lighten vs light up

lighten and light up both are verbs.

Word	Noun	Adjective	Verb	Adverb
lighten	No	No	Yes	No
light up	No	No	Yes	No

As verbs, light up is a hyponym of lighten; that is, light up is a word with a more specific, narrower meaning than lighten:

Other hyponyms of lighten include irradiate, illume, illuminate, illumine, light.

lighten (verb)	light up (verb)
make more cheerful through the use of color	introduce light into
become lighter	begin to smoke
alleviate or remove (pressure or stress) or make less oppressive	become clear
become more cheerful	start to burn with a bright flame
reduce the weight on; make lighter	ignite
make more cheerful