Relation between the illuminance responsivity of a photometer and the spectral power distribution of a source

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Optical Engineering 46�9�, 093607 �September 2007�

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elation between the illuminance responsivityf a photometer and the spectral poweristribution of a source

erhat Sametoglu, MEMBER SPIE

ational Metrology Institute of Turkey�TÜBITAK-UME�

1470 Gebzeocaeli, Turkey-mail: [email protected]

Abstract. The illuminance responsivity dependencies on spectral powerdistributions �SPDs� of different types of light sources are studied. In thiswork we used three types of calibrated photometers, one of which washome-made and two were commercial photometers. A monochromator-based facility was used to scan SPDs of light sources. The dependen-cies of spectral mismatch correction factors F�St ,Ss� and the illuminanceresponsivities of photometers versus the SPDs of tungsten-filament in-candescent, fluorescent, high-pressure sodium, and metal-halide lightsources and white/colored light-emitting diodes are presented through-out this work. © 2007 Society of Photo-Optical InstrumentationEngineers. �DOI: 10.1117/1.2786888�

Subject terms: photometer head; illuminance responsivity; correlated colortemperature; spectral power distribution; incandescent lamp; fluorescentilluminants; high-pressure illuminants; light-emitting diodes.

Paper 060778R received Oct. 6, 2006; revised manuscript received Mar. 6, 2007;accepted for publication Apr. 13, 2007; published online Sep. 26, 2007.

Introduction

ifferent measurement methods and standards are used toealize photometric units. All of these methods are achievedia source-based or detector-based standards.1–7 By com-aring two methods, detector-based standards are preferredy the national metrology institutes �NMIs� in photometricealizations because they have the best reproducibility, re-eatability, and transportation flexibility. Photometric de-ectors �photometers� are divided into three main groups:tandard photometers, radiometers with appropriate filters,nd spectrophotometers. A V��-corrected or a��-corrected plus flat diffuser type of photometer is used

s a standard photometer. A photometer with a��-corrected filter is normally employed with a standard

ncandescent lamp placed on the optical axis of the pho-ometer at a sufficient distance to provide normal incidentight with a small divergence angle. V��-corrected typesf photometers without a diffuser are suitable for the lumi-ous intensity, retroreflection, and goniophotometer-baseduminous flux measurements.3,5,8,9 V��-corrected types ofhotometers with a diffuser are more subject to stray lightue to a large acceptance angle, but less subject to errorsor a large-size lamp at shorter distances. Generally,iffuser-type photometers are compatible for use in the il-uminance, luminance, and integrating sphere-based lumi-ous flux realizations.10–12

Spectrophotometers with a scanning grating and a detec-or combination or a constant grating and an array diodeombination are alternative devices for photometric mea-urements. Light sources are scanned between the visible

091-3286/2007/$25.00 © 2007 SPIE

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range, and photometric quantities �Xv� are defined in rela-tion to the corresponding radiometric quantity �Xe� by theequation

Xv = Km��

Xe��V��d� , �1�

where Km is the maximum spectral luminous efficiency forphotopic vision �683 lm/W� that relates radiometric quan-tities to photometric quantities, and V�� is the spectralluminous efficiency function, which is adopted by theCommission Internationale de l’Eclarge �CIE� as an aver-age action spectrum for the visual response of the humaneye. In the spectrophotometric method, errors coming fromthe CIE-V�� matching are eliminated because the standardCIE-V�� function is used to separate the photometricrange from the full measured radiometric spectrum.

To measure photometric quantities with a photometer ora radiometer, the device’s illuminance responsivity shouldbe precisely calibrated and the selected device must have arelative spectral responsivity matched to CIE-V��. Match-ing the spectral response of photometers to the V�� func-tion is the most important criterion of photometers. Thus,photometers are characterized for spectral mismatch to theCIE-V�� function by the calculation error factor f l�.

13

The luminous intensity is a quantity that describes thephotometric output of a light source while the illuminanceresponsivity is used to describe a photometer. To preciselycalculate the photometric quantity, the spectral responsivityof the photometer and the distribution temperature of thelight source should be known. Photometers are generallycalibrated against CIE Illuminant A �2856 K Plankian ra-diation�. An error occurs when a photometer measures a
light source that has a spectral power distribution �SPD�
September 2007/Vol. 46�9�1

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ifferent from the calibrated source. If the photometer’selative spectral responsivity and the spectral distributionsf the test and standard light sources are known, the spec-ral error can be corrected by the spectral mismatch correc-ion factor F�St ,Ss� as given by14

�St,Ss� =

��

St�� · V��d� · ��

Ss�� · srel��d�

��

St�� · srel��d� · ��

Ss�� · V��d�

, �2�

here St�� and Ss�� are the SPDs of the test and standardight sources, and srel�� is the relative spectral responsivityf a photometer. The photometer signal is multiplied by thisactor to eliminate spectral mismatch errors.

