Perceived brightness as a function of duration of dark-adaptation.

The increasing brightness of white light perceived at constant luminance in the course of dark-adaptation was measured by mean of a direct psychophysical scaling method. The same trend was for all 6 luminances levelled of the experiment. It could be characterized as composed of 2 functions, both growing at a decelerate rate and intersection at about 8 min. A further analysis revealed that the empirical trend could be represented by the sum of 2 logarithmic functions of time.