The Windowless Room.

Brainteaser Answer 11:

First and foremost, for your own reference, name the switches “a, b and c.”


Turn on switches a and b.

  • Wait 10 minutes.
  • Turn switch b off.
  • Enter the room.
  • Whichever light bulb is now on, is controlled by switch a (the only one, still on).
  • Feel the other 2 light bulbs (carefully).
  • Whichever light bulb is warm is controlled by switch b.
  • The cold light bulb must be controlled by switch c.

All you have to do is think outside the box!