radiancy vs luster

radiancy and luster both are nouns.

Word	Noun	Adjective	Verb	Adverb
radiancy	Yes	No	No	No
luster	Yes	No	No	No

As nouns, luster is a hyponym of radiancy; that is, luster is a word with a more specific, narrower meaning than radiancy:

Other hyponyms of radiancy include gleam, gleaming, glow, lambency, lustre, sheen, shininess, burnish, gloss, glossiness, polish.

radiancy (noun)	luster (noun)
the quality of being bright and sending out rays of light	a surface coating for ceramics or porcelain
	a quality that outshines the usual
	the visual property of something that shines with reflected light