Luminance is luminous intensity per unit area or equivalently illuminance per solid angle, and is measured in nits (or, to use standard SI terminology, candelas per square meter - the two terms are equivalent). Luminance is often used to describe the brightness of a particular surface as viewed from a particular direction; for example, a computer monitor might be described as having a brightness of 300 nits (but that would likely only be true when viewing straight on instead of at an angle). See here for some common approximate luminance values.

Conversions