Definition of “light (sth) up” - Learner’s Dictionary

light (sth) up

phrasal verb with light uk us /laɪt/ verb (past tense and past participle lit, lighted)

to make a cigarette, etc start burning:

He made himself a coffee and lit up a cigarette.

(Definition of “light (sth) up” from the Cambridge Learner's Dictionary © Cambridge University Press)