Leds experiments in paris 1 colour rendering 2 kruithof s rule
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LEDs experiments in Paris 1. Colour rendering 2. 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. WWARGB. WR. RGBA. RGB. LED clusters

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Leds experiments in paris 1 colour rendering 2 kruithof s rule

LEDs experiments in Paris1. 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
Colour rendering - Illumination





  • LED clusters

    RGB 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


Colour rendering discrimination
Colour rendering - Discrimination

  • Distribution of errors



Colour rendering appearance
Colour rendering - Appearance

Distribution of colourfulness ratings

Distribution of hues


Red ->

<- Red


Yellow ->

<- Yellow

Colourfulness rating

<- Green

Green ->

Blue ->

<- Blue

Red ->

<- Red

Colour rendering conclusion
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 with

    Rea 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’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).

Illuminance (log scale)

Correlated colour temperature

Re examination of kruithof s rule objectives
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
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
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
Re-examination of Kruithof’s rule Performance

  • Example of low-contrast acuity

low-contrast acuity (log)


Y in cd.m-2

Re examination of kruithof s rule colour appearance
Re-examination of Kruithof’s rule Colour appearance

  • Example of location of binary hues

Re examination of kruithof s rule sensation scale
Re-examination of Kruithof’s rule Sensation scale

  • Example of lightness sensation

Perceived lightness scale


Y in cd.m-2