To illuminate, to make someone's face show happiness, or to begin smoking a cigarette.
To turn on lights, to make someone's face look very happy, or to start smoking.
4 meanings, ordered from most common to least. Color-coded by CEFR level.
To illuminate or cause something to shine with light.
"Thousands of lanterns lit up the river during the festival."
This little light of mine, I'm gonna let it shine.
— Traditional Gospel song, popularised during the American Civil Rights Movement
For someone's face or eyes to suddenly show joy, excitement, or enthusiasm.
"Her face lit up the moment she saw her grandmother walk through the door."
Her whole face lights up when she talks about her children.
— Common journalistic usage; e.g., The Guardian, various profiles
To light a cigarette, cigar, or pipe and begin smoking.
"He stepped outside and lit up, staring at the city lights below."
To make a place, screen, or system active and bright with display or activity.
"Notifications lit up his phone screen one after another."
To apply a flame or switch on electricity so something produces light — the idiomatic senses extend this to faces and moods.
To turn on lights, to make someone's face look very happy, or to start smoking.
Very versatile phrasal verb with literal and idiomatic senses. The 'face lights up' construction is extremely common and emotionally expressive. The smoking sense is informal but widely understood. Used across all varieties of English.
Natural word combinations native speakers use most often.
The five tense forms you'll use most often.
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