light up phrasal verb ( see also ↑ light )
1 . light something ↔ up to give light to a place or to shine light on something:
The flames lit up the sky.
The fountain is lit up at night.
2 . to become bright with light or colour:
At night the harbour lights up.
As the screen lit up, he typed in his password.
3 .
a) if someone’s face or eyes light up, they show pleasure, excitement etc
light up with
His eyes lit up with laughter.
Her face lit up with pleasure.
b) light something ↔ up to make someone’s face or eyes show pleasure or excitement:
Suddenly a smile lit up her face.
A mischievous gleam lit up her eyes.
4 . informal to light a cigarette:
I watched Paul light up again.