LEDs experiments in Paris 1. Colour rendering 2. Kruithof

1
LEDs experiments in Paris1. Colour rendering2.
Kruithofs rule

• F. Viénot, E. Mahler, A. Rambaud, M.-L. Durand,
  C. Boust, J.-J. Ezrati,
• CRCC, Muséum national dhistoire naturelle
• CIE, TC1-69, Stockholm, June 2008

2
Colour rendering - Illumination

• LED clusters
• RGB LEDs RGB
• RGBAmber 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

Solux
3
Colour rendering - Discrimination

• Distribution of errors

RGB
Solux
4
Colour rendering - Appearance

• Distribution of colourfulness ratings

• Distribution of hues

Solux WWRGBA RGB
lt- Red
Red -gt
RGB
lt- Yellow
Yellow -gt
Colourfulness rating
lt- Green
Green -gt
Blue -gt
lt- Blue
lt- Red
Red -gt
5
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.

6
Kruithofs 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.
• Kruithofs 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
7
Re-examination of Kruithofs 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

8
Re-examination of Kruithofs 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 gt 86

9
Re-examination of Kruithofs 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

10
Re-examination of Kruithofs rule Performance

• Example of low-contrast acuity

low-contrast acuity (log)
Illuminations Y in cd.m-2
11
Re-examination of Kruithofs rule Colour
appearance

• Example of location of binary hues

12
Re-examination of Kruithofs rule Sensation scale

• Example of lightness sensation

Perceived lightness scale
Illuminations Y in cd.m-2