Jae Chul SHIN, Hirohisa YAGUCHI¹ and Satoshi SHIOIRI¹

Graduate School of Science and Technology, Chiba University, 1-33 Yoyoicho, Inage-ku, Chiba 263-8522, Japan
¹Department of Information and Image Sciences, Chiba University, 1-33 Yoyoicho, Inage-ku, Chiba 263-8522, Japan

(Received October 6, 2003; Accepted February 12, 2004)

Mesopic vision describes a range of light levels where vision is mediated by both cones and rods. The appearance of color in mesopic vision differs drastically from that in photopic vision, where only cones mediate visual information. We used a haploscopic color matching technique to investigate the color appearance under various illuminance levels, ranging from photopic to scotopic via mesopic levels. The observers did color matching between a test color chip under various illuminance levels and a matching color stimulus presented on the Cathode-Ray Tube (CRT) display under the photopic illuminance condition. The results showed that not only chroma and lightness but hue of most color chips changed with illuminance. The manner of the hue changed depended on the color of the test chip, while matching points approached a neutral gray with decrease in illuminance level for all test chips. Chroma reduced continuously with decrease of the illuminance level until 0.1 lx for reddish and yellowish color chips or until 1 lx for greenish and bluish ones. Beyond those illuminance levels, chroma was approximately constant. Lightness decreased with decreasing illuminance level for all test chips except bluish color chips, for which lightness did not decrease much in general and even increased in some cases as predicted by the Purkinje shift. The experimental results obtained in the present study provide critical features that should be considered in predicting the appearance of color at low light levels.

Key words: photopic vision, mesopic vision, scotopic vision, color appearance, color matching experiment