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Research ArticleImpact of LED Color Temperatures on Perception Luminance inthe Interior Zone of a Tunnel considering Fog Transmittance

Lili Dong Enzhong Zhao Yang Chen Ge Qin and Wenhai Xu

School of Information Science and Technology Dalian Maritime University Dalian 116026 China

Correspondence should be addressed to Lili Dong dll_lili163com

Received 5 December 2019 Revised 1 February 2020 Accepted 6 February 2020 Published 24 April 2020

Academic Editor Valeria Vignali

Copyright copy 2020 Lili Dong et al )is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

LEDs are widely applied in highways and tunnels for their long life low light attenuation and being environment friendly inrecent years )e influence of correlated color temperature (CCT) of LED on lighting safety has attracted peoplersquos attention as thedemand increased In this paper a calculation model of perception luminance of human eye considering mesopic vision and fogconcentration was proposed )e influence of different CCTs on perception luminance of human eye under different levels of fogconcentration and luminance was calculated and analyzed)e CCTof LED employed in the interior zone of a tunnel was selectedbased on the highest perception luminance in mesopic vision Seven kinds of LEDs with different CCTs (3000ndash6500K) wereapplied in the experimental system with adjustable fog concentrations )e results showed that the main factors affecting visualperception are luminance and fog concentration Higher luminance or lower fog concentration provides drivers with higherperception luminance In contrast although CCT has a less effect on perception luminance LEDs with higher CCT (about 6500K)can provide higher perception luminance considering fog in mesopic vision )is paper provides technical support for tunnellighting and guaranteeing traffic safety

1 Introduction

Tunnel lighting is an important aspect of ensuring traffic andtransport safety in highway tunnel Many countries havelighting requirements for each section of the tunnel anddetermine whether the requirements are met based on themeasurements of the instrument [1ndash3] In China theGuidelines for Design of Lighting of Highway Tunnels JTGT D702-01mdash2014 (JTG) divided the tunnel into four parts(threshold zone transition zone interior zone and exitzone) with different luminance requirements )e lumi-nance of the entrance zone and exit zone is designed to behigher in order to reduce the influence of luminance dif-ference between the inside and the outside of the tunnel ontraffic safety in the daytime Taking advantage of the ad-aptation of the human eye to the dark the luminance of theinterior zone is designed to be minimal in order to saveenergy )e tunnel division in four parts can provide auniversal reference for the tunnel lighting design whileensuring the safety of driving to maximize energy saving

Based on the traffic volume and the designed speed theluminance requirement for interior zone is the lowest forabout 1 cdm2sim10 cdm2 [4] Due to the semienclosedstructure of the tunnel the particles emitted from motorvehicles and deposited dust can hover for a long time in theair by gravity and cause a foggy condition Both low lu-minance and fog conditions will pose a real threat to drivingsafely in the interior zone and as a result improving thevisual quality of drivers by studying tunnel lighting is ofsignificant importance

)e energy consumption of tunnel lighting is larger thanhalf of the total energy consumption of tunnel [5 6]Nowadays LEDs are widely applied in highways and tunnelsbecause of their long life low light attenuation and energysaving whose correlated color temperature (CCT) can covera common range of 3000Ksim6500K [7 8] When the color ofthe light emitted by the light source is close to the color of theradiation of the black body at a certain temperature thetemperature of the black body is called the correlated colortemperature of the light source Researchers have carried out

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 3971256 13 pageshttpsdoiorg10115520203971256

many studies on energy saving of tunnel lighting In 2011Gil-Martın [9] presented tension structures for tunnel tosave energy in the most energy requiring zone (the thresholdzone) and reduce the number of luminaries In 2015 Salata[10] presented that LEDs are suitable for the interior zonedue to their luminous efficiency )anks to their longerservice life they reduce maintenance expenses In 2018Cantisani [11] computed and compared the environmentalimpacts of two lighting systems LED and high-pressuresodium (HPS) in a twin-tube road tunnel He presented thatalthough LEDs cost more in terms of construction andinstallation than HPS they cost less to maintain later In2019 he calculated the energy savings from replacing HPSswith LEDs in Italyrsquos Greenlight project )e results showedthat the new lighting systems will reduce electricity con-sumption by up to 50 of the current values [12] Althoughenergy saving is an essential issue in tunnel lighting designsafety should also be taken into consideration

In the past few years our laboratory has providedlighting design for several tunnels of Heda highway in Jilinprovince of China and accumulated some practical engi-neering experience and problems to be improved )e de-partment of tunnel lighting design and management paysgreat attention to the selection of CCTof LED but there areno official guidelines for reference )erefore it is mean-ingful to explore the effect of CCT on human vision Lu-minance is the main influence factor of safety in tunnellighting Two main factors should be considered for safedriving in the interior zone of a tunnel considering fogcondition human eye perception and transmittance of LEDswith different CCTs in fog condition

)e luminance perceived by human eye is different whenthe ambient luminance and wavelength of light are differentHuman vision is divided into photopic vision scotopicvision and mesopic vision according to the visual phe-nomena caused by light of different wavelengths acting onvisual organs in different luminance ranges [13ndash15] Pho-toreceptor cells in the retina can be divided into two typescones and rods )e luminance range of photopic vision isabout above 3 cdm2 when cones play a major role In thiscase the human eye can distinguish the details and colors ofobjects )e luminance range of scotopic vision is aboutbelow 10minus3 cdm2 when rods play a major role In this casethe human eye can only distinguish light and dark and theability to distinguish details and colors of objects is greatlyreduced Most of the luminance of tunnel lighting belongs tothe range of mesopic vision when both types of cells worksimultaneously in a specific proportion )e mesopicspectral luminous efficiency function varies depending onthe luminance and the interaction between cones and rodsdiffers with luminance levels Several researches concernedwith mesopic vision have been carried out in recent years In2006 Viikari [16] and others measured the reaction time andcontrast threshold to evaluate mesopic visual performance indifferent spectral conditions In 2011 Li [17] and otherspresented that the higher CCT of LEDs have better visualeffects by calculating the mesopic equivalent illumination ofthe different sources In 2016 Huai [18] conducted a test oncolor discrimination and presented that the human eyersquos

ability to distinguish colors improves as CCT increases inmesopic condition In 2018 Du [19] studied the overallluminance performance and indicated that LEDs with highCCT have better luminance performance in lighting re-duction coefficient in threshold zone of tunnel All the abovestudies satisfied the mesopic visual characteristics undergeneral conditions As tunnels are prone to the phenomenonof low visibility it is necessary to consider the effect of fogwhen studying the mesopic vision in tunnel

