light up | ˌlight sth ↔ ˈup
1.
( informal ) to begin to smoke a cigarette :
They all lit up as soon as he left the room.
He sat back and lit up a cigarette.
2.
to become or to make sth become bright with light or colour :
There was an explosion and the whole sky lit up.
3.
if sb's eyes or face light up , or sth lights them up , they show happiness or excitement :
His eyes lit up when she walked into the room.
A smile lit up her face.