[geoschmo]

This is an old one, I am sure some of you have heard it...

You are standing in front of a room inside of which stands a lamp with a
lightbulb within it. You can not see when the light is on or off until you
enter the room. Once you enter the room you may not come back out again
until you solve this riddle...

Outside the room there are three switches.

You may turn any of the three swithes anyway you want to (but they only
have two positions: On/Off).

You cannot tell when the light goes on, but one of the switches does indeed
turn the light on and off (the light goes on when that particular switch is
in the on position and not so suprisingly off when it's in the off
position), while the other two switches do nothing.

Once you stop turning the switches on and off you must enter the room and
know exactly which switch turns the light on...

How can you do that?

Note: Here are a few answers to possible lines of thought and consequently
questions that people may have...

You have no tools with which to remove the panel nor to examine the wires
within the panel.

You are by yourself.

You cannot use mirrors.

There is no window within the room.

There are no switches or wires that are accesible from within the room.