When the DJ announced a contest, the phones 'lit up'. [=the lights on the phones lit up because many people were calling]
His eyes/face 'lit up' [=he looked very happy and pleased] when she walked in the room.
He 'lit into' his employees for their sloppy work. [=he criticized them very harshly]
(..) you never met? Yeah, but you should've seen her. She was a stunner. - I don't care if fuckin'... - Oh, no, no, she lit up the room. - I don't care if Helen of Troy walks into the room! That's game six! - Oh, Helen of Troy. Oh, my God. And who are these fuckin' friends (..)1997 Good Will Hunting