radiance vs radiancy

radiance and radiancy both are nouns.

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

As nouns, radiance and radiancy are synonyms defined as:

radiance and radiancy: the quality of being bright and sending out rays of light

Other synonyms of radiance include effulgence, refulgence, refulgency, shine.

radiance (noun)	radiancy (noun)
the quality of being bright and sending out rays of light	the quality of being bright and sending out rays of light
the amount of electromagnetic radiation leaving or arriving at a point on a surface
an attractive combination of good health and happiness