From the photometric point of view, there is an alterna-ive equation to calculate the spectral mismatch correctionactor of a photometer for an incandescent light source15:

�T� = � T

TA�m

, �3�

A is the color temperature of the standard Illuminant Aype light source �Plankian radiator operated at 2856elvin�, where m is the mismatch index, and T is the cor-

elated color temperature �CCT� of the source. The tungstenlament light source is operated at two different CCTs �T1nd T2� and the mismatch index is calculated according tohe following equation:

= log� I2�T2�I1�T1�

·y1�T1�y2�T2�

�� log�T2

T1� , �4�

here I1�T1� and I2�T2� are luminous intensities, and y1�T1�nd y2�T2� are photocurrents generated at the output of thehotometer obtained at temperatures T1 and T2.

This study presents illuminance responsivity variationsf a home-made photometer �a trap-detector based radiom-

Fig. 1 �a� Normalized relative spectral responsthe CIE-V�� functions.

ter� and two commercial photometers versus the SPDs of



different light sources. Variations of illuminance respon-sivities that depend on tungsten-based incandescent lamps,fluorescent and high-pressure illuminants, and differentlight-emitting diodes �LEDs� are introduced in Sec. 3.

2 Photometers Used in ExperimentsThe first photometer head is a temperature-controlled,V��-filtered photometer made by the National MetrologyInstitute of Turkey �UME� �model no. FR 25.0-1�. The ba-sic components of the photometer head, which is describedin Ref. 2, are a black, anodized, thin bimetal aperture witha 0.1-cm2 area; a PRC Krochmann-manufacturedV��-correction filter; and a trap detector �threeHamamatsu S1337-11 series photodiodes in a reflection-type trap configuration�. A circular thermoelectric Peltierelement and a Pt-100 temperature sensor are located in thephotometer housing to adjust and monitor the housing tem-perature. The photocurrent generated at the output of thephotometer is measured via a transimpedance amplifier�Lab Kinetics, Ltd., SP-042� and a digital multimeter com-bination �HP 3458 A�. The temperature of the photometerhousing was adjusted to 25.0°C±0.1°C. The second andthird photometers are temperature-stabilized photometerheads manufactured by PRC Krochmann �model no.TH15BA� and LMT Lichtmesstechnik GmbH �model no.P30SCT�. The PRC Krochmann-manufactured photometerhead has an aperture 10 mm in diameter and aV��-correction filter assembled in a cylindrical housing.The temperature of the housing is thermostatically stabi-lized at 35.0°C±0.1°C. The LMT LichtmesstechnikGmbH-manufactured photometer head has an aperture30 mm in diameter, colored glass filters, and a diffuser atthe entrance. The temperature of the housing is thermostati-cally stabilized at 25.0°C±0.1°C. The spectral mismatcherror factor of the photometer heads are f1�=1.5%, f1�=1.4%, and f1�=0.5%, respectively.

The relative spectral responsivity curves of the photom-eter heads and the differences between their CIE-V��

of photometer heads. �b� Differences between
ivities
functions are shown in Figs. 1�a� and 1�b�. As shown in



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ig. 1�b�, differences between the CIE-V�� functions andhe relative spectral responsivities of the photometer headsanufactured by UME and PRC Krochmann are similar.ajor variations are observed over wavelength ranges from

95 to 535 nm. The maximum variation from theIE-V�� function in the wavelength range is an order of2.3% �at 500 nm� for both photometer heads. Differences

rom 380 to 495 nm and from 535 to 780 nm fluctuateithin ±1.0%. The variation of the relative spectral respon-

ivity of the photometer head manufactured by LMTichtmesstechnik GmbH from the CIE-V�� function isbserved within ±1.1% �the maximum variation is at25 nm�.

Experiments and Resultsour different types of light sources are used in the experi-ents to determine dependences of illuminance responsivi-

ies versus SPDs. The groups of sources are based onungsten-filament incandescent lamps, fluorescent illumi-ants, high-pressure sodium and metal-halide illuminants,nd various LEDs.

.1 Relations Between Illuminance Responsivitiesof Photometer Heads and SPDs of Tungsten-Filament Incandescent Sources

wo types of lamps—the Osram Wi41/G �typicalA/180 W� and the Sylvania 1000-W quartz-tungsten

alogen lamp �ANSI designation, free electron laser lamps�typical 8.1 A/1000 W�—were used as the tungsten-lament lamps in the measurements. The Osram Wi41/G

amp was a gas-filled incandescent lamp having a reverse-onical shaped bulb. The Sylvania 1000-W lamp had aoiled-coil filament, mechanically clamped at both endsith no middle support. The SPDs of these lamps wereearly the same as the blackbody distribution. Therefore, itas not necessary to correct the illuminance responsivity ofphotometer at 2856 K by the spectral mismatch correc-

Table 1 Dependencies of the F�SsSt� factors anversus the CCTs of incandescent light sources.

CCT�K�

F�StSs� factor

FR 25.0-1 TH15BA P3

2000 1.0009 1.0005 1.

2200 1.0007 1.0004 1.

2400 1.0004 1.0003 1.

2600 1.0002 1.0002 1.

2800 1.0000 1.0000 1.

2856 1.0000 1.0000 1.

2900 0.9999 0.9999 0.

3200 0.9997 0.9997 0.

ion factor because F�St ,Ss� was equal to unity.



