 Luminance

A photometric measure of directional light output weighted by a specified luminous-efficiency function, conventionally measured in candela per square metre. It is distinct from illuminance, which concerns light incident per unit area, and from perceived brightness. Chromatic-discrimination experiments must control luminance cues when those cues could reveal the answer.

Luminance is a measure of the amount of light that is emitted, reflected, or transmitted from a given surface area in a specific direction. It is a key concept in the fields of photography, optics, and display technology, as it relates to how bright an object appears to the human eye.