)e value of CCT is determined by the spectrum of LED)e transmittance of light in fog is affected by the wave-length of light source)erefore it can be inferred that LEDswith different CCTs provide different visual perception infog Some researchers studied the relationship betweenmonochromatic lights and transmittance in fog In 2012Otas [20] and others presented an experimental investiga-tion of the characteristics of the propagation of light emittedby various colors in artificial fog with varying density )eexperiment showed that the light of shorter wavelengths(blue and green) is seen to be less attenuated by scatteringthan that of longer wavelengths In 2013 Zeng [21] andothers researched the penetration properties of LED lightsources in water fog and sea fog showing that the trans-mittance of yellow LEDwas the best followed by blue greenand red In 2016 Brandon [22] and others studied the at-tenuation characteristics of LEDs with six different wave-lengths in a controlled fog chamber )ey got the result thatthe red light has the least attenuation followed by yellow andgreen )e blue light had the worst performance Reaching aunified conclusion about the relationship between wave-length and transmittance from the above researches is hardHuai [18] studied the effect of three CCTs (1870K 2985K and5020K) on penetration properties in fog and presented thatlow-color-temperature (around 3000K) LEDs are moresuitable for street lighting by calculating the transmittanceMost studies of light transmittance are concerned withmonochromatic light not with CCT As a result we shouldconsider the influence of LED with different CCTs on boththe transmission and the mesopic spectral luminous effi-ciency function on tunnel lighting )e most sustainableluminaire in tunnel LED was studied and the impact ofCCT on perception luminance in the interior zone of thetunnel considering different levels of luminance and fogconcentrations was explored for traffic and transport safety)e calculation and experimental results showed that highluminance or low fog concentration could provide highperception luminance High CCTs (about 6500K) couldprovide higher visual clarity But the effect of CCT is rela-tively inferior to luminance and fog concentration )eseconclusions provide reference for tunnel lighting designguidelines for traffic safety energy saving and the selectionof CCTs

2 Theory of Perception Luminance

Considering fog conditions in tunnel the perception lu-minance of human eye is affected by the mesopic spectralluminous efficiency function the spectrum and luminanceof LED and the fog transmittance Human eye perception

2 Advances in Civil Engineering

luminance in mesopic vision considering transmittance oflight can be calculated by the following equations

Lf 1113946780

380kmVmes(λ)L

lowaste (λ)dλ (1)

Lp 1113946780

380683V(λ)L

lowaste (λ)dλ (2)

Llowaste (λ) Le(λ) middot T(λ) (3)

where Lf refers to the perception luminance of human eye inmesopic vision whose units of measurement is cdm2 kmrefers to maximum spectral light performance corre-sponding to mesopic vision luminance Vmes(λ) is themesopic spectral luminous efficiency function depends onLp Lelowast(λ) refers to spectral radiance distribution (SPD)under a certain concentration of fog Lp refers to the lu-minance of light through fog in photopic vision whose unitsof measurement is cdm2 V(λ) refers to the photopicspectral luminous efficiency function Le(λ) refers to SPDmeasured by spectral radiance meter under the absence offog and T(λ) refers to the transmittance of differentwavelength at a certain fog concentration

21 Le(λ) Le(λ) refers to the SPD measured by spectralradiance meter under the absence of fog Seven kinds ofLEDs with different CCTs applied in highway tunnel wereselected in the following experiment to analyze their SPDswhose CCTs are 3000K 3500K 4000K 4500K 5000K5700K and 6500K as shown in Figure 1

)e LEDs employed in highway tunnels are mainlysuperimposed by the blue light emitted by the GaN chip andthe yellow light excited by yttrium aluminum garnet (YAG)phosphor [23] )e SPDs of LED with different CCTs (Le(λ))shown in Figure 2 are measured by a spectrophotometercalled Konica-Minolta CS-2000 under the luminance of10 cdm2 )e characteristics of the spectrum are doublepeaks broad spectrum )e valley between the two peaks isclose to 480 nm

22 T(λ) T(λ) is defined as the transmittance of differentwavelengths under a certain fog concentration and is cal-culated by the ratio of illuminance with fog to illuminancewithout fog Transmittance can indicate the concentration offog and the two are negatively correlated To make the datamore reliable the transmittance of nine monochrome LEDswith different center wavelengths were measured under fivedifferent fog concentrations in a sealed fog chamber Fig-ure 3 shows the relative luminance intensity of ninemonochromatic LEDs )e range of central wavelength is420 nmsim660 nm

Figure 4 shows the schematic diagram of experimentalsetup Nine monochrome LEDs of the same model were putat one side of the fog chamber and the illuminometer wasput at the other side of the chamber)e following shows theexperimental procedure Firstly when there was no fog inthe chamber nine monochrome LEDs were adjusted to have

the same illuminance (40lx) measured by the illuminometerAll light sources were turned off except monochrome LEDwith a wavelength of 420 nm as a reference light sourceSecondly the fog generator released fog into the chamber)e concentration of fog can be maintained at a certain valueby observing the readings of illuminometer and controllingthe flow rate )e transmittance of the reference light source(T) was calculated to represent various concentration levels(T 20 40 60 80 and 100 in this experiment))irdly when the concentration of fog reached a stable anddemanded value the reference light source was turned offand the other eight monochrome LEDs were turned on byturns )e values of illuminance of eight monochrome LEDsin a certain concentration of fog were recorded and thevalues of transmittance were calculated by turns Ninemonochrome LEDs were placed in the same location )esame procedure was repeated 10 times to reduce the ex-perimental error

Figure 5 shows the average transmittance of 10 groupsincluding nine monochrome LEDs under five levels of fogconcentration It can be seen from Figure 5 that in the caseof different fog concentrations the tendencies of luminanceattenuation of the respective wavelengths are the same andthe main difference is the amplitude of the attenuation T(λ)can be obtained by interpolation based on the experimentalresult

23 KmVmes(λ) Km Vmes(λ) refers to the mesopic spectralluminous efficiency function It is generally considered thatthemesopic luminance is in the range of 10minus3 cdm2 to 10 cdm2 [14] while the luminance of tunnel lighting mostly fallswithin this range [4] )e human retina is composed ofcountless photoreceptor cells )ey are divided into conecells and rod cells according to their shape Unlike photopicvision and scotopic vision in which only one type of cellfunctions mesopic vision is activated by two types of cells atthe same time and the number of the two types of cells isdetermined by luminance [24 25] )erefore the mesopicspectral luminous efficiency function cannot represent therelative sensitivity of the human eye to different wavelengthsof light using a single spectral luminous efficiency curve It isnecessary to use a series of curves at different luminancelevels to describe the mesopic spectral luminous efficiencyfunction In 2010 the International Commission on Illu-mination [26] recommended four mesopic vision modelsbased on visual efficiencies USP model MOVE modelMES1 model and MES2 model

Figure 6 plots the difference curves between mesopicluminance and photopic luminance (LmesminusLp) which varywith the photopic luminance when SP values of LED are 1420 and 23 respectively It can be seen from Figure 6 thatthe mesopic luminance calculated by four different mesopicmodels under the same photopic luminance is differentMoreover the mesopic luminance calculated by the fourmesopic vision models is greater than the photopicluminance

