I know, so if you turn one on, let the bulb heat up, turn it off, turn another on, go in to see if the bulb is warm from switch #1 or is still on from switch #2, the question and instructions state that once you are in the room you cannot leave, therefore if the bulb is neither warm or on, you could deduce that it's switch #3. However, if you open the door and look in without actually entering the room you can try all 3 to verify like FiLtH said.