You and I are basically asking the same riddle, Legolas: Your problem is which of 4 switches controls
THE light bulb, and my problem is which of 4 switches controls
WHICH of 4 light bulbs. The two problems are essentially the same (if you know the answer to one, you can figure out the other), with the main difference that looking under the door makes solving the 1-bulb problem a no-brainer, but is no help at all with the 4-bulb problem. So let's assume that you're not allowed to look under the door, at least in the 1-bulb problem.
Any real answers yet? Come on, we're intelligent gamers here.
P.S. Oh, let's also assume that 'down' equals 'off,' for all the switches.