I was told once that leaving a compact fluorescent bulb on when you leave a room for short periods actually used less energy than turning it off and then on again because they use more energy to start up than they do to stay on. The figure I was given was 20 minutes of energy use just starting up.

I've never been able to find any hard info on this question, and it'd be nice to know whether or not to turn the lights off when I'm bouncing back and forth between two rooms doing stuff--say, cooking dinner in one and checking email in the other while things are cooking.

Thanks!