From The Focal Encyclopedia of Photography:
Originally Posted by dancqu
The visual experience that is approximately correlated with the luminance of objects seen as light sources. Since brightness is a psychological concept, there are no units of measurement as there are for luminance, a psychophysical concept.
L. Stroebel and R Zakia
The quotient of luminous intensity of an extended surface in a specified direction by the projected area in that direction (i.e., candelas per square meter). The luminance of an extended source or surface is invariant with viewing distance. Luminance is also invariant within a lossless optical system because changes in image size are balanced by inverse changes in solid angle. The luminance of a Lambertian (ideal) diffuser is invariant with viewing angle because the reduced power reflected off-axis is balanced by a reduction in projected area.
Luminance is the property of a source of surface that most closely correlates with the subjective perception of brightness, which, because of adaptation and contrast effects of the visual system, cannot be used as a reliable measure.
Syn: photometric brightness (obsolete)
Last edited by Stephen Benskin; 04-14-2005 at 08:58 PM. Click to view previous post history.