In a room there are 3 light bulbs

Outside the room there are 3 switches, each one turns on one of the light bulbs

the door of the room is closed so you can't see inside

you can open the door but then you can't operate the switches anymore (even if you close it again!)

--

can you find out the switch associated with each light bulb?

solution

Can't you just look through the window? ;p

Uh, yes? Use a switch, open door to see which lightbulb is lit up. Close door, repeat.

??

Yes, assuming incandescent lamps. Won't work with led ones.

after you open the door you can't use the switches anymore! please elaborate

Right, which is why you use the switches before you open the door.

please state exactly your actions

I would turn on two of the switches and wait a couple of minutes. Turn off one of the two switches. open the door, lit bulb is the flipped switch, warm bulb is switch just turned off, and cold bulb is one never touched

I understand your point, but it'd still work with standard LED bulbs used to illuminate your home.

this is the correct answer :)

Ok, I've already heard the solution too XD

I already did... But I'll give you a more elaborate explanation.

The switches do not work as long as the door is open. Therefore, you need to use them before you open the door. In order to figure out which switch controls which bulb, you turn them on and off one by one.

Once you've turned on ONE switch, you open the door to see which bulb is lit. Your riddle states that you cannot operate the switches while the door is open, which means you need to close the door every time you want to operate the switches. What your riddle does not say, and which I must therefore assume is not true,is that the bulbs stop working when you open the door. Therefore, I conclude that if you operate a switch prior to opening the door, you will be able to see which bulb is lit up when you open the door (since the door's status has no effect on the bulbs).

TL;DR:

While the status of the door affects the operability of the switches, it does not affect the operability of the bulbs. Well, that's kind of an imperative bit of information you left out there. :)

cut the ropes exactly in half, after you burn 3 ropes you should be at 45 minutes

Yes. Set both ropes on fire, one on both ends. Once the dual one is burned, light the other end of the other rope.
That's 1:30, not 0:45 Do the LED bulbs emit heat as well? I was under the impression they didn't. Thank you.