhite,&LEDs

Color Temperature6 ColorTemperature

7 DifferencesfromColorTemperatureMeasured

UsingaPhotographicColorimeter

Light Distribution9 Lightsources

9 HowtoMeasureLightDistribution

10 LightDistributionMeasurementDevice

Total Luminous Flux

11 Luminousflux

11 HowtoMeasureTotalFlux

12 TotalFluxMeasurementDevice

Mura13 Mura

13 MuraStandards

13 SEMU

13 JEITA

13 CurrentMeasurementMethods

14 Sensorwithsensitivityneartothatofthe

humaneye

14 High-resolutionCCD

14 LowsensitivityerrorperCCDpixel

14 MeasurementDevice

14 ExampleMeasurementResults

Contents


2

Color Rendering Properties

Learnwhatcolor-renderingpropertiesareandseeforyourselfthe

relationshipbetweencolor-renderingindexesandhowsamples

lookunderdifferentlightsources.

Color Temperature

Learnthecorrelationbetweencolorandtemperature,and

seethedifferencefromcolortemperaturesmeasuredusinga

photographiccolormeter.

Light Distribution

Learnwhatlightdistributionisfromreal-lifeexamplesandsee

howtomeasureit.

Total Luminous Flux

Learnwhattotalfluxisandseehowtomeasureit.

Mura (Nonuniformity)

Learnaboutmurastandardsandcurrentmeasurementmethods.

Also,seesomeexamplesofmeasurementresultsobtainedusing

ameasuringinstrument.

LIGHTING TECHNOLOGIES, PRINCIPLE, AND MEASUREMENT

LIGHTIN

GTECHN

OLO

GIES,PRIN

CIPLE,AND

MEASUREM

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3

Totheeye,theyallseemwhitebutthenaturalwhitefluorescent

lamphasaslightlyhighercolor temperatureandlooksslightly

bluish.

Wemeasuredthethreelightsourcesbymountingaluminanceadapteronthe

KonicaMinoltaSpectroradiometerCS-2000.Ifyoucomparethemeasured

pointsonthexychromaticitydiagramatright,youcanseethatthetonesare

similarandinthevisiblerange.

COLOR-RENDERING PROPERTIESSincelongago,manhascomparedcolorsbyarrangingobjectsside-by-sideandlookingatthemundernaturallight

(sunlight).Althoughtorches,candles,incandescentlampsandotherlightsourcesarealsousedforillumination,ithasalways

beenthestandardpracticetocomparecolorsundernaturallight.

Inadditiontofluorescentlamps,LEDs(lightemittingdiodes)haverecentlybeenadoptedasilluminatinglamps.When

comparinghowobjectslookunderthesenewtypesoflampsagainsthowtheylookundernaturallight,howcloselythey

matchiscalledthe“color-renderingproperty.”Alampthatproducesahuesimilartothatofnaturallightissaidtohavea

good(high)color-renderingproperty.

Today,appliancestoresoffermanytypesoflamps(incandescent,fluorescent,LED,etc).Further,fluorescentlampsandLED

lampscomeintoneslike“white,”“warmwhite,”etc.

Intheexampleshere,weilluminatedanobjectwithaD50fluorescentlampwithgoodcolor-renderingproperty,afluorescent

lampthatwaslabeledas“Naturalwhite”andanLEDlamp.

2000

1500

250030003500

40004500

10000

D55

A

B

CD65

D75

520

510

500

490

480

470460

450

530

540

550

560

570

580

590

600

610620

650

380~440

680~780

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0.000.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Thehuechangesunderdifferentlightintg

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R-REND

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PROPERTIES


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Next,let’silluminaterawmeatwiththethreelightsources

andseehowthemeatlooks.

UndertheD50fluorescentlamp,themeatandtheplatelook

liketheyactuallydo,butunderthenaturalwhitefluorescent

lamp,thecolortemperatureisslightlyhigherandboththe

meatandtheplatelookslightlypaler.UndertheLEDlamp,

everythingisdarker.