To change the CCT of the lamps, the applied current wasvaried in the experiments. The CCT of the Osram Wi41/Gextended to �2900 K, whereas the CCT of the Sylvanialamp extended up to �3200 K. The dependences of thespectral mismatch correction factors of the photometerheads on the SPDs of the lamps, and the influence of thesevariations on illuminance responsivities, were characterizedusing a double-monochromator-based measurement facility.Since the measurement system has been described in detailin earlier publications,1,16 only a brief overview of the setupis provided here. The measurement facility was based onthe Bentham Instruments, Ltd.-manufactured double-monochromator �DTMc300�, which had a wavelength re-peatability of 0.01 nm. The incandescent light sources weresequentially focused onto the entrance slit of the monochro-mator. A PTN 150-20 type of Heinzinger dc power supplywas used to operate the lamps at a constant-current mode.The photometer heads were held on a carriage placed at theoutput of the monochromator and translated via the com-puter control. The carriage also carried the reference trapdetector17 used to measure the SPDs of both the OsramWi41/G and the Sylvania light sources. Compensations forchanges in both light sources during the experiment weremade by using the signal from the monitor detector, de-scribed in Ref. 16. The SPD results were used to calculatethe spectral mismatch correction factors F�StSs� over therange 2000–3200 K with steps of 200 K according to Eq.�2�, and to determine the influences of the F�StSs� factorson the illuminance responsivities of the photometer heads�Table 1�.

The normalized SPD curves of sources having CCTs of2000 K, 2400 K, 2856 K, and 3200 K on the visible re-gion, and the variations in the F�StSs� factors of the pho-tometer heads versus the CCTs of tungsten-based incandes-cent sources, are shown in Figs. 2�a� and 2�b�. It wasobserved that the F�StSs� factors for all the photometerheads had approximately the same behavior �Fig. 2�b�.

illuminance responsivities of photometer heads

Influence on the illuminanceresponsivity, �RV �%�

FR 25.0-1 TH15BA P30SCT

0.09 0.05 0.09

0.07 0.04 0.06

0.04 0.03 0.04

0.02 0.02 0.02

0.00 0.00 0.00

0.00 0.00 0.00

−0.01 −0.01 −0.01

−0.03 −0.03 −0.02

d the

0SCT

0009

0006

0004

0002

0000

0000

9999

9998

Table 1 demonstrates that the F�StSs� factor of the UME-



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ade photometer head �FR 25.0-1� varied from 1.0009 �at000 K� to 0.9997 �at 3200 K�. The variation of the F�StSs�actor of the FR 25.0-1 resulted in the illuminance respon-ivity of the photometer head within an order of 0.09%elow 2856 K �at 2000 K� and −0.03% above 2856 K �at200 K�. The contributions of the F�StSs� factors to thelluminance responsivities of the PRC-made �TH15BA� andhe LMT-made �P30SCT� photometer heads at the sameCTs varied from 0.05 to −0.03% at 2000 K and 3200 K

or the TH15BA, respectively, and from 0.09 to −0.02% forhe P30SCT, respectively �Table 1�.

The ratio of the second term on the right side of Eq. �2�,Ss��srel��d� /Ss��V��d��, is constant for each typef light source and equal to 1.0030 �the FR 25.0-1�, 1.0000the TH15BA�, and 1.0007 �the P30SCT�. The multiplierSt��V��d�, the first term on the right side of Eq. �2�,xhibits the same behavior for all photometer heads. Theum of the multiplier increases due to the CCT of the lamp3.33 at 2000 K and 11.56 at 3200 K�. The multiplierSt��srel��d� plays an active role in the calculation of the

Fig. 2 Characterization results for incandescentthe F�StSs� factors versus CCTs.

Fig. 3 �a� Variations of Ss��srel��S ��V��d� /S ��s ��d� ratios.
t t rel


F�StSs� factor. The variations inSs��srel��d� /St��srel��d� of each photometer headfor the CCT range from 2000 to 3200 K are depicted inFig. 3�a�. Figure 3�a� shows that the variations of the pho-tometer heads ranging from 2600 to 3200 K were less than0.005% and varied more below 2600 K �0.1% at 2000 K�.The experimental light sources having CCTs below 2600 Khad poor SPDs compared with those above 2600 K �Fig.2�a�; therefore, the influence of the changes on the relativeresponsivity of the photometer heads �Fig. 1�b� was moreeffective for the SPDs below 2600 K.

3.2 Relations Between Illuminance Responsivitiesof Photometer Heads and SPDs of Fluorescentand High-Pressure Sources

Fluorescent and high-pressure illuminants have more en-ergy outputs in the 300- to 400-nm wavelength range, overwhich tungsten-based incandescent lamps do not have a

. �a� SPD curves for four CCTs. �b� Variations of

t��srel��d� ratios. �b� Variations of

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Table 2 Dependencies of the F�SsSt� factors and the illuminance responsivities of photometer headsversus the CCTs of fluorescent and high-pressure illuminants.

