low beam vs light beam

low beam and light beam both are nouns.

Word	Noun	Adjective	Verb	Adverb
low beam	Yes	No	No	No
light beam	Yes	No	No	No

As nouns, light beam is a hypernym of low beam; that is, light beam is a word with a broader meaning than low beam:

low beam: the beam of a car's headlights that provides illumination for a short distance
light beam: a column of light (as from a beacon)

Other hypernyms of low beam include beam, beam of light, irradiation, ray, ray of light, shaft, shaft of light.

low beam (noun)	light beam (noun)
the beam of a car's headlights that provides illumination for a short distance	a column of light (as from a beacon)