White power reduction

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Mr Evil
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White power reduction

Post by Mr Evil » Wed May 30, 2007 3:25 pm

I bought one of those nifty plug-in mains wattmeters, so I can test a few theories now. One of these is that since LCDs default to transparent when power is removed, that displaying a white screen will use less power than a black screen. That's the theory anyway, but lets see what the meter says:

The first test subject is an NEC LCD1770NX.

Code: Select all

Black screen: 24W
White screen: 23W
Interesting. How about an LG L1715S?

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Black screen: 26W
White screen: 25W
So there you go. It really works! It's not exactly a spectacular difference, but maybe it's enough to make lighter desktop backgrounds a little more attractive now.

Bigg
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Post by Bigg » Thu May 31, 2007 7:23 am

Yeah, somebody did a plugin to have a black google, and figured out how many tons of CO2 a year it would save if google made their own page black. I think that people should use whatever is comfortable for them. Don't use pure black on the background if you have a second monitor (without the taskbar), as you might forget to turn it off, thinking it is already off. I did that one day for a few hours, now I use the black dl.tv background, so that I know if the monitor is on.

Mr Evil
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Post by Mr Evil » Thu May 31, 2007 7:34 am

Bigg wrote:Yeah, somebody did a plugin to have a black google, and figured out how many tons of CO2 a year it would save if google made their own page black....
No, this is the other way around. Old CRT monitors may have used less power when displaying black, but LCD monitors use less when displaying white! Since you can hardly even buy CRT monitors anymore, the old way is now obsolete.

Bigg
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Post by Bigg » Thu May 31, 2007 9:30 am

So, basically, it just doesn't matter.

Mr Evil
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Post by Mr Evil » Thu May 31, 2007 10:30 am

A 1W difference is small, but it does exist. If your computer uses little power already, then it might be a difference that is worth thinking about, at least.

Lawrence Lee
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Post by Lawrence Lee » Thu May 31, 2007 10:37 am

Only CRTs use more power when displaying white.

fri2219
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Post by fri2219 » Thu May 31, 2007 10:50 am

The numbers posted are interesting, but are not distinguishable from randomly generated numbers, even at very low confidence levels. In order to be sure it actually makes a difference, you'd have to take samples from ~1200 LCD's. Even a modest increase in samples, like 100, could be enough, however.

Rusty075
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Post by Rusty075 » Thu May 31, 2007 1:03 pm

I would be willing to bet that world-wide there are still many more CRT monitors in use than there are LCD's.
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Bigg
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Post by Bigg » Thu May 31, 2007 3:26 pm

Rusty075 wrote:I would be willing to bet that world-wide there are still many more CRT monitors in use than there are LCD's.
Probably true, especially in other less affluent countries. I know my school has mostly CRTs. I have two CRTs in mainline service and one LCD, not counting a pair of laptops. I have a bunch more CRTs in secondary service in the basement for "testing" (playing with Linux or something).

frostedflakes
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Post by frostedflakes » Thu May 31, 2007 4:03 pm

Makes sense, LCD panels display color by blocking light. When the screen is white it isn't blocking any light, when black it's blocking all the light (technically not all, one of the weaknesses of LCD technology). :)

But the numbers do support the premise that the backlight is the biggest power consumer in the LCD. The actual LCD panel itself must consume next to nothing if the difference between fully blocking and not is less than a watt.
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Bigg
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Post by Bigg » Thu May 31, 2007 5:51 pm

frostedflakes wrote:Makes sense, LCD panels display color by blocking light. When the screen is white it isn't blocking any light, when black it's blocking all the light (technically not all, one of the weaknesses of LCD technology). :)

But the numbers do support the premise that the backlight is the biggest power consumer in the LCD. The actual LCD panel itself must consume next to nothing if the difference between fully blocking and not is less than a watt.
Hopefully that power will come way down with LED technology. :D

SoopahMan
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Post by SoopahMan » Sun Sep 16, 2007 9:02 pm

This is an important issue with LCDs. Do not use black screensavers - they aren't saving anything!

You do save 1watt, but much more importantly you preserve the life of the liquid crystals, leading you to not throw that monitor - or laptop - away as soon. That has a very significant savings to the environment. Plastics and poisonous metals staying out of the ground is a good thing. The energy required to manufacture your next monitor is also postponed, leading to less overall energy usage - by quite a bit - in your lifetime.

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