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.