How to Save 20 Watts while Running an iMac (or another Mac)

Something you don't think about every day, but something that could save you enough change to get a Big Gulp every now and then: You can take a few simple steps to drastically reduce the amount of power consumed by your computer. Especially when you're doing many things at the same time with multiple hard drives and the screen turned on at full brightness!

This article is written specifically for the 24" iMac (late 2008), but applies to pretty much any Mac that uses electricity (read: ALL of them). By following the steps in this article, you can save a bit of power, which translates into saving a small amount of change each month. And who wouldn't like a few extra nickels in this economy?

The Discovery

I recently purchased the APC Back-UPS NS 1250, and one of the most amazing features of the UPS is the ability to see how many watts are being actively consumed by a device plugged into it.

I found the results of my testing to be quite interesting. When I had the iMac running with the screen at full brightness, the computer was using the energy equivalence of an old 100 Watt tungsten (i.e. 'energy sucker') light bulb! I don't typically run the screen this bright, though, because the lighting in my computer room is typically subdued. So I turned the brightness down all the way (a comfortable level for my vision), and looked again. This time, the computer was using about 75 Watts. NICE!

iMac Power Chart (in Watts)
(Big bright chart for visual learners).

Then, I decided to run a few more tests (a full listing is below): I turned off just the screen (I sometimes leave the computer running for remote SSH access when I'm away from the home), I put the computer to sleep, I shut it down, etc. The biggest energy gains had to do with dimming and/or turning off the screen; it seems that the backlight is a monster power drain!

Detailed stats, for those so inclined:

  • Computer on, running a bunch of processes, full brightness = 125 Watts
  • Computer on, highest brightness = 100 Watts
  • Computer on, lowest brightness = 77 Watts
  • Screen turned off (press Shift + Control + Eject) = 30 Watts
  • Computer sleeping = 4 Watts average
  • Computer off = 0 Watts

You can see that the largest gains come in turning down the screen brightness and turning off the screen altogether (if you're just listening to music, of if you need your computer on, but will be away from it for some time). Almost every time I get up from my desk, I hit Shift + Control + Eject to turn off the screen and save many Watts 

Blackle vs. Google

Another measurement I performed was a test of whether Blackle (a darkly-colored Google replacement page) really saved any electricity, as the site's maintainers claim.

I stared at Google full-screen for ten seconds; the power meter stayed at about 77 Watts the entire time. I then loaded Blackle, waited a few seconds, then observed the power meter for another ten seconds. It stayed at about 75 Watts. So... is three watts worth switching? I say no, because I only use Google every now and then for a search, and am immediately sent over to another page. It's not worth the productivity loss to remember to go to instead of using the built-in Google search in Safari or FireFox.

But, one takeaway for this is that you might save a few pennies a year if you use a darker desktop background as opposed to a bright/white one.

What You Can Do

So, what should you do to save energy, save money, and—ahem—do a tiny bit of work (I'm talking infinitismally small) to save the planet?

  1. Turn off your computer when you're not going to use it for a few hours.
  2. Put your computer to sleep when you're not going to use it for a few minutes to a few hours.
  3. Turn off your screen (on a Mac, press Shift + Control + Eject/F12) when you don't need to look at it, but you need your computer to remain on.
  4. Dim your screen down the the lowest brightness you can before your eyes aren't comfortable anymore. (With most new Macs, the brightest settings are way too bright in all but the most glaring lighting situations anyways!).

What benefits does following this advice give you?

  • Save money on your electric bill.
  • Get longer battery life (if you're using a laptop).
  • Create less heat in the room (a lot of this burned up energy is converted to heat).

Any other good energy-saving tips for computer use?


Wow! Very cool site! I used these (I use PC, but still) and it worked very well. I also say if you are using word processing (apple works, Microsoft work/office), turn off auto save unless you need it. that actually eats up about 1 watt. If you have lighted keys on your keyboard and can adjust it, turn off or down. 1 maybe simple one, TURN OFF THINGS WHEN YOU ARE NOT USING THEM (like internet, apps, etc.). Thats all for now!

I always turn the screen of, but I just drag the mousecursor to the corner of the screen (you can arrange that in the preferences) that is even handier.

I love the fact that my mac produces heat, because my room is icecold *_*

I believe this only applies to CRT monitors. Modern LCD screens are always backlit, aren't they?

This applies to both - LED and LCD backlights use variable power, depending on brightness settings.