Brightness Perception of Surface Colors at Various Illuminance Levels

Abstract

The brightness for 12 test color chips was investigated under various illuminance levels covering 0.01 to 3000 lx. The experimental method was to match the brightness of test stimuli of color chips with a gray scale and to express the brightness by the equivalent lightness of the gray scale. The test stimuli were presented in a foveal 10° and 2° fields. Gray background of value N6 was used. The experimental results showed that the equivalent lightness for the red test col or chip decreased with the decreasing of illuminance. The equivalent lightness for the blue test color chip decreased with the decreasing of illuminance in the photopic range, but it increased with the decreasing of illuminance in the mesopic range. The equivalent lightness for the yellow test color chip did not change in the photopic range, but it decreased with the decreasing of illuminance in the mesopic range. The green test color chip did not show any change in its equivalent lightness. To explain this phenomenon, a formula was proposed by three functions, the rod achromatic channels, the cone achromatic channels and the cone chromatic channels for the equivalent lightness under various illuminance levels.