light beam vs heat ray

light beam and heat ray both are nouns.

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

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

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

light beam (noun)	heat ray (noun)
a column of light (as from a beacon)	a ray that produces a thermal effect