Outside the room are three switches that are all in the off position.
You cannot see the lightbulbs from the witches.
The lightbulbs are in a room with no windows behind a solid door that leaks no light around it.
How can you determine which switch turns on which lightbulb?
You can only open the door once, and once you open the door, you cannot change the position of any of the switches.
They are ordinary lightbulbs and you are completely by yourself.
How can you do it?