Judged brightness as a function of dark, intermediate, and light adaptation.

33 subjects were randomly assigned to a dark-, intermediate-, or light-adapted condition. They were then presented with two lighted surfaces of different brightness and asked to adjust the comparison stimulus to apparent equality with that of the standard stimulus. Results showed a significant interaction between adaptation level and stimulus intensity. The dark-adapted group showed greater accuracy at low stimulus intensities than at medium or high, while the intermediate- and light-adapted groups were more accurate in judging brightness at medium and high stimulus intensities. Differences in perceived brightness were cited as contributing to this finding.