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Fact or fiction: Eight Mac energy-saving techniques tested

James Galbraith | April 23, 2013
What if the daily computing practices you follow to save energy end up wasting it instead?

Takeaway: Turning down the brightness on your laptop's screen is an easy way to extend the length of time your laptop can run between charges.

4. 'You'll save energy if you disconnect all your chargers and peripherals when you're not using them.'

Some of your peripherals may continue to suck power when they are turned off but still plugged in; but the Macs we tested did not. When plugged in--charged and idle--at full screen brightness, the MacBook Pro averaged 13.3W. When turned off but plugged in, it had a draw of 0.0W, according to our meter. Our 2011 21.5-inch iMac averaged 82.7W when on but idle, but that figure dropped to an average of 0.1W when the iMac was turned off but still plugged in.

We attached a 27-inch Apple LED Cinema Display to the iMac, plugged both of them into a power strip, and plugged the power strip into the Watts Up meter. This setup drew an average of 136W when idle but still switched on. The power strip alone drew power at a rate of 0.0W with nothing plugged into it. The display drew 0.2W when plugged directly into the power meter but not connected to the iMac. With both the display and iMac plugged into the power strip, but turned off, the power meter reported a 0.5W power draw. When we turned the surge protector's power switch to off, the draw dropped to zero.

Takeaway: Turning off devices is sufficient. The power draw of our charged MacBook Pro plummeted to zero when we turned it off but left it connected to the power meter. Turning off the power strip also brought the power draw down to a zero reading.

5. 'If you use your Mac's default energy settings, you don't need to turn your computer off at the end of the day.'

We found that both the MacBook Pro and the iMac drew power at a rate of around 1W once they were set to sleep.

Takeaway: Though the wattage level wasn't high, both Macs did continue to draw a small amount of power when asleep.

6. 'Your computer sucks in so much power when it starts up that you'll save energy by simply leaving it on.'

A significant spike in energy draw occurs when you boot your Mac, but it settles down very quickly. Our MacBook Pro gobbled up to 40W during the first minute of bootup, but the system's consumption dropped back to its 12W-to-13W average by the 90-second mark.

Takeaway: The Mac doesn't use much power when sleeping, about 16 watt-hours from 5 p.m. to 9 a.m., but that's more than it uses during the first minute of starting up.


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