Q. My mom used to say that if I’m going to leave a room for just a few minutes, I should leave the lights on because it takes more energy to turn lights off and on in a short period of time than it does to just leave them on. Is that true?

A. Though there is a surge of energy for a fraction of a second when you turn on a light, it is such an insignificant amount that it is not even measurable on a normal meter, says Steve Selkowitz, a lighting expert at the Lawrence Berkeley National Laboratory. So whether you’re leaving for a few hours or just stepping out for a few minutes to grab the mail, Selkowitz says the most energy-efficient strategy is to always shut the lights off.

This article originally appeared in Plenty in April 2007. The story was added to MNN.com in June 2009.

Copyright Environ Press 2007.