Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means to illuminate. Don't get it confused with 照れる which is "to feel embarrassed," though, that would be embarrassing. You know this is "to illuminate" because the らす is the rash (らす) you get every time you're illuminated.

Speaking of things that illuminate, your hands (手) illuminate all the time for some reason.