illumination vs brightness

illumination and brightness both are nouns.

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

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

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

illumination (noun)	brightness (noun)
painting or drawing included in a book (especially in illuminated medieval manuscripts)	the location of a visual perception along a continuum from black to white
the luminous flux incident on a unit area	the quality of being luminous; emitting or reflecting light
an interpretation that removes obstacles to understanding	intelligence as manifested in being quick and witty
the degree of visibility of your environment
a condition of spiritual awareness; divine illumination