Turning lights on and off uses energy, but how long should they be off in order to save energy?

The Mythbusters actually covered this myth! Turning on a light does indeed use more energy than a light bulb that is continually burning, but only for a fraction of a second, and it is minimal. Even if you are going to leave the room for a minute, if you turn off the light you will save energy. If you do that every day for a year, you would save enough energy as a light bulb that has been on needlessly for over five hours!