Abstract
An intensity modulated cathode-ray screen of the PPI type used in radar depends on differential brightness discrimination for detection of weak signals. The brightness quantities have been largely unknown, because of photometric difficulties, but it has commonly been assumed that dark adaptation is required to efficient visual detection. Therefore, an experimental test was undertaken of the effects of light-an dark-adaptation on the contrast threshold and on time required for detection of supra-threshold signals appearing on a typical screen (P7 phosphor).