Three Switches Puzzle

Puzzle of the Day 2059 : Three Switches Puzzle

Puzzle 2059 - Three switches Puzzle

You are in the basement of a house where there are are three identical on-off switches.  One of them controls a lamp in the attic, and two of them do nothing.

You have no way to see into the attic or to see reflected light from the attic.  If you go upstairs to the attic, you are not allowed to return to basement.
You are permitted to manipulate the switches all you like, but you are only allowed one single trip to the attic.

How would you tell which switch lights the bulb?