•Theluminanceatthesamplesurfacewasadjustedtobe

about1600luxforallthreelightsources.

•Whenasampleisilluminatedwithdifferentlightsources,

thecolormaylookdifferent.

•Thedifferenceinlampperformanceiscalledusinga“color-

renderingindex.”

•Thisindexindicateshow15testcolorslookundera

particularirradiatedlight.

•Whencomparingalightsourceagainstastipulated

referencelightsource,anindexof100isthebest.

*Becauseofitslowcolor-renderingindex,theLEDlampusedthis

timemadethemeatandplatelookdark,butthemeatandplatecanlook

fresherwithanLEDlamphavingahighercolor-renderingindex.

X

Y

Correlatedcolor

temperature

D50 fluorescent lamp

0.3407

0.3518

5173

Natural white fluorescent lamp

0.3372

0.3496

5308

LED lamp

0.3465

0.3662

5004

SpectraldistributionofD50fluorescentlamp,naturalwhitefluorescentlampandLEDlampRelativeintensity

aD50 Naturalwhitefluorescentlamp fluorescentlamp LEDlamp

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Weobtainedthefollowingcolor-renderingindexesfromthespectraldistributionmeasuredwithaSpectrophotometerCS-

2000modifiedforluminancemeasurement.ItcanbeeasilycomputedusingtheDataManagementSoftwareCS-S10wfor

theCS-2000.

Raisthe“meancolor-renderingindex.”Itistheaverageofindexes

R1~R8andisarepresentativevalueofcolor-renderingindexes.

R9~R15aretermed“specialcolor-renderingindexes,”withparticular

interestoftenbeingshowninR9(highlyvividred)andinR15.

R9isusedforevaluationofthereproductionofred,andthebig

differencesinvaluesbetweenthethreetypesoflightsourcesalsogive

anindicationofhowmuchthecolorofthemeatseenunderthedifferent

lightsourceswillvary.



LED lamp

Ra

91

79

68

R1

94

89

65

R2

91

89

74

R3

86

54

79

R4

90

82

68

R5

93

81

65

R6

89

72

62

R7

90

86

81



LED lamp

R8

90

76

54

R9

77

16

-39

R10

78

40

36

R11

93

63

61

R12

81

55

31

R13

93

92

66

R14

92

70

88

R15

91

92

59

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COLOR TEMPERATURE

Asyouknow,thetwinkling(fixed)starsintheevening

skyhaveafaintcolor.Itisalsoknownthatthesurface

temperatureofbluishstarsishigherthanthesurface

temperatureofreddishstars.

Blacksmithsjudge

thetemperature

ofahotironfrom

itscolor(red).This

shouldgiveyouan

ideathatsomesort

ofcorrelationexists

betweencolorand

temperature.

Anidealradiator(blackbody)absorbsallexternal

electromagneticradiationandre-emitstheradiation.Asthe

temperatureofablackbodyincreases,itchangescolorinthe

orderofred→yellow→white→bluewhite.

Ifthischangeincolorduetotemperatureisplottedonanxy

chromaticitydiagramasshowntotheright,itlookslikethe

blackcurvedlineinthelowercenterofthediagram.Thisline

iscalledthe“blackbodylocus”andthecolortemperatureson

thislinearecalled“absolutecolortemperatures.”

Butnotallexistinglightsourcesareonthisblackbodylocus.

Infact,mostlightsourceshavingawhitechromaticitypoint

areslightlyoffofthisblackbodylocus.Insuchcases,the

colortemperaturecanbeobtainedusingtheisotemperature

linesdrawnacrosstheblackbodylocus.Thecolor

temperatureisthenreferredtoas“correlatedcolor

temperature.”

red→yellow→ white→bluewhite

COLO

RTEMPERATURE


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Colortemperatureandcorrelatedcolortemperatureare

generallyusedasanindextorepresentcolorswithinarange

ofwhite(reddishwhite,yellowishwhite,whiteandbluish

white)andcanbemeasuredwithourChromaMeterCL-200/

CL-200A(forilluminanceandchromaticitymeasurement),

ChromaMeterCS-200(forluminanceandchromaticity

measurement),SpectroradiometerCS-2000/2000Aand2D

ColorAnalyzerCA-2000.

