The Classic 3 Lights and 3 Switches Puzzle
- You are standing outside a windowless room containing three identical light bulbs. Outside the room, there are three switches, each controlling exactly one bulb inside.You may flip the switches as many times as you like, but you may only enter the room once. Once inside, you can’t manipulate the switches anymore.
How can you determine exactly which switch controls each bulb?
Show Answer
Answer:
Turn on Switch 1 and leave it on for a few minutes.
This will heat up the bulb it controls.
After a few minutes, turn off Switch 1 and turn on Switch 2.
Now Switch 2 is on, Switch 1 is off, and Switch 3 remains untouched.
Immediately enter the room.
Here’s how to identify the mapping:
The bulb that is ON is controlled by Switch 2 (since only it’s on).
Among the two OFF bulbs, feel each bulb:
The warm (but OFF) bulb is controlled by Switch 1 (it was recently on, so it’s warm).
The cold and OFF bulb is controlled by Switch 3 (it was never touched)
