Phew! You've made it through another day at the office. You're just about to don your coat and head out into the evening—but your computer's still on. Should you turn it off, or leave it in "sleep" mode? Some say it's better to shut down, since that way it won't be using any power while you're not around. But others say that the process of shutting down and starting up again uses more power than letting your machine sleep. Who's right?
First things first: Turning your computer off, then on again does not use more power than leaving it on in "sleep" mode. "That's a myth," says Bruce Nordman, an energy efficiency researcher at the Lawrence Berkeley National Laboratory. Another myth: Turning your computer on and off is bad for the machine. "In order to do any real damage, you'd have to turn it on and off far more frequently than anyone would ever want to," says Nordman. That said, trying to remember to shut down your machine every night isn't necessarily the most effective energy-savings strategy. Here's why.
Fifteen years ago, when computer manufacturers first experimented with sleep mode (it used to be called "standby"), the energy savings weren't very dramatic. Today things are different: According to energy efficiency expert Michael Bluejay, while in use, the average laptop requires 15-60 watts, while desktops use 65-250 watts, plus an additional 15-70 for the monitor. In sleep mode, however, most laptops use a measly two watts, and desktops with monitors use 5-10 watts, says Nordman. ("Hibernate" modes on some computers use even less energy—for a good rundown on the difference between various power management modes, check out Michael Bluejay's guide.) Because sleep settings use so little energy, Nordman believes that it isn't really worth making a big production out of remembering to shut down your computer every day: "Much more important to make sure that your computer is set to go into power-saving mode after a certain period of idle time."
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