You are in a room with 3 switches.
In the adjacent room there are 3 lamps with light bulbs.
All of the lights are off at the moment.
Each switch belongs to one lamp in the other room.
It is impossible to see from one room to another.
How can you figure out which switch belongs to which lightbulb, if you may enter the room with the bulbs only ONCE?
No help from anybody else is allowed.