Light the bulbs outside: An everyday logic puzzle

Gaurav Tiwari
1 min readAug 29, 2022


Image from Pixabay


You are inside a room and there are exactly three electric bulbs outside of the room. The three bulbs have their corresponding switches (exactly three) inside the room. You can turn the switches on and off and leave them in any position. How would you identify which switch corresponds to which electric bulb, if you are allowed to go outside and come inside the room only once?


  1. Keep the first bulb (A, say) switched on for a few minutes. This will warm the bulb.
  2. Switch the first bulb off, switch another one (B, say) on, and go outside to the room where bulbs are placed by keeping this bulb (B) on.
  3. When you reach the bulbs, you’ll find that one bulb is lightened up while two others are switched off. Touch both switched-off bulbs and notice which one of them is warm. Using this method you find, bulb A & bulb B and their corresponding switches.
  4. The remaining one switch must correspond to the third bulb.

This puzzle was originally published on my main blog Gaurav Tiwari and has been moved here due to the on-going cleaning.



Gaurav Tiwari

Hello! I am Gaurav Tiwari. I am an entrepreneur, blogger and WordPress developer with expertise in conversion, performance and growth.