Magnitude estimation of the brightness of brief foveal stimuli.

Eighteen observers judged the apparent brightness of light flashes that varied in both duration and luminance. The median numerical estimations (made relative to a standard flash) confirmed three principles: the reciprocity between luminance and duration (Bloch's law), the enhancement of brightness at about 50 milliseconds (Broca-Sulzer effect), and the power-law relation between brightness and energy (Stevens's law).