You are presented with the quiz "What is used for used for seeing in the dark?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "alight bulb is used for seeing in the dark" and "incandescent lights heat a metal filament that radiates light inside a glass bulb". 

So, what's the best answer to the question?


 

   Heating a metal filament.        