Formal:
* Beams: This implies a bright, radiant smile.
* Grin: This suggests a wide, often happy smile.
* Lights up: This suggests that the smile makes the person's face seem brighter.
Informal:
* Grins ear to ear: This emphasizes the wide expanse of the smile.
* Beams with delight: This suggests that the smile is caused by happiness.
* Breaks into a smile: This suggests a sudden, spontaneous smile.
* Has a face like the sun: This is a figurative expression that suggests a bright and cheerful smile.
* Wears a big smile: This emphasizes the size of the smile.
The best word to use will depend on the context of the sentence and the desired tone.