brightness vs luminousness

brightness and luminousness both are nouns.

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

As nouns, brightness and luminousness are synonyms defined as:

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

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

brightness (noun)	luminousness (noun)
the location of a visual perception along a continuum from black to white	the quality of being luminous; emitting or reflecting light
the quality of being luminous; emitting or reflecting light
intelligence as manifested in being quick and witty