)e upper luminance limit (06 cdm2) of the mesopicregion is too low for the USP model USP model limits the

Advances in Civil Engineering 3

applicability to achromatic tasks only )e chromatic tasksdominated in MOVE model But in real-tunnel situationssuch as driving through a tunnel both achromatic andchromatic tasks are involved and the achromatic tasks may

be slightly underweighted in the MOVE model [25]Comparing MES1 and MES2 models MES2 model has awider range of luminance which means that MES2 model ismore suitable for both color vision tasks and achromaticvision tasks and more suitable for the analysis model ofmesopic vision in the tunnel In MES2 model ifLmesge 50 cdm2 then m 1 if Lmesle 0005 cdm2 thenm 0 )at is to say if the MES2 model is adopted thephotopic luminance should be selected to be below 50 cdm2 Although the upper limit for the photopic luminance ofthe interior zone of the tunnel is 10 cdm2 considering thefog condition in tunnel the perceived luminance may belower than 5 cdm2 so it is reasonable to use MES2 model inthis research )e mesopic spectral luminous efficiencyfunction can be obtained through MES2 model )e fol-lowing are the calculation equations of MES2 model

km 683lm middot Wminus 1

Vmes(λ 555 nm) (4)

Vmes(λ) 683m2V(λ) + 1 minus m2( 1113857Vprime(λ)

m2 + 1 minus m2( 1113857Vprime λ0( 1113857 0lem2 le 1

(5)

m2n 03334 log Lmesn + 0767 0lem2n le 1 (6)

Lmesn m2nminus1 + 1 minus m2nminus11113872 1113873(SP)Vprime λ0( 1113857

m2nminus1 + 1 minus m2nminus11113872 1113873Vprime λ0( 1113857Lp (7)

a2 + b2SP

1113968

1113946 Vprime(λ)Le(λ)dλ

Vprime λ0( 1113857 1113946 V(λ)Le(λ)dλ (8)

3000K 3500K 4000K 4500K 5000K 5700K 6500K

Figure 1 Seven kinds of LEDs applied in tunnel with different CCTs

Abso

lute

spec

tral

pow

er d

istrib

utio

n(W

srlowast

m2 )

400 500 550 600 650 700 750450Wavelength (nm)

00000

00001

00002

00003

00004

00005

00006

00007

00008

00009

3000K3500K4000K4500K

5000K5700K6500K

Figure 2 Spectral power distribution of 7 LEDs with differentCCTs

400 450 500 550 600 650 700 750350Wavelength (nm)

00

02

04

06

08

10

Rela

tive l

umin

ous i

nten

sity

420nm450nm475nm505nm520nm

570nm595nm640nm660nm

Figure 3 Relative luminance intensity of nine monochromaticLEDs

Fog chamber

MonochromaticLED

Illuminometer

Fog generator

Figure 4 )e schematic diagram of experimental setup


where Vmes (λ 555 nm) is the value of Vmes(λ) at 555 nmm2 refers to the luminance adaptation factor Vprime(λ) refers tothe value of scotopic spectral sensitivity function Vprime(λ0)refers to the value of scotopic spectral sensitivity function atλ0 555 nm the value of which is 6831699 Lmes refers to themesopic luminance )e value ofm2 can be calculated basedon (6) and (7) by a sequence of interactions n refers to aniteration step )e value of SP refers to scotopic to photopicluminous flux ratios of light sources

)e calculation process of getting mesopic spectral lu-minous efficiency function is shown in Figure 7 Firstly the

value of SP is calculated by (8) according to the spectraldistribution of different light sources (Le(λ)) )e SP ratiosof the seven kinds of LEDs used in this study are shown inTable 1 Secondly Llowaste (λ) is calculated by Le(λ) and T(λ) Andthen the value of Lp can be calculated by (2) )irdlysubstituting SP and Lp into the calculation equations (6) and(7) the value of the parameterm2 can be obtained And thenKmVmes(λ) can be calculated by (4) and (5) )e spectralluminous efficiency curves of photopic scotopic andmesopic vision are shown in Figure 8 )e mesopic curvesare located between the photopic vision and scotopic visionFor spectral luminous efficiency curves of photopic mes-opic and scotopic vision the four luminance values in theupper left corner correspond to the mesopic luminance Forthe spectral luminous efficiency curves of the seven LEDs onthe right the value of photopic luminance is 1 cdm2 InFigure 8 mesopic curves do not have the same pattern as thecurves at the top right As the luminance decreases themesopic curves get closer to the scotopic vision and the peakof mesopic curves gets higher Under a certain luminancelevel LEDs with low CCTs provide higher luminous effi-ciency curves

24 Lf Lf refers to the perception luminance of human eyein mesopic vision and it is one of the main influencingfactors of visual quality According to formulas (1)sim(8) thecalculation process of Lf is shown in Figure 9 After mea-suring T(λ) and Llowaste (λ) Vmes(λ) can be plotted by (2)sim(8)and then Lf can be calculated by (1) and (3)

25 -e Calculation Results of Perception Luminance )eresults of the theoretical calculation results are shown inFigure 10)e values of each parameter are shown in Table 2considering the luminance in MES2 and various transmit-tances )e main research content of this paper is the dif-ference of CCT so discretization will not affect theexperimental results It can be seen from Figure 10 that Lf isgreatly affected by the luminance under absence of fog (L)and fog concentration and is less affected by the CCT )evalue of Lf increases as the luminance or transmittanceincreases Under a certain luminance and fog concentrationLEDs with higher CCT always provide higher Lf )e dif-ference of Lf provided by two adjacent CCTs is about 002 cdmminus2 which means that the influence of CCT on Lf is rela-tively small in the theoretical calculation and perhaps in areal tunnel the human eye can hardly perceive the differ-ences of CCTs However the calculation results are notcompletely consistent with the actual human eyes and it stillneeds experimental verification

3 Experiment

31 Experimental Setup As perception luminance cannot bedirectly measured by instruments this experiment indicatedthe perception luminance by judging the clarity levels of thetarget by human eye Visual clarity refers to the theory aboutthe target-background contrast )e contrast can be cal-culated by

Reference light

450 475 505 520 570 595 640 660 -- --420Wavelength (nm)

00

02

04

06

08

10

Tran

smitt

ance

1008060

4020

Figure 5 SPDs of nine monochromatic LEDs Error bars indicatestandard deviation

L mes

ndashLp (

cdm

2 )

2 4 6 8 100Photopic luminance (cdm2)

000

005

010

015

020

025

030

MOVE modelMES2 modelMES1 modelUSP model

SP = 14SP = 20SP = 23

Figure 6 Comparison of four mesopic photometry models withdifferent SP ratio


C Lb minus Lt

Lb

(9)

where C refers to the target-background contrast Lb refers tothe background luminance and Lt refers to the target lu-minance In this experiment the color of the target (visualchart) is black As a result C is mainly affected by theperception luminance of the background It can be con-cluded that the higher the perception luminance the higherthe visual clarity

