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

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

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  1. 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

  2. Colour rendering - Illumination WWARGB WR RGBA RGB • 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 Solux

  3. Colour rendering - Discrimination • Distribution of errors RGB Solux

  4. Colour rendering - Appearance Distribution of colourfulness ratings Distribution of hues Solux WWRGBA RGB Red -> <- Red RGB Yellow -> <- Yellow Colourfulness rating <- Green Green -> Blue -> <- Blue Red -> <- Red

  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. 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

  7. 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

  8. 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

  9. 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

  10. Re-examination of Kruithof’s rule Performance • Example of low-contrast acuity low-contrast acuity (log) Illuminations Y in cd.m-2

  11. Re-examination of Kruithof’s rule Colour appearance • Example of location of binary hues

  12. Re-examination of Kruithof’s rule Sensation scale • Example of lightness sensation Perceived lightness scale Illuminations Y in cd.m-2

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