luminance vs luminousness

luminance and luminousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
luminance	Yes	No	No	No
luminousness	Yes	No	No	No

As nouns, luminance and luminousness are synonyms defined as:

luminance and luminousness: the quality of being luminous; emitting or reflecting light

Other synonyms of luminance include brightness, brightness level, light, luminosity.

luminance (noun)	luminousness (noun)
the quality of being luminous; emitting or reflecting light	the quality of being luminous; emitting or reflecting light