CIEilluminants

CCT�K�

F�StSs� factorInfluence on the illuminance

responsivity, �RV �%�

FR 25.0-1 TH15BA P30SCT FR 25.0-1 TH15BA P30SCT

FL4 2940 1.0009 1.0016 1.0003 0.09 0.16 0.03

FL3 3450 1.0005 1.0011 0.9999 0.05 0.11 −0.01

FL6 4150 1.0000 1.0005 0.9996 0.00 0.05 −0.04

FL2 4230 1.0000 1.0003 0.9996 0.00 0.03 −0.04

FL5 6350 0.9992 0.9991 0.9989 −0.08 −0.09 −0.11

FL1 6430 0.9992 0.9990 0.9989 −0.08 −0.10 −0.11

FL9 4150 0.9998 1.0000 0.9995 −0.02 0.00 −0.05

FL8 5000 0.9994 0.9993 0.9992 −0.06 −0.07 −0.08

FL7 6500 0.9992 0.9988 0.9989 −0.08 −0.12 −0.11

FL12 3000 1.0033 1.0034 1.0018 0.33 0.34 0.18

FL11 4000 1.0031 1.0030 1.0014 0.31 0.30 0.14

FL10 5000 1.0028 1.0026 1.0010 0.28 0.26 0.10

FL3.1 2932 1.0008 1.0016 1.0002 0.08 0.16 0.02

FL3.2 3965 1.0000 1.0004 0.9996 0.00 0.04 −0.04

FL3.3 6280 0.9991 0.9991 0.9989 −0.09 −0.09 −0.11

FL3.4 2904 1.0002 1.0010 0.9999 0.02 0.10 −0.01

FL3.5 4086 0.9998 0.9999 0.9995 −0.02 −0.01 −0.05

FL3.6 4894 0.9994 0.9993 0.9992 −0.06 −0.07 −0.08

FL3.7 2979 1.0030 1.0031 1.0015 0.30 0.31 0.15

FL3.8 4006 1.0027 1.0028 1.0011 0.27 0.28 0.11

FL3.9 4853 1.0028 1.0027 1.0010 0.28 0.27 0.10

FL3.10 5000 1.0025 1.0021 1.0009 0.25 0.21 0.09

FL3.11 5854 1.0027 1.0024 1.0008 0.27 0.24 0.08

FL3.12 2984 1.0005 1.0009 1.0001 0.05 0.09 0.01

FL3.13 3896 1.0001 1.0000 0.9997 0.01 0.00 −0.03

FL3.14 5045 0.9995 0.9991 0.9993 −0.05 −0.09 −0.07

HP1 1959 0.9989 0.9993 0.9998 −0.11 −0.07 −0.02

HP2 2506 1.0046 1.0049 1.0027 0.46 0.49 0.27

HP3 3144 0.9985 0.9989 0.9990 −0.15 −0.11 −0.10

HP4 4002 0.9972 0.9975 0.9981 −0.28 −0.25 −0.19

HP5 4039 0.9982 0.9982 0.9988 −0.18 −0.18 −0.12

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ignificant emission in the UV.18 Therefore, fluorescent origh-pressure illuminants are preferable sources, especiallyn colorimetric measurements.

In comparison with incandescent lamps, fluorescent illu-inants have some advantages. Fluorescent illuminants areore efficient than incandescent lightbulbs in terms of an

quivalent luminance. A large portion of the consumed en-rgy is converted to usable light and less is converted toeat, whereas an incandescent lamp may convert only 10%f its power input to visible light. However, the main dis-dvantage of fluorescent or high-pressure illuminants is thathey require a ballast to stabilize the lamp and provide thenitial striking voltage required to start the arc discharge.19

The CIE-standardized six groups of illuminants, repre-enting typical fluorescent lamps, were used to determinelluminance responsivity dependence.20 These include stan-ard fluorescent illuminants �FL1 to FL6�, broadband fluo-escent illuminants �FL7 to FL9�, narrowband fluorescentlluminants �FL10 to FL12�, standard fluorescent halophos-hate illuminants �FL3.1 to FL3.3�, DeLuxe-type fluores-

Fig. 4 Normalized SPD curves of fl

Fig. 5 Normalized SPD curves of high-pre
wavelength.


cent illuminants �FL3.4 to FL3.6�, three-band fluorescentilluminants �FL3.7 to FL3.11�, and multiband fluorescentilluminants �FL3.12 to FL3.14�. A standard high-pressuresodium illuminant �HP1�, a color-enhanced high-pressuresodium illuminant �HP2�, and three types of high-pressuremetal-halide illuminants �HP3-5� standardized by CIE werealso used. These illuminants cover the CCT range from�1950 to �6500 K. The SPDs of these illuminants differfrom the distribution of the Plankian radiator.

The SPD values for each illuminant tabulated in Ref. 20were normalized to unity at their maximum values, and theF�StSs� factors and the variations of the illuminance respon-sivities of the photometer heads were calculated �Table 2�.

The normalized SPD curves of a standard fluorescent�FL5�, a broadband fluorescent �FL9�, a narrowband fluo-rescent �FL12�, a standard fluorescent halophosphate�FL3.1�, a DeLuxe-type fluorescent �FL3.4�, and a multi-band fluorescent �FL3.12� illuminant are presented as ex-amples from their groups in Fig. 4. Figure 5 demonstrates

ent illuminants versus wavelength.

sodium and metal-halide illuminants versus
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he normalized SPD curves of the standard and color-nhanced high-pressure sodium illuminants �H1 and H2�nd the metal-halide illuminants �HP5�. Wien’s displace-ent law is not generated for fluorescent illuminants be-

ause they are not thermal sources like incandescent lamps.he SPDs of fluorescent sources are more complicatedompared to those of incandescent lamps, because power-gainst-wavelength graphs for their light outputs showany sharp peaks, not just one smooth curve. Fluorescent

ources have critical sharp peaks at 405-nm, 436-nm, and46-nm wavelengths, which originate from the excitedercury vapor in tubes. The difference between the SPDs

f each type of fluorescent illuminant and a standard sourcea tungsten filament light source operated at 2856 K� is theargest in the shorter wavelengths because the standardource has insufficient spectrum at 2856 K.

