illumination vs luminousness

illumination and luminousness both are nouns.

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

As nouns, luminousness is a hypernym of illumination; that is, luminousness is a word with a broader meaning than illumination:

Other hypernyms of illumination include brightness, brightness level, light, luminance, luminosity.

illumination (noun)	luminousness (noun)
painting or drawing included in a book (especially in illuminated medieval manuscripts)	the quality of being luminous; emitting or reflecting light
the luminous flux incident on a unit area
an interpretation that removes obstacles to understanding
the degree of visibility of your environment
a condition of spiritual awareness; divine illumination