Appearance and chromaticity of white as a function of retinal illuminance

Abstract

The color-temperature range perceived as absolute white increases with retinal illuminance.1 This implies that the achromatic response of the visual system grows more rapidly than the chromatic response. We studied how the appearance and chromaticity of white changes with retinal illuminance by scaling the achromatic, yellow, and blue sensation components for test lights between 2985 and 9000 K at 0.33, 2.18, and 4.10 log trolands (log td). The foveal test field was 7° of visual angle and was unlimited in duration. After the sensation stabilized (2–5 s) the subject assigned a percentage value to each of the response categories. The total response always equaled 100%. Whenever 100% was assigned to the white category, the subject was forced to choose either yellow or blue. At 4.10 log td both observers showed similar "best whites" (5310 and 4881 K) and a narrow transition zone (1050 and 1450 K) from one chromatic-response category to the other. The relative amounts of yellow, blue, and white were also similar for the full range of color temperatures. One observer maintained a similar "best white" and transition zone at all retinal illuminances, whereas for the second observer the "best white" fell to lower color temperatures, and the transition zone broadened with decreasing illuminance. At 9000 K the percentage of blue was maximal at the intermediate illuminance level, and a similar response pattern was found at 2985 K for yellow. The loss of saturation from 2.18 log td to 4.10 log td is consistent with the results of Hurvich and Jameson and reinforces the notion that the achromatic response increases more rapidly in this range than the chromatic response. Our data suggest that the opposite is true at lower illuminances.