Table 2 shows that the maximum variation of the F�StSs�actor was generally observed for those illuminants that hadhe lowest CCT in their group. It was also observed that the

Fig. 6 �a� Variations of F�StSs� factors. �b� Valrescent illuminants.

Fig. 7 �a� Variations of F�StSs� factors. �b� V
fluorescent illuminants.


SPD values of the fluorescent illuminants’ wavelengthranges extended from 380- to 550-nm increases, dependingon the incremental portion of the illuminant’s CCT. Thecritical wavelength for the SPDs was 550 nm, because theilluminant with the lowest SPD under 550 nm pushed thehigher SPD beyond 550 nm. The inverse profile was ob-tained just above 550 nm for SPDs. The F�StSs� factors ofthe photometer heads were influenced more by use of boththe narrowband �FL10 to FL12� and the three-band fluores-cent illuminants �FL3.7 to FL3.11�. Illuminance responsivi-ties varied within an order of 0.3% for the FR 25.0-1 andthe TH15BA photometer heads for both illuminants statedabove, and less than 0.2% for the P30SCT photometerhead.

Figures 6 and 7 demonstrate the variations of the F�StSs�factors of the photometer heads and theSt��V��d� /St��srel��d� ratios for the standard fluo-rescent illuminants. Figure 6�b� shows that by increasing

St��V��d� /St��srel��d� for standard fluo-

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he CCT from 2940 K �FL4� to 6430 K �FL1�, theSt��V��d� /St��srel��d� ratios varied from 0.9979 to.9962 �for the FR 25.0-1�, from 1.0016 to 0.9990 �for theH15BA�, and from 0.9995 to 0.9982 �for the P30SCT�.he same variation characteristics were observed for the�StSs� factors of photometer heads �Fig. 6�a�. The sum of

he multiplier St��V��d� changed from 9.67 to 6.71.ifferences between multipliers St��srel��d� andSt��V��d� varied from 0.02 to 0.03, from −0.02 to 0.01,nd from 0.005 to 0.01 for the FR 25.0-1, the TH15BA, andhe P30SCT, respectively.

Figure 7�b� shows that by increasing the CCT from979 K �FL3.7� to 5854 K �FL3.11�, theSt��V��d� /St��srel��d� ratios varied from 1.0000 to.9997 �for the FR 25.0-1�, from 1.0031 to 1.0024 �for theH15BA�, and from 1.0008 to 1.0000 �for the P30SCT�.he sum of the multiplier St��V��d� was less sensitive

o the CCTs of illuminants and fluctuated around 3.5±0.2.ifferences between multipliers St��srel��d� andSt��V��d� at all CCTs was less than −0.01.

Figure 8�b� shows that by increasing the CCT from959 K �H1� to 4039 K �H5�, theSt��V��d� /St��srel��d� ratios varied from 0.9959H1� to 1.0016 �H2�, 0.9955 �H3�, 0.9942 �H4�, and 0.9952

Table 3 Dependencies of the F�SsSt� factors and the illuminanc

ModelCCT�K�

F�StSs� factor

FR 25.0-1 TH15BA

MWGC 4165 1.0007 1.0017

MW1D 5759 0.9997 1.0008

LW6C 7411 0.9992 1.0004

Fig. 8 �a� Variations of F�StSs� factors. �b� Valilluminants.



�H5� for the FR 25.0-1. The variations of the above ratiosfor the TH15BA and the P30SCT photometer heads, re-spectively, were 0.9993 and 0.9990, 1.0049 and 1.0020,0.9989 and 0.9983, 0.9975 and 0.9974, and 0.9982 and0.9980. The sum of the multiplier St��V��d� changedfrom 4.37 to 11.11. The differences between multipliersSt��srel��d� and St��V��d� varied from 0.02 to 0.05,from 0.003 to 0.02, and from 0.004 to 0.02 for the FR25.0-1, the TH15BA, and the P30SCT, respectively. Nega-tive differences for both of the multipliers were observedonly for the color-enhanced illuminant �−0.01, −0.04, and−0.02�.

3.3 Relations Between Illuminance Responsivitiesof Photometer Heads and SPDs of White andColored LEDs

An LED is a solid-state device that has an extremely longlife span—typically 10 years, twice as long as the best fluo-rescent bulbs, and 20 times longer than the best incandes-cent bulbs. These solid-state devices have no moving parts,no fragile glass environments, no mercury, no toxic gasses,and no filament. They also are much more efficient and aremore mechanically robust than incandescent lightbulbs andfluorescent tubes.21

onsivities of photometer heads versus the CCTs of white LEDs.

