Lights teaser

[kendor]

ok doing the rounds again:

3 pendant lights are inside a room with only one door for entry/escape, there is a 3 gang switch outside the room, one switch controls the red light ,one controls the blue light and one controls the white light.

The problem is you can't see the lights until you have fully entered the room and closed the door, the door has a combination lock on the inside which activates once you enter and close the door and which will only allow the door to open if you enter which switch controls which lamp correctly. how do you work out the combination in order to escape the room? You are not allowed to keep the door ajar it must be closed behind you once you have entered the room.

 

[ninebob]

Switch two of the switches on for a period of time, them switch one of them back off. Then enter the room.

The bulb that is on is obviously controlled by the switch you left on.
Of the other two bulbs, both will be off but one will be warm. This is controlled by the switch you had on for a while. The other bulb will be cold, this is the switch you didn't touch at all.

 

[bethrob99]

Turn on switch 1. wait a couple of minutes and turn on switch two. Enter room immediately and identify which of the two on lights is hottest - switch one, just warming through - switch two, and the other is obviously switch three