Chromatic discrimination in relation to luminance level

Abstract

We have measured the chromatic-discrimination ellipses with different luminances for 66 stimuli distributed throughout the CIE-1931 chromatic diagram. The distribu- tion of these stimuli enabled us to analyze the influence of luminance on discrimination from clearly photopic levels to levels that could enter the mesopic range. The results show a clear influence of the luminance level on the areas of the chromatic-discrimination ellipses. These areas remain al- most constant when the luminance level is clearly photopic, and clearly increase when the luminance diminishes. How- ever, it is not necessary that the luminance level diminish far below 2-3 cd/m 2 to detect a substantial increase in the area of the ellipses. According to our data, within the photopic range appears a transition interval of luminance above which the most pronounced increase in the area of the ellipse would be appreciable. Other parameters char- acteristic of discrimination ellipses, such as orientation and relation to semi-axes, vary with the luminance level, al- though without clearly following any rule.© 2001 John Wiley