Influence on the illuminanceresponsivity,

�RV �%�

30SCT FR 25.0-1 TH15BA P30SCT

1.0003 0.07 0.17 0.03

0.9994 −0.03 0.08 −0.06

0.9992 −0.08 0.04 −0.08

St��V��d� /St��srel��d� for high-pressure

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In recent years, white and colored LEDs have been usedore as informative indicators in various types of embed-

ed systems, in transmitting digital information, and in il-umination applications. It is also known that due to thetability and modern features of LEDs, they are preferredor use in photometric and spectrophotometricpplications.22,23

To determine dependencies of the illuminance respon-ivities of photometer heads versus the CCTs of whiteEDs and color features of colored LEDs, the temperature-tabilized high-power Luxeon Star-type LEDs �manufac-ured by Lumileds Lighting, LLC� were used. Each LEDonsists of a Luxeon emitter mounted to a hexagonal alu-inum submount. The white LEDs have batwing �wide-

ngle radiation pattern� and Lambertian �flat radiation pat-ern� radiation patterns, whereas the colored LEDs haveambertian patterns.

Each LED was operated using a PTN 150-20 serieseinzinger dc power supply. The SPD of each LED was

Table 4 Dependencies of the F�SsSt� factors and the illum

ModelLXHL Color

F�StSs� facto

FR 25.0-1 TH15BA

LR5C Royal blue 1.0461 1.0175

MB1D Blue 1.0209 0.9961

ME1D Cyan 0.9897 0.9936

MM1D Green 0.9925 0.9964

ML1D Amber 0.9969 0.9969

MH1D Red-orange 1.0166 1.0163

MD1D Red 1.0148 1.0129

Fig. 9 �a� Normalized SPD curves of white LE
CCTs.


measured using a double-monochromator-based facility.The LEDs were separately attached to the input opening ofan integrating sphere, and the output opening of the sphere�with a diffuser� was attached to the input of the monochro-mator. The bandpass of the monochromator and the mea-surement steps were aligned to 5 nm, and the F�StSs� fac-tors were calculated by scanning each LED between 380and 780 nm. The measurement results for the white andcolored LEDs are shown in Tables 3 and 4.

White LEDs are composed of an InGaN chip coatedwith a phosphor composition. In Fig. 9�a�, the same phos-phor additive was used for the LXHLLW6C �7411 K� andLXHLMW1D �5759 K� types of LEDs, while a differentadditive was used for the LXHLMWEC �4165 K�. Themeasurements show that the influences of the F�StSs� fac-tors on the illuminance responsivities of the photometerheads were within ±0.1% for the FR 25.0-1, from 0.2% �at4165 K� to 0.04% �at 7411 K� for the TH15BA, and from

e responsivities of photometer heads versus LED colors.

Influence on the illuminanceresponsivity,

�RV �%�

P30SCT FR 25.0-1 TH15BA P30SCT

1.0201 4.61 1.75 2.01

1.0075 2.09 −0.39 0.75

0.9937 −1.03 −0.64 −0.63

0.9952 −0.75 −0.36 −0.48

0.9986 −0.31 −0.31 −0.14

1.0109 1.66 1.63 1.09

1.0094 1.48 1.29 0.94

Values of St��V��d� /St��srel��d� versus

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.03% to −0.08% for the P30SCT �see Table 3�. Figure 9�b�hows that by increasing the CCT from 4165 to 7411 K,he St��V��d� /St��srel��d� ratios varied from 0.9977o 0.9967 and 0.9962 for the FR 25.0-1. The variations ofhe St��V��d� /St��srel��d� ratios for the TH15BAnd P30SCT photometer heads, respectively, were 1.0017nd 0.9996, 1.0008 and 0.9987, and 1.0004 and 0.9984.he sums of the multiplier St��V��d� were 13.94,7.13, and 17.05 at 4165 K, 5759 K, and 7411 K, respec-ively. The differences between multipliers St��srel��d�nd St��V��d� varied from 0.03 to 0.06, from −0.02 to0.01, and from 0.01 to 0.03 for the FR 25.0-1, theH15BA, and the P30SCT, respectively.

The illuminance responsivities of the photometer headsere more influenced by the colored LEDs. The normal-

zed SPD curves of the colored LEDs are demonstrated inig. 10.

The basic chip used for the royal-blue �LXHL-LR5C�,he blue �LXHL-MB1D�, the cyan �LXHL-ME1D�, and thereen �LXHL-MM1D� LEDs is InGaN, whereas anlInGaP chip is used for the amber �LXHL-ML1D�, the

Fig. 10 Normalized SPD curve

Fig. 11 �a� Variations of F�S S � factors. �b� Val
t s
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red-orange �LXHL-MH1D�, and the red �LXHL-MD1D�LEDs. All the LEDs consist of Luxeon emitters mounted tohexagonal aluminum submounts. The LXHL-LR5C royalblue is part of the world’s brightest LEDs, with power�700 mW at 700 mA� and superb lumen maintenance thatfar exceeds other standard and high-flux LEDs. The maxi-mum continuous current for other LEDs is 350 mA. Unlikewhite LEDs, colored LEDs emit incoherent narrow-spectrum light and have narrowband SPDs. As shown inFig. 10, the dominant wavelengths of the LEDs were460 nm �royal blue�, 470 nm �blue�, 515 nm �cyan�,530 nm �green�, 595 nm �amber�, 625 nm �red-orange�,and 640 nm �red�. Full widths at half-maximums �FWHMs�of the LEDs were 20 nm �amber�, 25 nm �royalblue, red-orange, and red�, 30 nm �blue and cyan� and 35 nm�green�.

