Millions of us who use computers every day have assumed (yes, even those of us who write about energy for a living) that by diligently activating our screensavers not only were we preventing a ghost image from being permanently burned onto our screens, thus extending the life of the monitor, we were also saving energy. Well, we were wrong.

Alan Meier, a researcher at Lawrence Berkeley National Laboratory (LBNL), says it’s past time to disable our screensavers. In fact, the very label “screensaver” is a misnomer. There was a time when cathode ray tube (CRT) monitors were susceptible to burn-through, says Meier, but no longer; and liquid crystal displays (LCDs) never had the problem.

But, even with screensavers’ monitor-saving duty made obsolete, they still save energy, right? No, Meier says. Depending on the display (CRT or LCD), your screensaver consumes 40-100 watts. Worse, the active screensaver may prevent your CPU from going to “sleep” — fleecing you for another 100 watts.

And because so many office workers neglect to turn off their computers and monitors when they leave for the day, screensavers display overnight in idle offices everywhere. Meier cites a 2004 LBNL study that found that in the various buildings surveyed about 20% of the monitors and 60% of the CPUs were left on all night.

To take full advantage of the energy-saving settings available on your computer, Meier recommends ENERGY STAR’s power management primer. The site also includes a power management calculator that displays the reward for activating those power-saving settings in dollars saved and pounds of greenhouse gas emissions prevented.

Now I just need to explain to my wife that my screensaver — a picture of us holding each other on the morning of a hike — needs to be sacrificed in the name of efficiency.