Fact 1: An incandescent light bulb converts electricity into light by sending electricity through a filament.

Fact 2: Incandescence is light from heat energy.

Given the two facts above, answer the question "what are light bulbs powered by?" with the following options: 
- heat
 - metal
 - wind
 - sun
 - energy
 - magnetism
 - gas
 - cold


 

 heat        