Effects of adapting luminance and CCT on appearance of white and degree of chromatic adaptation, part II: extremely high adapting luminance

Abstract

In part I of this work [Opt. Express, 27 ,9276, (2019) 10.1364/OE.27.009276], we carried out an experiment to investigate the effects of adapting luminance and correlated color temperature (CCT) on degree of chromatic adaptation. Under the highest white luminance Lw of 900 cd/m2, an incomplete chromatic adaptation was still found under the 2700 and 3500 K adapting conditions. This motivated us to further increase the adapting luminance to investigate whether a complete chromatic adaptation cannot happen under a low adapting CCT (e.g., 2700 K). In this experiment, we investigated the degrees of chromatic adaptation under 12 adapting conditions, comprising four CCT (i.e., 2700, 3200, 4000, and 6500 K) and three white luminance levels (i.e., Lw of 1200, 2100, and 3000 cd/m2), by asking human observers to adjust the color appearance of a stimulus to the whitest. Such luminance levels of the adapting conditions were never investigated in the past and are assumed to introduce a complete chromatic adaptation. The results clearly show that an incomplete chromatic adaptation still happened under the adapting condition having a CCT of 2700 or 3200 K, though the luminance was so high. The adapting luminance and CCT were found to jointly affect the degree of chromatic adaptation, with a higher degree of adaptation under a higher adapting CCT or luminance level. When the adapting CCT was low (i.e., 2700 or 3200 K), the increase of adapting luminance was found to be able to increase the degree of adaptation more effectively. These findings suggest the necessity to revise the chromatic adaptation transforms (CAT) and color appearance models (CAM) for better characterizing the color appearance of stimulus under different adapting conditions.