The Effect of Background Luminance and Ambient Illumination on Color Discrimination in a Crt

A matching task was used to measure the effects of ambient illumination, raster luminance, and target size on color discriminability in a CRT display. A set of ten easily distinguishable colors was presented under two conditions of ambient illumination (dark and bright) and two conditions of raster luminance (low and intermediate). Below this set, a target color was presented as either a circle of 1.4 degrees diameter or a line 1.4 degrees high and 7 minutes wide. Observers were required to match this target with the appropriate color presented in the display above. Under the dark ambient illumination, the intermediate raster yielded faster response times and lower error rates than the low raster. Under the bright ambient, significantly more errors were made with the intermediate than low raster luminance. The target circle yielded faster response times and lower error rates than the target line under all conditions. Color discriminability appears best under conditions where the background luminance is intermediate. Consequently, under dark ambient conditions, raster luminance should be set at an intermediate level but decreased as the ambient illumination increases.