The current specification of a display's viewing angle as the angle within which the contrast ratio is larger than 10:1 appears not to be predictive for the acceptable viewing-angle range obtained from perception experiments. In our search towards a perceptually relevant specification for the viewing angle, the physical characteristics of the display that are most related to the viewing-angle-dependent image quality were analyzed. This was done for two types of liquid-crystal displays and one plasma TV. The results indicate that a combination of the luminance and chromaticity coordinates of the higher gray levels predicts the degradation in image quality as a function of viewing angle. As a consequence, a new definition of a display's viewing-angle range is proposed based on these characteristics. © Copyright 2008 Society for Information Display.