Figure 11�b� shows that theSt��V��d� /St��srel��d� ratios for the colored LEDsvaried the most for the royal-blue LED �1.043 for the FR25.0-1, 1.018 for the TH15BA, and 1.019 for the P30SCT�.The reason for this high variation is that the royal-blue

lored LEDs versus wavelength.

S ��V��d� /S ��s ��d� for colored LEDs.

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ED’s discrimination of the SPD is too high compared withhat of the standard illuminant. The same variation charac-eristics were observed for the F�StSs� factors of the pho-ometer heads �Fig. 11�a�. The influences of the F�StSs�actors on the illuminance responsivities of the photometereads for the royal-blue LED were 4.61% �for the FR 25.0-�, 1.75% �for the TH15BA�, and 2.01% �for the P30SCT�.he variations in the F�StSs� factors between the photom-ter heads for each of the LED colors are explained by theifferences in the relative spectral responsivities of the pho-ometer heads from the CIE-V�� function. The F�StSs�actor of a photometer head is influenced more by the LEDith the narrowest FWHM.The uncertainty budget to determine the F�St ,Ss� factor

or the incandescent and LED sources is given in Table 5.here are six main uncertainty components that directly

nfluence the calculation of the F�St ,Ss� factors. Theseomponents are the wavelength accuracy, the wavelengthepeatability and stray light of the monochromator, the un-ertainty in the SPD measurements, the current stability ofhe light source, and the relative spectral responsivity of thehotometer head. The combined uncertainty was takens the root of the sum of squares of the uncertaintyomponents.

The uncertainty of the photometer head in the relativeesponsivity determination was the most influential compo-ent on the total uncertainties: 0.06% for the FR-25.0-1,.08% for the TH15BA, and 0.10% for the P30SCT. Thencertainty in the relative responsivity was determined us-ng uncertainties from the responsivity of the reference trapetector, the power instability of the monochromatic beam,uctuations in the background radiation, the temperatureetting, noise levels in the transimpedance amplifier, etc.16

he other main uncertainty components used to determinehe F�St ,Ss� factors were the SPD measurements of lightources using the reference trap detector, and the current

Table 5 Uncertainty budget o

Source of uncertainty

Incande

FR 25.0-1 T

Optical power measurement 0.02

Wavelength scale 0.01

Wavelength repeatability 0.01

Stray light 0.01

Current stability 0.01

Relative spectral responsivity 0.06

Combined standard uncertainty 0.07

Expanded uncertainty �k=2� 0.13

etting stabilities of the light sources.



4 Conclusion

Dependencies of the illuminance responsivities of threetypes of photometer heads with the CCTs of different typesof light sources were studied. The characterized photometerheads were a UME-made trap detector-based photometerhead �the FR 25.0-1�, a PRC Krochmann-manufacturedphotometer head �the TH15BA�, and a LMT Licht-messtechnik GmbH-manufactured photometer head �theP30SCT�. A double-monochromator-based facility wasused to measure the SPDs of tungsten filament incandes-cent light sources and LEDs, and to calculate the F�StSs�factor of each photometer head with an expanded uncer-tainty of 0.2% �k=2�. The influences of the F�StSs� factorson the illuminance responsivities of photometer heads forthe fluorescent and high-pressure illuminants were deter-mined using spectral data for each type of illuminant tabu-lated by the CIE.

The measurements and calculations prove that the illu-minance responsivity values of the photometer heads cali-brated at 2856 K are affected more by the use of LED-typesources. The principal reason for this conclusion is that theLEDs have high SPDs in the restricted and narrow spectralbandwidth of the visible region. Moreover, some differ-ences between the relative spectral responsivities of thephotometer heads and the CIE-V�� function are observed,depending on wavelength, because the photometers areequipped with V��-corrected filters. Therefore, somevariations on the F�StSs� are obtained for each photometerhead. In particular, when using the royal-blue LED, theilluminance responsivity for the FR 25.0-1, the TH15BA,and the P30SCT changed from 4.6% to 1.8% and 2.0%,respectively. For the red-orange and red LEDs, the varia-tions on the illuminance responsivity are 1.5%, 1.3%, and0.9%. When using the white LEDs, the variation on theilluminance responsivity remains restricted within ±0.1%

�St ,Ss� factor determination.

�100� relative uncertainty�

source LED source

P30SCT FR 25.0-1 TH15BA P30SCT

0.02 0.04 0.04 0.04

0.01 0.01 0.01 0.01

0.01 0.01 0.01 0.01

0.01 0.01 0.01 0.01

0.01 0.03 0.03 0.03

0.10 0.06 0.08 0.10

0.10 0.08 0.10 0.11

0.21 0.16 0.19 0.23

f the F

scent

H15BA

0.02

0.01

0.01

0.01

0.01

0.08

0.08

0.17

�4000 to 7500 K� because white LEDs have SPDs on the



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hole visible region. The same variation was also observedor the incandescent light sources. A light source with aCT of 2000 K influences the illuminance responsivity of

he photometers an order of 0.1%.Among fluorescent and high-pressure illuminants, the

ight sources affecting illuminance responsivity are narrow-and and three-band fluorescent illuminants ��0.3% �. Theeason for the difference is that such illuminants havebrupt spectral slopes in the narrow spectral bandwidthuch as LEDs. High-pressure and color-enhanced illumi-ants, the SPD of which changes the wavelength rangeharply from 570 to 615 nm, have the highest SPD distri-ution of all the illuminants in the red region of the spec-rum and affect the illuminance responsivity the most�0.5% �.

eferences

1. F. Samedov and O. Bazkir, “Realization of photometric base unit ofCandela traceable to cryogenic radiometer at UME,” J. Eur. Appl.Phys. 30�3�, 205–213 �2005�.