Although experiments in real tunnel would be closer toactual driving condition some variables are hard to controlFor example the fog concentration and uniformity of each

experiment cannot be guaranteed as they change over timewhich will seriously affect the accuracy of experimentalresults )e fog chamber can produce stable fog and wasused to ensure the accuracy of data )e danger of driving ina tunnel is caused by the fact that the eyes do not perceiveobstacles in front in time which involves the theory abouttarget-background contrast and the main factor is per-ception luminance As a result it is reasonable to replace thetraffic model of real tunnel with the static simplified model

Figure 11 illustrates a schematic diagram of experimentalsetup Figure 12 shows the real experimental situation )efog chamber was made of wood and organic glass thevolume of which was 500times 500times 500mm2 )e interior ofthe chamber was painted black except the organic glass toavoid the diffuse reflection of light and designed to be sealedIt has been confirmed that the organic glass has little effecton spectral luminous efficiency or visual perception exceptreducing luminance Two sides of the chamber were made ofglass so that the light of LEDs placed on either side couldshine into the chamber Besides the side near the observerwas also partly made of glass for observing In order toreduce the experimental error two LEDs with differentCCTs were placed on both sides of the chamber and thelights were placed alternately like Figure 11(c) It has beenconfirmed through a preliminary experiment that such aplacement of lights does not affect the experiment A visualchart was attached on the side away from the observerBelow the visual chart was an illuminometer to measure theilluminance and calculate the transmittance)e E letter waspainted in black with a reflectance of 02 and the reflectanceof different wavelengths is the same In mesopic vision thecone cells do not play a major role so the human eyersquosresolution of color is greatly reduced In JTG there is adescription of the driverrsquos visual cognition of obstacles in thetunnel JTG specifies that the obstacle uses a small blacktarget with a reflection coefficient of 02 We designed thevisual acuity chart based on this rule

)e observer could just observe the visual chart throughthe glass )e fog generator (FOGGER A-1500) was putbehind the fog chamber and could produce stable anduniform fog )e walls around the chamber were paintedblack to prevent the influence of diffuse reflection on theexperiment and to simulate the dim environment in realtunnel )e distance between the subjects and the fogchamber is 1m

50 observers (25 females and 25 males) aged 24 to 56with normal color vision and normal binocular eyesightparticipated in this experiment We chose four luminance

T(λ)

Le(λ)

SP

Lelowast(λ) Lp m2 Vmes(λ) kmVmes(λ)(3)(2)

(7)(6) (5) (4)

Measured part Calculated part

(8)Iterative process

Figure 7 Calculation process

Table 1 )e SP value of seven light sources

CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)

Scotopic vision1cdm2

2cdm2

3cdm2

4cdm2

Photopic vision

Figure 8 Spectral luminous efficiency curves of photopic scotopicand mesopic vision of seven kinds of LEDs with different CCTs


levels (1 cdm2 2 cdm2 3 cdm2 and 4 cdm2) five trans-mittance levels (20 40 60 80 and 100) and sevenCCTs (3000K 3500K 4000K 4500K 5000K 5700K and6500K) totally 140 lighting conditions

32 Effects of Luminance and Fog Transmittance In de-signing this part of the experiment we have attempted torequest the subjects conduct the experiment under theconditions of seven CCTs However due to the

discretization of the visual chart when using LEDs withdifferent CCTs under the same luminance and fog con-centration the line where the smallest E could be seen clearlyand the subjects distinguishing the direction was almost thesame )e difference is only a matter of the degree of clarity)is phenomenon verifies the theoretical calculation resultsof perception luminance compared with CCT luminanceand fog concentration have a much greater impact on visualclarity It can be concluded that when considering the effectof LEDs on the perception luminance of the human eye in

Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)

kmVmes(λ)Lelowast(λ)

Lf

Figure 9 )e calculation process of Lf

Perc

eptio

n lu

min

ance

(cd

m2 )

40 60 80 10020Transmittance ()

3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40

Figure 10 )e calculation results of Lf

Table 2 )e values of each parameter

Luminance without fog (L) CCT Transmittance (T)1cdm2 2 cdm2 3 cdm2 4 cdm2 3000K 3500K 4000K 4500K 5000K 5700K 6500K 20 40 60 80 100


fog conditions which CCT to use does not make muchdifference As a result it is appropriate to select only oneCCT in this part of the experiment LEDs with 6500K wereused as the light source

In Step 1 LEDs with CCT of 6500K were adjusted to ademanded illuminance level under the absence of fogAccording to the average luminance-average illuminationconversion coefficient given by JTG (usually taken as 10lx(cdmiddotmminus2)) [4] the values of illuminance (Li) were selected as10lx 20lx 30lx and 40lx

In Step 2 the fog generator released fog into thechamber )e concentration of fog could be adjusted bycontrolling the flow of the fog generator )e illuminometer

was used to calculate the transmittance under the current fogconcentration and judge whether the fog is stable Wait untilthe fog stayed steady and the transmittance reached thedemanded stable value (20 40 60 80 and 100)

In Step 3 when the fog chamber was in a certaindemanded condition (1 of 4 illuminances times 5 transmit-tances) subjects were asked to observe the visual chart andprovide the number of lines of the smallest E they could seeclearly and distinguish the direction To quantify the resultssix lines of E indicate six score levels six points for thesmallest line and one point for the largest line respectively

33 Effects of CCTs Figure 13 shows the experimentalprocedure As the effect of CCTon visual clarity is relativelyinsignificant the CCT that can provide higher perceptionluminance in a certain condition (the same fog concen-tration and the same luminance) was selected by means ofpairwise comparison Seven CCTs were sorted according tothe degree of visual clarity they provided and were scored inorder to make the experimental results more intuitive

In Step 1 LEDs with seven kinds of CCTs were adjusted toa demanded illuminance level under the absence of fog )eposition and angle of LEDs are fixed so that each time twokinds of LEDs which were going to be compared were placedon both sides of the chamber and the illuminance of the twokinds of LEDs remained the same as the value set before

Wood

Fog generator

Organic glass

LED Light source(CRI = x and y)

CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass

Fog generator Illuminometer

CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)

Figure 11 Schematic diagram of experimental setup (a) Overview of experimental facility (b))e section of the front view (c))e sectionof top view

Figure 12 )e experimental situation


In Step 2 the fog generator released fog into thechamber Wait until the fog stayed steady Because the upperpart of the experiment used 6500K as the light source inorder to maintain consistency 6500K was still used in thispart of the experiment as the reference of the fog concen-tration and the calculation of the transmittance

In Step 3 the LEDs were switched from one CCT toanother Subjects were first asked to observe the smallest linewhich could recognize the direction of the E in the visualchart )en they were asked to choose between the LEDsbefore switching and the LEDs after switching which canprovide a clearer vision when observing the visual chart)ere was always only one kind of LED that is bright duringthe experiment

