light beam vs moon ray

light beam and moon ray both are nouns.

Word	Noun	Adjective	Verb	Adverb
light beam	Yes	No	No	No
moon ray	Yes	No	No	No

As nouns, moon ray is a hyponym of light beam; that is, moon ray is a word with a more specific, narrower meaning than light beam:

Other hyponyms of light beam include heat ray, high beam, moon-ray, moonbeam, sunbeam, sunray, laser beam, low beam.

light beam (noun)	moon ray (noun)
a column of light (as from a beacon)	a ray of moonlight