nighttime vs lights-out

nighttime and lights-out both are nouns.

Word	Noun	Adjective	Verb	Adverb
nighttime	Yes	No	No	No
lights-out	Yes	No	No	No

nighttime (noun)	lights-out (noun)
the time after sunset and before sunrise while it is dark outside	(military) signal to turn the lights out
	a prescribed bedtime