Seven CCTs were sorted by the method of selection sortas shown in Figure 14 A randomized order of seven kinds ofLEDs was prepared in advance to ensure the accuracy ofexperimental data Firstly the first CCTand the second CCTwere selected for comparison as the experimental proceduredescribed above )e CCT that can provide higher visualclarity was selected (no 1 in Figure 14) to be compared withthe third CCT When all seven CCTs were compared theCCT that can provide the highest visual clarity was selected(no 3 in Figure 14))en the above steps were repeated withthe remaining six CCTs to select the CCTwhich can providethe highest visual clarity among the six CCTs In this way theseven CCTs can be arranged according to the magnitude ofthe visual clarity (as shown in the third part of Figure 14) Toquantify the results the seven kinds of LEDs were graded inorder with seven points for the clearest and one point for theleast clear

34 Experimental Results Figure 15 shows the effects ofluminance and fog concentration on human eye per-ception luminance when using 6500K of LED )e the-oretical calculation results in Figure 15(a) are taken fromFigure 10)e smallest E that the subjects could see clearlyand distinguish the direction is indicated by the scores inFigure 15(b) )e higher the scores the better the visualclarity

Figure 16 shows a part of the experimental results andthe values of Lf calculated in Figure 10)e rest of the resultsnot presented in the figure have a similar pattern)e resultsof the experiment were taken as the average of 50 subjects)e dispersion of the data was estimated in terms of standarddeviation In Figure 16 Y-axis on the left shows the levels ofperception luminance under different fog concentrations

and illuminance without fog and the one on the right showsthe results of Lf

4 Discussion

Comparing Figures 15(a) and 15(b) it is concluded that thecurvilinear trends are substantially the same When lumi-nance or transmittance increases the perception luminanceor the score increases )at is to say when the lightingenvironment or visibility is well the human eye can obtainbetter visual clarity

In Figure 15(b) when L 4 cdm2 and T100 and80 the standard deviation is 0 and the scores are 6 )is isbecause when the luminance level is high all the subjects candistinguish the minimum line of the visual chart When theluminance and transmittance are very low (L 1 cdm2T 20) the standard deviation indicates that some subjectscan distinguish the second largest line of visual chart andothers can only distinguish the largest line indicating thatthe subjects have different ability of visual distinction underlow luminance and low fog transmittance In the lower leftcorners of the figure (L 1 cdm2 T 20 40 and 60)the trend of the curve is growing slowly indicating that

A randomized order

Process of comparison

gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7

Figure 14 )e method of selection sort

EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3

Figure 13 )e experimental procedure


under such conditions subjects can only distinguish thelarger lines

Combining these two figures it can be inferred thatluminance and fog transmittance greatly affect the clarity ofthe human eye When the luminance is lowered or the fogconcentration is increased it will cause a decrease in visualclarity When the luminance level is high as the fogtransmittance increases the visual clarity will decrease moreseverely High fog concentration environment seriouslyaffects driverrsquos visual clarity Visual clarity can be improvedto some extent by increasing the luminance but this methodis restricted When the fog concentration is high the degreeof improvement in visual clarity is smaller

In Figure 16(a) for example according to the clarityof visual chart observed by subjects the seven CCTsare ranked from large to small 5700Kgt6500Kgt 4500Kgt 5000Kgt 4000Kgt 3500Kgt 3000K Al-though there are some errors between Lf obtained by the-oretical calculation and the order of CCTs obtained byexperiment it is not difficult to deduce the rule that thevisual clarity increases with the increase of CCT whichverifies the theoretical calculation results )e errors may becaused by the little influence of CCT on perception lumi-nance which cannot be determined by human eyes )edifference in perception luminance between two adjacentCCTs is about 002 cdm2 It seems that CCTs has little effecton visual clarity when compared to luminance and fogconcentration However the subjective luminance percep-tion is a psychological quantity rather than a physicalquantity When the ambient luminance is lower the humaneye can detect more subtle changes in luminance )at iswhy the subjects were able to distinguish between sevendifferent CCTs in the experiment In a real tunnel when the

luminance is fixed and the fog concentration is high theeffect of CCTon the clarity of human eyes can no longer beignored for safe driving

It can be seen from Figure 16 that the mean score ofclarity increases as CCT increases under a certain concen-tration of fog and illuminance As the transmittance or theilluminance decreases the curves become more linear andthe standard deviations decrease which means that under acondition with high concentration of fog (low transmit-tance) or a low luminance (dark environment) the effectthat LEDs with higher CCT can provide higher clarity ismore obvious )e results are consistent with the theoreticalanalysis It can be concluded that LED with higher CCTwillprovide higher visual clarity to human eyes in a certain fogconcentration and luminance environment under mesopicvision As the common range of CCT of LED is 3000K to6500K 6500K is recommended as a more reasonable CCTfor the interior zone of tunnel

In a real tunnel luminance is still the main factor forsafety )e design of luminance requires a trade-off betweenenergy saving and traffic safety Fog concentration can beunderstood as equivalent luminance attenuation and it alsohas an important impact on safety By contrast the CCT haslittle influence on the traffic safety and LED with high CCTcan slightly improve the visual clarity In addition to im-proving the traffic safety in a tunnel from the perspective oflighting it is also possible to improve the safety by limitingthe vehicle speed (reduces visual reaction time) and im-proving the materials of walls and roads of tunnels (increasevisual contrast) Considering that the vehicle speed andlayout of lamps in the tunnel can cause a flickering seizureamongst drivers and passengers by generating cyclicalrepetitions of light flows [27] while ensuring that luminance

Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)

Figure 15 )e impact of the luminance and the concentration of fog on perception luminance (a) )e theoretical calculation results ofperception luminance under different luminance and fog concentration CCT 6500K (b))e experimental results of the average scores of50 subjects on visual perception under different luminance and fog concentration CCT 6500K Error bars indicate standard deviation


and lighting uniformity are in accordance with tunnellighting specifications the placement spacing of lampsshould be considered to prevent the flickering problem intunnels According to the luminance requirements of theinterior zone using low-power LED with dense distributionwill save energy and ensure traffic safety )e effect of CCTon flickering seizure can be further studied

5 Conclusion

In this paper the effects of LEDs with seven CCTs onperception luminance are studied considering fog trans-mittance and mesopic vision in tunnel from the point ofview of energy saving and traffic safety Firstly the formulafor calculating perception luminance was proposed and the

transmittance of nine monochromatic LEDs was obtainedby an experiment And then it was applied to LEDs withseven CCTs composed of multispectrum )e SPDs of theseven CCTs were measured by spectral radiance meter underthe absence of fog Comparing several different mesopicvision models the MES2 model was selected to calculate themesopic spectral luminous efficiency function of human eye

