1. 照亮；发亮
If you light something up or if it lights up, it becomes bright, usually when you shine light on it.

2. 现出吃惊的神情；露出喜色
If your face or your eyes light up you suddenly look very surprised or happy.

3. 点烟；开始吸烟
If you light up, you make a cigarette, cigar, or pipe start burning and you start smoking it.

1. make lighter or brighter

e.g. This lamp lightens the room a bit

Synonym: lightillumeillumineilluminate

2. begin to smoke

e.g. After the meal, some of the diners lit up

Synonym: fire uplight

3. start to burn with a bright flame

e.g. The coal in the BBQ grill finally lit up

4. ignite

e.g. The sky lit up quickly above the raging volcano

5. become clear

e.g. The sky cleared after the storm

Synonym: clear upclearbrighten