So all I have is this:

If there were only two bulbs, it'd be easy: turn one on and keep one off, go into room and check.

Problem is when 3, because there are two either dark or shining and we can't figure out which is which ...except if the light bulb can get warm (i.e., we use a third instrument to match the number of variables).

So: turn two on, leave them for a minute. Turn one of them off, then go into the room. There will be one light on, which obvs corresponds to the switch that's on. Now we touch the two dark ones, and whichever is still a little bit hot corresponds to the switch we had on but turned off. (The cold dark one = the switch we never turned on)

Am I getting, um, warm???