)en the perception luminance was calculated con-sidering different levels of fog and luminance in mesopicrange )e results show that LEDs with higher CCTs (about6500K) can provide higher perception luminance Lumi-nance and fog concentration have more influence on per-ception luminance compared with CCT Higher luminanceor lower fog concentration can obtain higher perceptionluminance

ScorePerception luminance

Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)

Figure 16 )e Y-axis on the left shows the levels of visual clarity using different CCTs under different fog concentrations and illuminancewithout fog)e Y-axis on the right shows the theoretical calculation results of Lf (a) T100 Li 40lx (b) T 60 Li 20lx (c) T100Li 20lx (d) T 40 Li 20lx Error bars indicate standard deviation


Finally an experiment was conducted to measure thevisual clarity of human eyes )e visual clarity is indirectlyrepresented by the effect of LEDs on perception luminanceunder various CCTs and different levels of luminance andfog concentration )e results showed that LED with highCCT (6500K) will always provide higher visual clarity tohuman eyes in a certain fog concentration and luminanceenvironment High luminance and transmittance can pro-vide the subjects with better visual clarity whose effect ismuch greater than CCTs In foggy environments increasingluminance helps subjects improve visual clarity but theimprovement becomes more restricted as transmittancedecreases

)ese results can provide a reference for tunnel lightingconsidering mesopic vision and fog conditions In the in-terior zone of tunnel drivers can obtain higher visual clarityand safety index by increasing luminance (more energyconsumption) or decreasing fog concentration (strength-ening tunnel ventilation or regularly cleaning the dust insidethe tunnel) When the fog concentration is too high theeffect of increasing the luminance to increase the visualclarity will become less obvious If the fog concentration inthe interior zone is too high it is not recommended to openthe tunnel to traffic for safety )e effect of CCT is relativelyinferior to luminance and fog concentration When de-signing a tunnel while putting into consideration the effect ofLEDs on the perception luminance of the human eye orvisual clarity in foggy conditions which kind of CCT isapplied does not make much difference But LED with aCCT of 6500K is recommended as it still provides bettervisual clarity in a way if a comparison is to be made )eabove content provides reference for the guideline of tunnellighting for energy saving traffic safety and the selection ofCCT of current popular lighting luminaire LED

Data Availability

)e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

)e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

)is paper was supported in part by the National NaturalScience Foundation of China under Grant no 61701069 andthe Fundamental Research Funds for the Central Univer-sities of China under Grant nos 3132019340 and3132019200

References

[1] Commission Internationale de lrsquoEclairage CIE Tunnel En-trance Lighting A Survey of Fundamentals for Determining theLuminance in the -reshold Zone p 61 CIE PublicationVienna Austria 1984

[2] European Committee for Standardization Lighting Applica-tions-Tunnel Lighting European Committee for Standardi-zation Brussels Belgium 2003

[3] Commission Internationale de lrsquoEclairage CIE Guide for theLighting of Road Tunnels and Underpasses p 88 CIE Pub-lication Vienna Austria 2004

[4] China Merchants Bureau Chongqing Transportation Researchand Design Institute Co Highway Tunnel Lighting DesignRules JTGT D702-01-2014 Peoplersquos Communications PressCo Chongqing China 2014

[5] L Moretti G Cantisani P Di Mascio and S Caro ldquoTechnicaland economic evaluation of lighting and pavement in Italianroad tunnelsrdquo Tunnelling and Underground Space Technologyvol 65 pp 42ndash52 2017

[6] S He B Liang G Pan F Wang and L Cui ldquoInfluence ofdynamic highway tunnel lighting environment on drivingsafety based on eye movement parameters of the driverrdquoTunnelling and Underground Space Technology vol 67pp 52ndash60 2017

[7] S Schonour B Newell and V Riedinger ldquoEssentials of de-signing with LEDs LED lighting design has many advantagesover previous lighting sources enabling designers to delivermore to their clientsrdquo Consulting-Specifying Engineer vol 55pp 8ndash13 2018

[8] G Lan and L Bo ldquoStudy on lighting control system of thetunnel on expresswayrdquo Microcomputer Information vol 25pp 38-39 2009

[9] L M Gil-Martın A Pentildea-Garcıa E Hernandez-Montes andA Espın-Estrella ldquoTension structures a way towards sus-tainable lighting in road tunnelsrdquo Tunnelling and Under-ground Space Technology vol 26 no 1 pp 223ndash227 2011

[10] F Salata I Golasi S Bovenzi et al ldquoEnergy optimization ofroad tunnel lighting systemsrdquo Sustainability vol 7 no 7pp 9664ndash9680 2015

[11] G Cantisani P Di Mascio and L Moretti ldquoComparative lifecycle assessment of lighting systems and road pavements in anItalian twin-tube road tunnelrdquo Sustainability vol 10 no 11p 4165 2018

[12] L Moretti G Cantisani L Carrarini F Bezzi V Cherubiniand S Nicotra ldquoItalian road tunnels economic and envi-ronmental effects of an on-going project to reduce lightingconsumptionrdquo Sustainability vol 11 no 17 p 4631 2019

[13] Commission Internationale de lrsquoEclairage CIE MesopicPhotometry History Special Problems and Practical Solutionsp 81 CIE Publication Vienna Austria 1989

[14] C S Jae Y Hirohisa and S Satoshi ldquoChange of color ap-pearance in photopic mesopic and scotopic visionrdquo OpticalReview vol 11 pp 265ndash271 2004

[15] M Islam R Dangol M Hyvarinen P Bhusal M Puolakkaand L Halonen ldquoUser acceptance studies for led officelighting lamp spectrum spatial brightness and illuminancerdquoLighting Research amp Technology vol 47 no 1 pp 54ndash79 2013

[16] M Viikari W Chen M Eloholma L Halonen and D ChenldquoComparative study of two visual performance based mesopicmodels based on reaction time and contrast threshold datardquoLight amp Engineering vol 14 pp 21ndash32 2006

[17] X Li Z J Shang Y C Song W Le and Y L Xiao ldquo)emesopic effect of different color temperature LED lightsources on road lightingrdquo in Proceedings of the Communi-cations and Photonics Conference and Exhibition pp 343-344Shanghai China December 2010

[18] Z J Huai Z J Shang C Liang and Y Kun ldquoResearch on thelighting performance of led street lights with different color


temperaturesrdquo IEEE Photonics Journal vol 7 no 6 Article ID1601309 2015

[19] F Du J Weng Y-k Hu and X-y Cai ldquoStudy of road tunnelthreshold zone lighting reduction coefficientrdquo Journal ofCentral South University vol 25 no 9 pp 2040ndash2048 2018

[20] K Otas V J Pakenas and A Vaskys ldquoInvestigation of LEDlight attenuation in fogrdquo Elektronika Ir Elektrotechnika vol 5pp 47ndash52 2012

[21] S S Zeng S Z Jin Y R Wang C S Shi and Y H LuldquoPenetration properties of led light sources in water fog andsea fogrdquo Acta Photonica Sinica vol 42 pp 1140ndash1146 2013

