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Asus Power Draw

CCFL Versus LED: Is There A Downside To Going Green?

Let’s start by examining our Asus trio. To be honest, this article began many months ago with some considerable dialog between Asus and ourselves. The two MS-series monitors were the first units we tested, and it was with them that we devised our first power testing methodology.

Black and white screen tests are pretty self-explanatory; we used an empty MS Word 2003 document at full-screen with no toolbars showing to create the white display while full-screen back was done by having a Windows screen saver show only 100% black. For video testing, we ran a two-minute clip from “Sherlock Holmes” and took the average power draw value as measured by a Belkin Conserve energy monitor sitting between the display and the wall.

Monitor Test
Asus MS238H
Asus MS246H
Asus VW246
Blank screen saver
29.3 W
29.9 W
44.8 W
Video, 100% brightness
28.9 W
29.0 W
44.8 W
Video, 75% brightness
25.6 W
25.4 W
38.5 W
Video, 50% brightness
22.3 W
22.3 W
32.1 W
White, 100% brightness
27.7 W
27.2 W
43.8 W
White, 75% brightness
24.4 W
23.7 W
38.1 W
White, 50% brightness
21.2 W
20.6 W
31.4 W
Black, 100% brightness
28.9 W
29.1 W
44.3 W
Black, 75% brightness
25.6 W
25.6 W
38.4 W
Black, 50% brightness
22.4 W
22.5 W
32.0 W

The first thing that jumps out here is that the two MS models live up to their spec sheets’ promises of similar power consumption. Even if the vendor spec of a 33 W maximum proved pessimistic, the differences in draw in all of our scenarios are effectively nil. Yet one uses LED backlighting and the other CCFL. Huh?

We immediately sent these early results back to Asus' team, which reported that “the product manager is quite surprised also.” We suspected that the power circuitry must be the actual determiner of power consumption, and not the backlight technology. Further inquiry yielded this official reply: “Actually, [the product manager] was surprised that nobody had asked the question before now. Yes, the MS series uses the same electronics regardless of panel type, so their base energy consumption numbers will be the same.”

This bombshell was validated when we received the VW246 and confirmed that it indeed sucked down roughly 50% more energy than its CCFL-based cousin.

As for power numbers, another interesting point leaped off the spreadsheet. In retrospect, we should have guessed it all along, but so many years of using CRTs caused us never to question the assumption that black was better. Black saved energy. That’s why we have (yup, still running) for all those users who have Google Search as their home page. But in the LCD world, where LCD matrices must apply voltage in order to twist the crystals within a panel cell in order to block the backlight from shining through, black is bad. Black wastes energy. This is why a screen showing HD video usually consumes less energy than the same screen sitting at a black Windows desktop. Often, the most energy inefficient thing you can do is run a blank screen saver, that old power-saving standby from the CRT era. Things change.

As you can see, there’s a significant difference—30% to 40%—between running a screen at 100% brightness versus 50%. If you reach out to your display right now and dial back the brightness from 100% to 50%, it’ll probably look very gray and muddy to you. Most of us have become accustomed to 100% brightness, but that’s actually a lot like letting your car engine idle at higher RPMs. In reality, you’re not going to drive any faster; you’re just wasting gas.

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