2. F. Samedov, M. Durak, and O. Bazkır, “Filter-radiometer based real-ization of Candela and establishment of photometric scale at UME,”Opt. Lasers Eng. 43�11�, 1252–1256 �2005�.

3. Y. Ohno, “Improvement photometric standards and calibration proce-dures at NIST,” J. Res. Natl. Inst. Stand. Technol. 102, 323–331�1997�.

4. C. L. Cromer, G. Eppeldauer, J. E. Hardis, T. C. Larason, and A. C.Parr, “National Institute of Standards and Technology detector-basedphotometric scale,” Appl. Opt. 32, 2936–2948 �1993�.

5. J. Metzdorf, “Network and traceability of the radiometric and photo-metric standards at the PTB,” Metrologia 30, 403–408 �1993�.

6. L. P. Boivin, A. A. Gaertner, and D. S. Gignac, “Realization of thenew candela �1979� at NRC,” Metrologia 24, 139–152 �1987�.

7. P. Toivanen, P. Karha, F. Manoochehri, and E. Ikonen, “Realizationof the unit of luminous intensity at the HUT,” Metrologia 37, 131–140 �2000�.

8. F. Samedov, O. Celikel, and O. Bazkır, “Establishment of acomputer-controlled retroreflection measurement system at the Na-tional Metrology Institute of Turkey �UME�,” Rev. Sci. Instrum.76�9�, 096102 �2005�.

9. G. Sauter, “Goniophotometry: new calibration method and instru-
ment design,” Metrologia 32, 685–688 �1995/96�.


10. F. Sametoglu, “New traceability chains in photometry and radiometryat the National Metrology Institute of Turkey,” Opt. Lasers Eng.45�1�, 36–42 �2007�.

11. F. Samedov and M. Durak, “Realization of luminous flux unit oflumen at UME,” Opt. Appl. 34, 265–274 �2004�.

12. P. Toivanen, J. Hovila, P. Karha, and E. Ikonen, “Realizations of theunits of luminance and spectral radiance at the HUT,” Metrologia 37,527–530 �2000�.

13. CIE, The Basis of Physical Photometry, Publication No. 18.2 �1983�.14. Y. Ohno and A. E. Thompson, “Photometry—the CIE V�� function

and what can be learned from photometry,” in Measurements of Op-tical Radiation Hazards—A Reference Book Based on PresentationsGiven by Health and Safety Experts on Optical Radiation Hazards,Sep. 1–3, 1998, Gaithersburg, MD, ICNIRP 6/98, CIEx016-1998, pp.445–453 �1998�.

15. W. Erb and G. Sauter, “PTB network for realization and maintenanceof the candela,” Metrologia 34, 115–124 �1997�.

16. F. Sametoglu, “Establishment of illuminance scale at UME with anabsolutely calibrated radiometer,” Opt. Rev. 13�5�, 326–337 �2006�.

17. O. Bazkir and F. Samedov, “Characterization of silicon photodiodebased trap detectors and establishment of spectral responsivity scale,”Opt. Lasers Eng. 43, 131–141 �2005�.

18. G. Wyszecki, “Development of new CIE standard sources for colo-rimetry,” Die Farbe 19, 43–76 �1970�.

19. CIE, The Measurement of Luminous Flux, Publication No. 84 �1989�.20. CIE, Colorimetry, Publication No. 15.3 �2004�.21. E. Mills, “The specter of fuel-based lighting,” Science 308, 1263–

1264 �2005�.22. C. F. Jones and Y. Ohno, “Colorimetric accuracies and concerns in

spectroradiometry of LEDs,” in Proc. CIE Symposium ’99—75 Yearsof CIE Photometry, Budapest, Hungary, pp. 173–177 �1999�.

23. F. Samedov, M. Durak, and A. K. Turkoglu, “Photometric character-izations of light emitting diodes,” in Proc. 2nd Balkan Conference onLighting, Istanbul, Turkey, pp. 150–155 �2002�.

Ferhat Sametoglu graduated from thephysics department, Baku State University,Azerbaijan, in 1993. He worked at the Pho-toelectronic Institute of the Academy of Sci-ence of Azerbaijan from 1993 to 1998 andreceived his PhD degree there in 1998. Hehas been working in the Optics Laboratoryat the National Metrology Institute of Turkey�UME� since 1999 and headed the labora-tory from 2001 to 2006. He has been amember of the Optical Society of America

and SPIE since 2005. His main interest is optical metrology.



Documents

Relation between the illuminance responsivity of a photometer and the spectral power distribution of a source