DIFFERENCESFROMCOLORTEMPERATUREMEASUREDUSINGAPHOTOGRAPHICCOLORIMETER

Photographiccolorimeters

areseparatefromtheabove

industrial-grademeasuring

instruments.Althoughthey

claimtomeasurecolor

temperature,thepurposeisto

determinetheappropriatefilter

valuesfortakingpictures.The

colortemperaturetakenwith

suchcolorimetersiscalled“photographiccolortemperature.”

Althoughthesensorsoftheindustrialinstrumentsdescribed

earlierareintendedtocloselymatchthesensitivityofthe

humaneye,thesensorsofphotographiccolorimetersare

similartothesensitivityofcolorphotographicfilm.

Fig.1belowontheleftshowsthesensitivityofthehuman

eye,andFig.2belowontherightshowsthesensitivity

ofcolorphotographicfilm.Youcanseethattheyare

completelydifferent.

Becauseofthis,if,forexample,thecolortemperatureof

thesamelightsourcewasmeasuredwithaChromaMeter

andaphotographiccolorimeter,theresultwouldbetwo

completelydifferentvalues.

Whenmeasuringcolortemperatureforpurposesother

thantakingpictures,anindustrialmeasuringinstrumentis

needed.

COLO

RTEMPERATURE


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Asareference,thegraphsbelowshowtheresultsofacomparisonbetweenthecorrelatedcolortemperatureofawhiteLED,

coloredLEDandfluorescentlamp(warmwhite,naturalwhiteanddaylightwhite)measuredusingourSpectroradiometer

CS-2000+Luminanceadapterandthecolortemperaturemeasuredusingaphotographiccolorimeter.Thehorizontalaxisis

thecorrelatedcolortemperaturemeasuredusingourSpectroradiometerandtheverticalaxisisthedifferenceinmeasured

valuesbetweenthespectroradiometerandphotographiccolorimeter.

Youcanseethattherearewidedifferencesinmeasuredvalueswithsomelightsources.Thecorrelatedcolortemperature

measuredusingtheSpectroradiometeris,inprinciple,neartothetruevalue.Butitshouldbenotedthatthisisjustone

example.Itisnotguaranteedthatthesameresultswouldbeobtainedifadifferentphotographiccolorimeterwereusedor

evenifthesamesampleweremeasuredusinganotherphotographiccolorimeterofthesamemodelasthatusedthistime.

Relatedstandard:JISZ8725MethodsforDeterminingDistributionTemperatureandColorTemperatureorCorrelatedColorTemperatureofLightSources

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RTEMPERATURE


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LIGHT DISTRIBUTION

Alllightsourcesemitlight,butinwhatdirection(angle)that

lighttravelsandhowstrongitisarecollectivelydescribedas

the“lightdistribution.”

Lightdistributionpropertiesareusedtodeterminewhatlight

sourcewouldbegoodfor,forexample,astronglydirectional

lightoradiffusedlight.Withlightingfixturesandthelike,

theyaresimilarlymeasuredandevaluatedtogetherwithlight

sources,shades,backgrounddeflectorpanels,etc.

“Lightdistribution”isdefinedinJISZ8113“Lighting

Vocabulary.”Thatdefinitionreads:“theangularchangeor

distributionofluminosityofprimarylightsources,secondary

lightsources(includinglighttransmissionandreflectionof

opticalmaterials,etc.)andlightingfixtures.”Asexamples,

Fig.1ontheleftaboveshowsthemeasuredlightdistribution

ofabulletLEDandFig.2ontherightaboveshowsthesame

forasurfacemountedLED.

Withfluorescentfixtures,thelightdistributionactually

includestheeffectofpartsotherthanthebulb.

Onemethodforcategorizinglightdistributionisthe

internationalmethod.Itdefinesthelightdistributionas

theratioofupwardmovingfluxfromthelightsourceto

thedownwardmovingflux.Inthiscategory,thefixture’s

configurationcanbeaddressedandaroughideaofthe

utilizationfactor,animportantfactorinlightingdesign,can

beunderstood.

