They would probably be ok. Like Loner Vamp said, don't use halogen lights. I tried that and they do produce intense heat Then I turned the light off at night, and it made the water temperature drop. That was too much of a temp. fluctuation for the betta. Florescent light is better. Have a silk plant or two in there so he can hide in them and get out of the light if he wants to. My betta is really cute when he gets all cozy in the plant!
Let's see...There are some small lights in my DrsFosterSmith catalog. There is one with a 5 watt halogen; this may be small but I still think it could transfer too much heat, especially to a small bowl. The others are florescent and should be ok. They are sold as "desktop aquarium" lights.