Brightness

(Term of photometry)

The subjective description of luminance.
A perceived characteristics of objects which does not vary directly in a simple mathematical relationship with their physical or measured brightness, which is corretly termed their luminance.

The term brightness is often misused to mean luminance. If so, it should be qualified as "measured" brightness, to distinguish between the absolute attributes ("measured" brightness) and the perceived attributes ("apparent" of "subjective" brightness) of the object in question.