There are three switches in front of you, one of which controls a lightbulb in an isolated room. You can turn any of the switches on or off, but you can't tamper with them. You can only enter the isolated room once, but that's it, and you can't see what's happening in the isolated room without entering.
So in other words, you do what you can turn the switches on and off, and then you view the results. That's it.
How can you tell which switch controls the bulb?
Not only is there a possible answer, but this can also be solved with up to six switches and up to six bulbs, where you figure out which bulb is hooked up to which switch.