Abstract

Luminance is defined as the radiance of a source weighted by the spectral luminosity of the CIE standard observer. The definition requires the concept of linearity, formalized in psychophysics as Abney's law. Many psychophysical methods of assessing luminance obey Abney's law; the most famous are heterochromatic flicker photometry and minimally distinct border. These psychophysical functions are interpreted as summed cone activity. Implicit in this interpretation is the concept of a luminance channel, i.e., a specific neural channel, accessible by specific psychophysical techniques, encoding a sensory quality. The concept of a luminance channel has seen many uses in the visual literature. Four distinct interpretations can been differentiated: (1) A theoretical construct: a channel encoding the sensation of luminance, accessed by certain psychophysical techniques and obeying Abney's law. (2) A physiological construct: a neural channel in which specific cells encode luminance at successive levels in the nervous system. (3) An operational construct for stimulus specification: a visual stimulus that may be partitioned into separable luminous and chromatic components. (4) A psychophysical construct: a channel encoding a sensory quality, such as brightness or blackness/whiteness.

© 1990 Optical Society of America