illuminance vs brightness

illuminance and brightness both are nouns.

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

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

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

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