Most of us know, it's a good idea to turn off the lights when we're leaving a room - it's good for your energy bill and also good for the planet.
When using Compact Fluorescent Lights, or CFLs, the U.S. Department of Energy says that if you're going to be away from a room for less than 15 minutes, you should leave the light on, if you're going to be away for 15 minutes or more, then turn them off.
That's because CFLs are affected by how many times they're turned on and off.