The quality of being luminous; emitting or reflecting light WordNet 3.0 & Open English WordNet

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. Wikipedia

Photometric measure of the density of luminous intensity in a given direction, measured in candela per square metre. Wikipedia Disambiguation

Photometric measure of the luminous intensity per area of light travelling in a given direction Wikidata

The ability of emitting or reflecting light. OmegaWiki

The amount of light coming from an object. OmegaWiki

The quality of being bright. Wiktionary

The luminous flux emitted in a given direction divided by the product of the projected area of the source element perpendicular to the direction and the solid angle containing that direction (i.e. luminous intensity divided by unit area), measured in stilbs or apostilbs. Wiktionary

Luminous intensity. Wiktionary (translation)

The quality of being luminous. Wiktionary