3 Switches

Another, more elegant solution would be to switch 2 lights on for 5 minutes then switch one light off.

Originally posted by iamatiger
Enter the room, replace the leds with bulbs of 3 known different resistances, noting the positions

Exit the room and take apart the switches, then use a multimeter to determine which switch is connected to which bulb.

Originally posted by sonhouse
That way you don't even waste electricity!