LEDs experiments in Paris 1. Colour rendering 2. Kruithof’s rule

LEDs experiments in Paris

1. Colour rendering2. Kruithof’s rule

F. Viénot, E. Mahler, A. Rambaud, M.-L. Durand, C. Boust, J.-J. Ezrati,CRCC, Muséum national d’histoire naturelle

CIE, TC1-69, Stockholm, June 2008

Colour rendering - Illumination

• LED clustersRGB LEDs “RGB”

RGB+Amber LEDs “RGBA”

two-phosphor cold white LED + Red LED “WR”

two-phosphor cold white LED + two-phosphor warm

white LED + Amber + RGB LEDs “WWARGB”

• Control light : Solux filtered tungsten-halogen lamp

WWARGB

0

0.01

0.02

380 480 580 680 780

Wavelength [nm]

Spe

ctra

l irra

dian

ce (W

/m2)

WWARGBWR

0

0.01

0.02

380 480 580 680 780

Wavelength [nm]

Spe

ctra

l irr

adia

nce

(W/m

2)

WRRGBA

0

0.01

0.02

0.03

380 480 580 680 780

Wavelength [nm]

Spe

ctra

l irra

dian

ce (W

/m2)

RGBARGB

0

0.01

0.02

0.03

0.04

0.05

0.06

380 480 580 680 780

Wavelength [nm]

Spe

ctra

l irr

adia

nce

(W/m

2)

RGB Solux

0

0.01

0.02

380 480 580 680 780

Wavelength [nm]

Spe

ctra

l irr

adia

nce

(W/m

2)

Solux

Colour rendering - Discrimination

• Distribution of errors

Errors of neighbourhood of each cap

0

1

2

3

4

5

6

7

8

9

10

1 4 7 10 13 16 19 22 25 28 31

32 caps

Nu

mb

er

of

err

ors

of

ne

igh

bo

urh

oo

d

Solux WWARGB WR RGBA RGB

RGB

Solux

Colour rendering - Appearance

• Distribution of colourfulness ratings • Distribution of hues

Col

ourf

ulne

ss r

atin

g

Visual appearance experiment

0

1

2

3

4

5

6

7

8

9

10

R Y50R Y G50Y G B50G B R50B R

NCS sample code

Obs

erv

ers

ratin

g

Solux

RGB

RGBA

WR

WWARGB

RGB

Red-BlueRed-BlueRed-BlueR10B




Blue-RedRed-BlueBlue-RedR50B

Blue-RedBlue-RedBlue-RedR60B


Blue-GreenBlue-RedBlue-RedR80B


Blue-GreenBlue-GreenBlue-GreenB

Blue-GreenBlue-GreenBlue-GreenB10G

manquantmanquantmanquantB20G


Green-BlueBlue-GreenBlue-GreenB40G



Green-BlueGreen-BlueBlue-GreenB70G


Green-BlueGreen-BlueGreen-BlueB90G

Green-BlueGreen-YellowGreen-BlueG

Green-BlueGreen-BlueGreen-YellowG10Y

Green-YellowGreen-YellowGreen-YellowG20Y



Green-YellowYellow-GreenYellow-GreenG50Y

Green-YellowYellow-GreenGreen-YellowG60Y

Yellow-GreenYellow-GreenYellow-GreenG70Y



Yellow-RedYellow-RedYellow-RedY

Yellow-RedYellow-RedYellow-RedY10R


Red-YellowYellow-RedRed-YellowY30R


Red-YellowRed-YellowRed-YellowY50R





Red-YellowRed-YellowRed-YellowR

RGBWWARGBSoluxNCS





Blue-RedRed-BlueBlue-RedR50B





Blue-GreenBlue-GreenBlue-GreenB







Green-BlueGreen-BlueBlue-GreenB70G


Green-BlueGreen-BlueGreen-BlueB90G

Green-BlueGreen-YellowGreen-BlueG

Green-BlueGreen-BlueGreen-YellowG10Y




Green-YellowYellow-GreenYellow-GreenG50Y

Green-YellowYellow-GreenGreen-YellowG60Y




Yellow-RedYellow-RedYellow-RedY










Red-YellowRed-YellowRed-YellowR

RGBWWARGBSoluxNCS

Solux WWRGBA RGB

<- Red

<- Yellow

<- Green

<- Blue

<- Red

Red ->

Yellow ->

Green ->

Blue ->

Red ->

Colour rendering - Conclusion

• Colour rendering– either Colour fidelity, colour discrimination– or Colourfulness enhancement

• Different tasks and different visual coding• Results of thiese experiments can be

predicted from CIELAB or CIECAM02

• Agreement withRea Mark S., Freyssinier-Nova Jean P., 2008, Color Rendering: A Tale

of Two Metrics, COLOR research and application, 33: 192-202.

Kruithof’s rule - Background

Kruithof, A. A.: Tubular Luminescence Lamps for General Illumination, Philips Technical Review 6, pp. 65-96 (1941).

Kruithof has examined the illuminance limits between which users find the illumination “pleasant”.

Kruithof’s diagram (Fig. 10) shows the accepted combination of illuminance and colour temperature.

The author states that, globally, a low and high illumination should correspond to a low and high colour temperature, respectively (my translation).Ill

umin

ance

(lo

g sc

ale)

Correlated colour temperature

Re-examination of Kruithof’s ruleObjectives

• Since LED illumination is very flexible in terms of luminous intensity and colour temperature, we have planned an experiment to re-examine this rule, questioning the interpretation and the physiological basis of the “pleasantness” sensation.

• Collaborators– Marie-Lucie Durand, Paris-Orsay University– Elodie Mahler, SNCF, France

Re-examination of Kruithof’s rule Methods

• Light booth equipped with LEDs (cool white, warm white, orange, amber, green, cyan, blue)

• Illuminance : 150, 300 and 600 lx• Correlated colour temperature : 2700, 4000,

6500 K• Optimised CRI > 86

Re-examination of Kruithof’s rule Tasks

• Three type of tasks– Performance (acuity, contrast threshold, reading)– Color perception (hue appearance, colour preference,

cognitive colours)– Subjective feeling (pleasantness, mood, …)

• Methods (depending upon the task)– Scaling, ranking, thresholds, category scaling,

semantic analysis, ANOVA

• 30 young observers

Re-examination of Kruithof’s rule Performance

• Example of low-contrast acuity

IlluminationsY in cd.m-2lo

w-c

ontr

ast

acui

ty (

log)

Re-examination of Kruithof’s rule Colour appearance

• Example of location of binary hues

Re-examination of Kruithof’s rule Sensation scale

• Example of lightness sensation

IlluminationsY in cd.m-2

Pe

rce

ive

d li

ghtn

ess

sca

le

LEDs experiments in Paris 1. Colour rendering 2. Kruithof’s rule

Documents

Transcript of LEDs experiments in Paris 1. Colour rendering 2. Kruithof’s rule