[22] K Brandon A Juan and C Christian ldquoFog attenuationanalysis of visible band for free space optical linkrdquo in Pro-ceedings of the Photonics Society Summer Topical MeetingSeries pp 156-157 Newport Beach USA July 2016

[23] K Liu ldquoStudies of the high-power white LEDs with low Tc andhigh Rardquo Advanced Display vol 21 pp 39ndash43 2010

[24] C T Guo ldquo)e main mechanism of dark adaptation ofhuman eyesrdquo Journal of Sichuan Teachers College vol 2pp 94ndash96 1984

[25] D A Tipton ldquoA review of vision physiologyrdquoAviation Spaceand Environmental Medicine vol 55 no 55 pp 145ndash1491984

[26] Commission Internationale de lrsquoEclairage CIE RecommendedSystem for Mesopic Photometry Based on Visual Performancep 191 CIE Publication Vienna Austria 2010

[27] G Dondi V Vignali C Lantieri and G Manganelli ldquoEffectsof flickering seizures on road drivers and passengersrdquo Pro-cediamdashSocial and Behavioral Sciences vol 53 pp 711ndash7202012


many studies on energy saving of tunnel lighting In 2011Gil-Martın [9] presented tension structures for tunnel tosave energy in the most energy requiring zone (the thresholdzone) and reduce the number of luminaries In 2015 Salata[10] presented that LEDs are suitable for the interior zonedue to their luminous efficiency )anks to their longerservice life they reduce maintenance expenses In 2018Cantisani [11] computed and compared the environmentalimpacts of two lighting systems LED and high-pressuresodium (HPS) in a twin-tube road tunnel He presented thatalthough LEDs cost more in terms of construction andinstallation than HPS they cost less to maintain later In2019 he calculated the energy savings from replacing HPSswith LEDs in Italyrsquos Greenlight project )e results showedthat the new lighting systems will reduce electricity con-sumption by up to 50 of the current values [12] Althoughenergy saving is an essential issue in tunnel lighting designsafety should also be taken into consideration

In the past few years our laboratory has providedlighting design for several tunnels of Heda highway in Jilinprovince of China and accumulated some practical engi-neering experience and problems to be improved )e de-partment of tunnel lighting design and management paysgreat attention to the selection of CCTof LED but there areno official guidelines for reference )erefore it is mean-ingful to explore the effect of CCT on human vision Lu-minance is the main influence factor of safety in tunnellighting Two main factors should be considered for safedriving in the interior zone of a tunnel considering fogcondition human eye perception and transmittance of LEDswith different CCTs in fog condition

)e luminance perceived by human eye is different whenthe ambient luminance and wavelength of light are differentHuman vision is divided into photopic vision scotopicvision and mesopic vision according to the visual phe-nomena caused by light of different wavelengths acting onvisual organs in different luminance ranges [13ndash15] Pho-toreceptor cells in the retina can be divided into two typescones and rods )e luminance range of photopic vision isabout above 3 cdm2 when cones play a major role In thiscase the human eye can distinguish the details and colors ofobjects )e luminance range of scotopic vision is aboutbelow 10minus3 cdm2 when rods play a major role In this casethe human eye can only distinguish light and dark and theability to distinguish details and colors of objects is greatlyreduced Most of the luminance of tunnel lighting belongs tothe range of mesopic vision when both types of cells worksimultaneously in a specific proportion )e mesopicspectral luminous efficiency function varies depending onthe luminance and the interaction between cones and rodsdiffers with luminance levels Several researches concernedwith mesopic vision have been carried out in recent years In2006 Viikari [16] and others measured the reaction time andcontrast threshold to evaluate mesopic visual performance indifferent spectral conditions In 2011 Li [17] and otherspresented that the higher CCT of LEDs have better visualeffects by calculating the mesopic equivalent illumination ofthe different sources In 2016 Huai [18] conducted a test oncolor discrimination and presented that the human eyersquos

ability to distinguish colors improves as CCT increases inmesopic condition In 2018 Du [19] studied the overallluminance performance and indicated that LEDs with highCCT have better luminance performance in lighting re-duction coefficient in threshold zone of tunnel All the abovestudies satisfied the mesopic visual characteristics undergeneral conditions As tunnels are prone to the phenomenonof low visibility it is necessary to consider the effect of fogwhen studying the mesopic vision in tunnel

)e value of CCT is determined by the spectrum of LED)e transmittance of light in fog is affected by the wave-length of light source)erefore it can be inferred that LEDswith different CCTs provide different visual perception infog Some researchers studied the relationship betweenmonochromatic lights and transmittance in fog In 2012Otas [20] and others presented an experimental investiga-tion of the characteristics of the propagation of light emittedby various colors in artificial fog with varying density )eexperiment showed that the light of shorter wavelengths(blue and green) is seen to be less attenuated by scatteringthan that of longer wavelengths In 2013 Zeng [21] andothers researched the penetration properties of LED lightsources in water fog and sea fog showing that the trans-mittance of yellow LEDwas the best followed by blue greenand red In 2016 Brandon [22] and others studied the at-tenuation characteristics of LEDs with six different wave-lengths in a controlled fog chamber )ey got the result thatthe red light has the least attenuation followed by yellow andgreen )e blue light had the worst performance Reaching aunified conclusion about the relationship between wave-length and transmittance from the above researches is hardHuai [18] studied the effect of three CCTs (1870K 2985K and5020K) on penetration properties in fog and presented thatlow-color-temperature (around 3000K) LEDs are moresuitable for street lighting by calculating the transmittanceMost studies of light transmittance are concerned withmonochromatic light not with CCT As a result we shouldconsider the influence of LED with different CCTs on boththe transmission and the mesopic spectral luminous effi-ciency function on tunnel lighting )e most sustainableluminaire in tunnel LED was studied and the impact ofCCT on perception luminance in the interior zone of thetunnel considering different levels of luminance and fogconcentrations was explored for traffic and transport safety)e calculation and experimental results showed that highluminance or low fog concentration could provide highperception luminance High CCTs (about 6500K) couldprovide higher visual clarity But the effect of CCT is rela-tively inferior to luminance and fog concentration )eseconclusions provide reference for tunnel lighting designguidelines for traffic safety energy saving and the selectionof CCTs

2 Theory of Perception Luminance

Considering fog conditions in tunnel the perception lu-minance of human eye is affected by the mesopic spectralluminous efficiency function the spectrum and luminanceof LED and the fog transmittance Human eye perception



Lf 1113946780

380kmVmes(λ)L

lowaste (λ)dλ (1)

Lp 1113946780

380683V(λ)L

lowaste (λ)dλ (2)
















Vmes(λ 555 nm) (4)



(5)




a2 + b2SP

1113968


Vprime λ0( 1113857 1113946 V(λ)Le(λ)dλ (8)

