I stumbled across something like this on the internet.* No doubt you could find the answer that way, but that’s no fun.
You are in a room with three switches that each control a different [incandescent] light fixture in another room. You cannot see from the switch room into the lamp room. Your task is to determine which switches control which light fixtures, but you may only go into the room with the lights once. How do you determine which switch controls which light?
You do not need any equipment or magic to do this. Yes, you can reach the light bulbs when you enter the lamp room. No doubt someone will answer this in the comments. If not, I’ll post the answer on Monday.