Incandescent bulbs are now obsolete. We are now suppose to use florescent bulbs. They are curly looking things. For less wattage they give more light. Save the environment crap. Your problem is, your not using them for light but for heat. The florescent bulbs give off less heat.

Solution 1, search the internet for incandescent bulbs. Someone must still sell them.
Solution 2, find a new heat source. Bulbs seem like a poor heat source, I think you can do better.