- In photometry, a measure of the
amount of radiant energy received per unit solid angle per unit time
per unit area of a surface element perpendicular to the direction of
propagation of the radiation. Also known as specific intensity.
- In visual perception, one of the three basic parameters (along with
hue and saturation) that may be used
to describe the physical perception of color.
Intensity is a measure of the energy of the spectral distribution, at
a given point in an image or scene, weighted by the spectral response
of the visual system. Luminance is the energy of the
physical spectrum, but not weighted by the visual response. Brightness
sometimes is used synonymously with either term.
- In radio astronomy, a term
often used much more loosely to mean either the flux
density of an unresolved radio source or the surface
brightness of an extended source.