HOWTOMEASURELIGHTDISTRIBUTION

Lightingdistributionmeasurementisbasicallydividedinto

twoapproaches.Oneistopositionsensorsacertaindistance

fromasampleandmeasurethelightdistribution.Inthis

case,resultsareobtainedbymeasuringfrommultiplepoints

concentricallylocatedaroundthesample

LIGHTD

ISTRIBUTION


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Theotherapproachistomeasuredistributionatdifferent

distancesfromthesampleusingameasuringdevice

consistingofaCCDsensorandanopticalsystemwithan

extremelywide-anglelenssimilartoafisheyelens.

LIGHTDISTRIBUTIONMEASUREMENTDEVICE

Konica-Minoltacreatedacustomizedlightdistribution

measurementdevicewithamovingsensortomeet

customers’needs.Inaddition,threetypesofsensorscan

beused:spectroradiometricsensor,colorimetricsensorand

luminancesensor.

Illustration

Merits

Demerits

Moving Sensor

•Anglepitchandsensordistancecanbefreely

set.

•Lessexpensivethanastationarysensor

setup

•Longtimerequiredtocompleteall

measurements

Stationary Sensor

•Shorttimerequiredtocompleteall

measurements

•Moreexpensivethanamovingsensorsetup

•Restrictedbysampleshapeandsize

Source:TextbookforLightingFundamentalsClass,Illumi-natingEngineeringInstituteofJapan

LIGHTD

ISTRIBUTION


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TOTAL LUMINOUS FLUXLuminousfluxisavalueforevaluatingtheradiantfluxbasedonthespectralluminousefficiencyfunctionofthehumaneye

andthemaximumluminousefficacy.Totalfluxistheluminousfluxradiatedinalldirectionsfromalightsourceanditisused

asameasureofbrightnessforlightingfixtures.ItsunitsareLumens(lm).

Theterms“luminosity”and“brightness”areoftenheardtoexpressaquantityoflight.Bothofthesetermsincludethe

meaningofdirectionality.Totalfluxdoesnothaveanyconnotationofdirectionality.

ΦV=Km・∫Φe(λ)V(λ)dλ

ΦV:Luminousflux

Km:Maximumluminousefficacy

φe(λ):Radiantflux

V(λ):Spectralluminousefficiency

＜Examples＞

Sunlight:Approx.3.6×1028lm

37Wfluorescentlamp(White):Approx.3,100lm

95Wwhiteincandescentbulb:Approx.1,520lm

Totalfluxisusedincalculationswhendesigninglightingfixtures.“Luminousefficacyofalamp,”obtainedbydividingthe

luminousfluxbytheelectricalpower(powerconsumption),hasalsobeenusedfromanecologicalperspectiverecently.

HOWTOMEASURETOTALFLUX

Therearetwowaystomeasuretotalflux:byusinganintegratingsphereorbylightdistributionmeasurement.Theintegrating

spheremethodplacesasamplelightsourceinanintegratingsphere(aspherethatishollowwiththeinnerwallpainted

ahighlydiffusivewhitecolor)andreceivingthelightwithasensor.Inthiscase,thesensormustbecalibratedagainsta

referencelightsource.

Withthelightdistributionmeasurementmethod,thesensorismovedconcentricallyaroundthesampleatasetdistance,and

thelightingdistributionismeasured.

TOTALLUM

INO

USFLUX


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TOTALFLUXMEASUREMENTDEVICE

Konica-MinoltaSensingofferscustomizedintegratingsphereandlightdistributionmeasurementsystemstomeetcustomer

needs.(ContactKonica-MinoltaSensingformoreinformation.)

Fortheintegratingspheremethod,spheresizesfrom6to40inchesindiameterareavailable.

Approach

Illustration

Merits

Demerits

Integrating Sphere

•Measurementscanbedoneinashortamount

oftime.

•Simplestructure

•Sensormustbecalibratedagainstareference

lightsource.

