light up

to illuminate. 

• The lightning lit up the sky.
• The red lamp lights up in case of danger.
• The whole sky lit up and there was an explosion.
• At sunset, the crickets begin to chirp and the fireflies light up the night.

to light a cigarette.

• She sat and lit a cigarette up.
• You know you have a problem when you light up a cigarette while you already have one lit in the ashtray.
• At one time, people would not have hesitated to light up a cigarette in stations, restaurants, or hospital waiting rooms.
• Does it bother you if I light up a cigarette?

to look happy.

• Her face lit up.
• His face lighted up with joy.
• Tom's face lighted up with joy.
• We all need to lighten up a little.
• Tom face lights up whenever he sees Mary.
• Tom's face lights up whenever he sees Mary.
• Tom's face lit up when Mary entered the room.
• Tom's face lit up when he saw the cake Mary had made for his birthday.
• Tom's eyes lit up when Mary walked into the room.