Three Lights Puzzle

An electrician finds 3 switches that control 3 lights in a distant room.

He cannot see the lights from the room with the switches.

He needs to figure out which switch controls which light.

You can assume each switch controls only one light, and that each light/switch pair works correctly. (Light is on/off when switch is on/off.)

How can he find the answer in the fewest trips between the switches and the lights without help? 

Which switch, which light?

Which switch, which light?



Turn switch “1” on and leave it.

Leave switch “3” off.

Turn switch “2” on for a minute, then leave off.

Quickly go to the bulbs.

Label the on bulb “1”.

Label the off bulb that is still warm “2”.

Label the off bulb that is cold “3”.

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