Post:
You have three switches in one room and a single light bulb in another room. You are allowed to visit the room with the light bulb only once. How do you figure out which switch controls the bulb? Write your answer in the comments before looking at other answers.
Comment:
If this were an interview question, the correct response would be "Do you have any relevant questions for me? Because have a long list of things that more deserving of my precious time than to think about this!
If it’s an LED or flourencent bulb they usually have a small amount of glow after turning them off from the phosphor coating. You might be able to catch that instead of the residual heat, but generally it dissipates pretty quickly, and it might be hard to see with one of the other lights on.
Worse, if the LED is wired to the hot side it will just barely glow at all times.