Your question is Light Switches and Bulbs. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
A windowless room contains three identical light fixtures, each containing an identical light bulb. Each light is connected to one of three switches outside the room. Before opening the door you may play with the light switches as many times as you like. After opening the door you may no longer touch a switch. How can you tell which switch goes to which light?