Note: This puzzle isn't mine. It appeared on the internet in 1999.

WARNING: This puzzle contains no ambiguity or hidden meanings. Pedants beware, asking silly questions or making odd comments about the color of the character's trousers and such like will not be ignored, but are futile in the solving of the puzzle.

Bob F has been given the job of identifying which of three switches connects to which of three light bulbs. The switches are located in one room, and down the corridor and around several corners (all walls are concrete, the opaque kind, as are the ceilings and floors) is the room with three bulbs. The switches are identical and unlabeled in any way, with the wiring disappearing straight from the switch into the wall and straight to its respective bulb. In any case (for the pedants) the wiring is all the same color.

Bob F thought this would be an easy job, but now its late and everyone has gone home. Now he realizes that once he leaves the room with the switches he can't get back in (the door is of a self-locking type, for which Bob F doesn't have the key.)

How can Bob F, starting in the room with the switches, determine which switch leads to which bulb?

SUPPLEMENTARY NOTES FOR PEDANTS AND THE SARCASTIC
(please skip these notes if you are happy to take the puzzle at face value)
1. No he doesn't have any tools or other devices available to him. In fact, he's naked.
2. No he can't ask anyone else to help, not even his computer. If he does his boss will fire him.
3. No I don't know why his boss is so mean, he just is.
4. No this isn't the sort of puzzle that requires days or weeks to resolve. Nor can the principles of quantum mechanics be applied to bring about a speedy solution.
5. No there is no audiovisual equipment of any kind in either room. They are in fact bare except for the switches and bulbs.
6. Outside the building is a midget with a ruler, a needle and a ping pong ball. He is irrelevant as per items 1 and 2 above.