Thursday, June 3, 2010

Display power consumption

I picked up a Kill-a-Watt a while back in hopes of learning more about energy consumption - how much does a second hard drive, increased RAM, or adding a USB 2.0 card increase the current draw on my G4 Power Macs. I'll get to that eventually, but I have done some testing of computer displays - and made some interesting discoveries.

The first one I tested was a 17" Gateway 2000 Vivitron 1770 that I picked up at a moving sale for $3. Who can resist that kind of price? I wondered if it might draw less power than my current monitor, and the Energy Star sticker was encouraging.

My Blue & White Power Mac G3 booted to 800 x 600 resolution at 60.3 Hz, and the Kill-a-Watt reported the display was drawing 90W. Bumping resolution to 1024 x 768 @ 60 Hz, that dropped a bit to 88W. Changing the refresh rate to 70 Hz increased that to 92W. This display has an 1152 x 870 setting - at 75 Hz, it draws 97W. Finally, at 1280 x 1024 and 60 Hz, that drops a bit to 95W. And when Energy Saver puts the display to sleep, elecricity usage drops to 3.6W.

This is an older monitor, not especially crisp, and slow to wake up, but it's a contender for use on a server, where it will only be powered on when necessary. The 1152 x 870 75 Hz setting is a good compromise between resolution and a steady display. (60 Hz tends to create a subtle flicker that can tire your eyes over time.)

Not bad for $3 - and I also got a free 15" 10-year-old Dell E550 at the same moving sale. It draws a whole lot less power - between 49 and 55 Watts in my various tests. Here's the quick overview:

800 x 600 @ 60 Hz, 49.4W; 75 Hz, 52.5W; 85 Hz, 54.8W
1024 x 768 @ 60 Hz, 51.6W
640 x 480 @ 60 Hz, 49.2W; 75 Hz, 50.6W; 85 Hz, 52W; 100 Hz, 54.2W

Interesting pattern: The higher the refresh rate and/or resolution, the greater the power draw - but not by a huge amount. There's only about 10% variance among the settings I tested.

This monitor also has one big plus over the Gateway Vivitron - the power button is up front, making it easier to turn it on and off. Thank goodness most displays moved away from rear-mounted power buttons years ago.

The third display I tested is an ancient Compaq 15" from the mid-to-late 90s. I picked up a few of these refurb at a very good price. They're not great monitors, but okay for setting up computers and testing. I was the same pattern in energy usage:

640 x 480 @ 60 Hz, 67W; 75 Hz, 71W
800 x 600 @ 60 Hz, 69W; 75 Hz, 74W
1024 x 768 @ 60 Hz, 73W

With Energy Saver putting the display to sleep, this drops to 14.5W - a lot more than the 17" Gateway Vivitron.

I next tested a 17" Micron display that my wife used to use with her Windows PC. No matter what resolution and refresh rate I chose, power draw was steady at between 118.5 and 119W. That surprised me after my other tests.

My stock CRT display for years has been a Samsumg 700DF, which supports up to 1280 x 1024 pixels. I've used it with my Titanium PowerBook and various G4 Power Macs, most recently with the dual 1 GHz Mirror Drive Door model. The display is crisp, but the refresh rate at 1280 x 1024 is a low 60 Hz. At tested resolutions and refresh rates, it consistently measured 120W.

By contrast, my 19" Dell flat panel display draws just 26W at its native 1280 x 1024 resolution. This is my primarly display - easy on the eyes, good resolution, and it sold for a great price when I bought it many years ago.

You can save quite a bit of energy by choosing the right display. The flat panel beats the CRTs hands down, the 15" Dell CRT draws about 30% less than the even older Compaq, and the Gateway Vivitron saves 20-25% over the Samsung and Micron monitors I tested.

End result: Until I can afford a new flat panel display, I'll keep the 19" Dell flat panel as my primary display on my Leopard machine (1.6 GHz dual G4 upgraded Digital Audio Power Mac), the Samsung on my Mirror Drive Door (the Gatewaw draws less power, but it's not crisp, wakes from sleep slowly, and has poorer color). On my server, I'm going to hook up the 15" Dell E550, which uses less energy than any of the CRT displays I've yet tested. I'll run it at 1024 x 768, which is lower than I prefer, but then I'm really only using this dual 500 MHz Power Mac G4 as a servery, so it's not a big deal.

Number Crunching

Electical rates range from 12¢ to 15¢ per killowatt-hour here in Michigan. By using a flat panel display instead of a 17" CRT, I save between 69 and 94 Watts - say an average of 85. That's roughly 2.04 kWH per day, 61 per month, for a saving of $7.30 to $9.20 a month, ignoring things like sleep mode and Energy Saver settings.

But you probably don't run your monitor 24/7. Let's say you have your monitor on 8 hours a day, 5 days a week, and you're using it enough so sleep mode rarely kicks in. 22 workdays in a month times 0.68 kWH per day comes out to 14.96 kWH per month. Savings: $1.80 to $2.25 per month in this scenario - $22 to $27 a year.

Ballpark figure: If you're using a 17" CRT and replace it with a 19" to 22" flat panel display, you may reduce your electric bill $20 a year assuming a 40 hour work week - or  $100 assuming the display is on 24/7. Use that display for 5 years, and you've saved between $100 and $500, probably enough to justify that $99 flat panel display Dell had on clearance last week or that $160 22" 1080 x 1920 display you discovered on dealmac.

Other benefits of going flat panel: No flicker, so it's easier on the eyes, and crisp pixels, where CRTs can become fuzzy over time. Less heat. And you'll have all those extra pixels to play with if you go widescreen. I find a 1080 x 1920 display very tempting, as I often have a dozen or more apps active at once, lots of overlapping windows, and the extra screen width would be a real blessing. (I've tried 1440 x 900 displays. After years at 1280 x 1024, I miss the extra height. Going to 1080 makes things even better.)

You'll need to do your own number crunching for your display, the new one you're looking at, monthly usage, and your local electrical rate. Just be sure to do your due diligence before you buy a new monitor - find out what reviewers and end users have to say about things like color accuracy, glare, build quality, etc.