This is the 7488th most frequent Japanese word.
光らせ
"To make shine" or "to brighten."
Here, "光らせ" is used in its causative form, indicating the action of causing the car's surface to shine.
彼は車の表面を光らせた。
He made the car's surface shine.
In this sentence, "光らせ" metaphorically describes enhancing the attractiveness or brightness of her smile.
彼女は笑顔を光らせながら話しました。
She spoke while making her smile shine.
The word "光らせ" here refers to the action of making jewels shine, often through polishing or other artful techniques.