•Self-absorptioncausedbydifferencesin

shapefromthereferencelightsourcemustbe

compensatedforinmeasurements.

Light distribution measurement

•Lightdistributionpropertiescanalsobe

understood

•Longtimerequiredtocompleteall

measurements

•Notsuitedforsamplesthatradiatelightinall

directions

TOTALLUM

INO

USFLUX


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MURA

Withthelargerprojection

TVsandprojectorsof

recentyears,uneven

luminanceandchromaticity

indisplayedimagesreadily

standout.“Mura”isaterm

usedtodescribethenonuniformityperceivedwhenaperson

looksatadisplay.

Luminancecross-section(Luminancedistributionofdisplay

seeninasingledimension)Perceivedunevenpoints,inthe

abovediagram.

Unevenluminanceandchromaticityareeachbelieved

tobecausedbymultiplefactorssuchascontrast,area,

etc.Addtothistheverybigfactorofhumanvisionandit

becomesverydifficulttodefineitclearly.

MURASTANDARDS

1. SEMU

Despitethedifficultyofdefiningmura,the“SEMU”definition

wasstandardizedin2002.Shortfor“SEMIMuraUnit,”itwas

standardizedasaunitofmeasurementbySEMI*.Itapplies

notonlytoLCDsbutalsotoFPDs.Measurementrequires

a2-dimensionalcolorimeterthatnotonlyrequiressample

luminancetobemeasuredbutalsothesizeofthemura

area.

*AcronymforSemiconductorEquipmentandMaterials

International,anonprofitindustrialorganizationtowhich

world-prominentmanufacturersofsemiconductors,flatpanel

displaysandassociatedmaterialsbelong.

2. JEITA

EIAJED-2810“MeasuringMethodsforOrganicELDisplay

Modules”releasedin2000bytheJapanElectronicsand

InformationTechnologyIndustriesAssociation(JEITA)

containsmethodsformeasuringluminanceuniformityand

whitechromaticityuniformity.However,theyarebasedon

measuredluminanceandchromaticityvaluesofanH3x

V3(9points)displayarea;thereforethemethodsarenot

effectiveformeasuringmuraoutsideofthese9points.

CURRENTMEASUREMENTMETHODS

Currentlytherearenostandardizedrulesformeasuring

mura,buttoobtainsomesortofobjectiveevaluation,itis

bettertoperform2-dimensionalmeasurementsofluminance

andchromaticityusingCCDsensors.A2-dimensional

colorimeterforthispurposerequiresthefollowingfunctions

andperformance.

SENSORWITHSENSITIVITYNEARTOTHATOFTHEHUMAN

EYE

OrdinarycolorCCDshavedifferentsensitivitiesthanthe

humaneyedoes,makingitdifficulttomeasureluminance

andchromaticitycorrectly.

HIGH-RESOLUTIONCCD

Witharesolutionof200×200,forexample,theluminance

variationsofsmallareascannotbecaptured.

MURA


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LOWSENSITIVITYERRORPERCCDPIXEL

IfmuraoccursinthesensitivityofindividualCCDpixels,theluminancedistributionandchromaticitydistributioncannotbe

accuratelymeasured.

MEASUREMENTDEVICE

Konica-Minoltadevelopedthe2DColorAnalyzerCA-2000Awitharesolutionof980x980,withsensorsensitivitynearto

thatofthehumaneyeandminimalsensitivityerrorperCCDpixel.Thedrivesoftwareincorporatesafunctionforaccentuating

mura.Thisfunctionobtainstheaveragemuraofanareaofaset

sizearoundeachmeasurementpointandusesittosmooththe

data.Itdisplaystheratioofeachmeasurementpointdataand

averageddataas2-dimensionalresults.Therefore,whensample

luminanceisuniform,itaccentuatesanywherewithinthedisplay

whereluminanceisloworhigh.

EXAMPLEMEASUREMENTRESULTS

A:Luminancecross-sectionB:MovingaverageofAC:A/B

MURA

lighting technologies principle and measurement

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