- Keep the first bulb (A, say) switched on for a few minutes. This will warm the bulb.
- Switch the first bulb off, switch another one (B, say) on, go outside to the room where bulbs are place by keeping this bulb (B) on.
- Where you reach to 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.
- Remaining one-switch must correspond to third bulb.