Photopic, Mesopic and Scotopic Vision and Changes in Visual Performance

Abstract

Effective vision extends over almost 1000-million-fold range of light levels, but this extraordinary achievement does not come without compromise. First, the range is shared between two different subsystems: the sensitive rod system and the less-sensitive cone system. Second, processes of adaptation regulate sensitivity by trading between improvements in sensitivity at lower light levels, and improvements in spatial and temporal acuity and chromatic sensitivity at higher light levels. Consequently, the processing of spatial, temporal, and chromatic aspects of visual stimuli varies greatly with light level and this variation becomes greater with increasing age. These changes cannot be captured by spectral luminous efficiency functions alone.