3000K 3500K 4000K 4500K 5000K 5700K 6500K


Abso

lute

spec

tral

pow

er d

istrib

utio

n(W

srlowast

m2 )

400 500 550 600 650 700 750450Wavelength (nm)

00000

00001

00002

00003

00004

00005

00006

00007

00008

00009

3000K3500K4000K4500K

5000K5700K6500K


400 450 500 550 600 650 700 750350Wavelength (nm)

00

02

04

06

08

10

Rela

tive l

umin

ous i

nten

sity




Fog chamber

MonochromaticLED

Illuminometer

Fog generator








3 Experiment


Reference light

450 475 505 520 570 595 640 660 -- --420Wavelength (nm)

00

02

04

06

08

10

Tran

smitt

ance

1008060

4020


L mes

ndashLp (

cdm

2 )


000

005

010

015

020

025

030


SP = 14SP = 20SP = 23



C Lb minus Lt

Lb

(9)







T(λ)

Le(λ)

SP


(7)(6) (5) (4)





CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)


2cdm2

3cdm2

4cdm2

Photopic vision






Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References
































Lf 1113946780

380kmVmes(λ)L

lowaste (λ)dλ (1)

Lp 1113946780

380683V(λ)L

lowaste (λ)dλ (2)
















Vmes(λ 555 nm) (4)



(5)




a2 + b2SP

1113968


Vprime λ0( 1113857 1113946 V(λ)Le(λ)dλ (8)

3000K 3500K 4000K 4500K 5000K 5700K 6500K


Abso

lute

spec

tral

pow

er d

istrib

utio

n(W

srlowast

m2 )

400 500 550 600 650 700 750450Wavelength (nm)

00000

00001

00002

00003

00004

00005

00006

00007

00008

00009

3000K3500K4000K4500K

5000K5700K6500K


400 450 500 550 600 650 700 750350Wavelength (nm)

00

02

04

06

08

10

Rela

tive l

umin

ous i

nten

sity




Fog chamber

MonochromaticLED

Illuminometer

Fog generator








3 Experiment


Reference light

450 475 505 520 570 595 640 660 -- --420Wavelength (nm)

00

02

04

06

08

10

Tran

smitt

ance

1008060

4020


L mes

ndashLp (

cdm

2 )


000

005

010

015

020

025

030


SP = 14SP = 20SP = 23



C Lb minus Lt

Lb

(9)







T(λ)

Le(λ)

SP


(7)(6) (5) (4)





CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)


2cdm2

3cdm2

4cdm2

Photopic vision






Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References


































Vmes(λ 555 nm) (4)



(5)




a2 + b2SP

1113968


Vprime λ0( 1113857 1113946 V(λ)Le(λ)dλ (8)

3000K 3500K 4000K 4500K 5000K 5700K 6500K


Abso

lute

spec

tral

pow

er d

istrib

utio

n(W

srlowast

m2 )

400 500 550 600 650 700 750450Wavelength (nm)

00000

00001

00002

00003

00004

00005

00006

00007

00008

00009

3000K3500K4000K4500K

5000K5700K6500K


400 450 500 550 600 650 700 750350Wavelength (nm)

00

02

04

06

08

10

Rela

tive l

umin

ous i

nten

sity




Fog chamber

MonochromaticLED

Illuminometer

Fog generator








3 Experiment


Reference light

450 475 505 520 570 595 640 660 -- --420Wavelength (nm)

00

02

04

06

08

10

Tran

smitt

ance

1008060

4020


L mes

ndashLp (

cdm

2 )


000

005

010

015

020

025

030


SP = 14SP = 20SP = 23



C Lb minus Lt

Lb

(9)







T(λ)

Le(λ)

SP


(7)(6) (5) (4)





CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)


2cdm2

3cdm2

4cdm2

Photopic vision






Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References




































3 Experiment


Reference light

450 475 505 520 570 595 640 660 -- --420Wavelength (nm)

00

02

04

06

08

10

Tran

smitt

ance

1008060

4020


L mes

ndashLp (

cdm

2 )


000

005

010

015

020

025

030


SP = 14SP = 20SP = 23



C Lb minus Lt

Lb

(9)







T(λ)

Le(λ)

SP


(7)(6) (5) (4)





CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)


2cdm2

3cdm2

4cdm2

Photopic vision






Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References































C Lb minus Lt

Lb

(9)







T(λ)

Le(λ)

SP


(7)(6) (5) (4)





CCT (K) SP ratio3000 121913500 149024000 153904500 178935000 181745700 189776500 20232

530 535 540 545 550 555

680

685

690

695

700

705

710

3000K3500K4000K4500K

5000K5700K6500K

Photopic vision

Scotopic vision

400 450 500 550 600 650 750350Wavelength (nm)

0

200

400

600

800

1000

1200

1400

1600

1800

Spec

tral

lum

inou

s effi

cien

cy (l

mW

)


2cdm2

3cdm2

4cdm2

Photopic vision






Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References


































Equation(2)~(8)

Equation(1) and (3)

400 500 600 7000

200

400

600

800

400 500 600 70000000

00002

00004

00006

00008

400 500 600 700000204060810

T(λ)


Lf


Perc

eptio

n lu

min

ance

(cd

m2 )


3000k3500k4000k4500k5000k5700k

6500k4cdm2

3cdm2

2cdm2

1cdm2

00

05

10

15

20

25

30

35

40












Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References






































Wood

Fog generator

Organic glass


CRI =

x

(a)

E

Wood

Organic glass

LED Light source

Fog

Illuminometer

(b)

Organic glass


CCT

= x

K

CCT

= y

K

CCT

= y

K

CCT

= x

K

E

(c)










4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References





































4 Discussion



A randomized order


gt

gt gt gt gt

Sorted by Lf

lt

gt

gt

lt

1

1 1

1

2

2

22

3

3 3

33

3

4

4

4

4

5

5

6

6

6 6

7

7


EE

3000K~6500K

10203040 lx

6500K

T = τ

E

α (K)

E

β (K)

Comparison1 2 3









Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References





































Perc

eptio

n lu

min

ance

(cd

m2 )


0

1

2

3

4

4cdm2

3cdm2 2cdm2

1cdm2

(a)


4cdm2

3cdm2 2cdm2

1cdm2

1

2

3

4

5

6

Scor

e(b)




5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References
































5 Conclusion





Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

400

401

402

403

404

405

406

(a)


Perc

eptio

n lu

min

ance

(cd

m2 )

3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

128

130

132

134

136

138

(b)Pe

rcep

tion

lum

inan

ce (c

dm

2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8

Scor

e

202

204

206

208

210

212

(c)

Perc

eptio

n lu

min

ance

(cd

m2 )


3500K 4000K 4500K 5000K 5700K 6500K3000KCCT

0

1

2

3

4

5

6

7

8Sc

ore

102

104

106

108

110

112

114

(d)





Data Availability




Acknowledgments


References

































Data Availability




Acknowledgments


References































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