Any truth in this? What do you think? If you think it's true I'll convert my blog to black.
I just received this email:
"When your screen is white - an empty word page, or the Google page, your computer consumes 74 watts, and when its black it consumes only 59 watts. Mark Ontkush wrote an article about the energy saving that would be achieved if Google had a black screen, taking in account the huge number of page views, according to his calculations, 750 mega watts/hour per year would be saved.
In response to this a black version of the Google search engine has been created, called Blackle, with the exact same functions as the white version, but with a lower energy consumption, check it out.www.blackle.com"
Wednesday, July 25
Black screen saves energy? Any truth
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6 replies:
It makes a superficial sort of sense. If you think about it a white object reflects all visible wavelengths of light, whereas a black one emits virtually none. So a monitor showing a black screen emits less as light than a monitor showing a white screen.
Witness how in a dark room with something light coloured on the screen, you can see just by the light provided by your monitor, that light energy's got to have come from somewhere.
The question is that if your monitor is not putting out white light, have you saved that energy, or is it just going elsewhere. The articles own figures claim quite a high proportion of energy is used by the monitor on things other than lighting up the screen white so it certainly sounds plausible.
However, it has to be said, it saves more energy to switch your compuer off when you don't use it, rather than just having the screen turn black.
The answer to this one is: it depends what type of screen you are viewing the site on. If you still have a CRT, then yes, you can make some savings by this method. If you have an LCD screen, however, as PCs increasingly do and all laptops do, then it makes next to no difference.
LCD screens have a constant backlight which is then selectively allowed to shine through coloured sub-pixels by a layer of liquid crystal, which can be made to polarize in different directions by applying a small voltage across it. Polarize in one direction, no light can get through. The other direction, all of it can.
The only relevant consideration for LCDs is therefore how often the polarization is required to change. Every change in colour of a pixel on the screen uses a briefly applied voltage to effect the change. The majority of websites using a white background, therefore, means that throwing in the occasional black background can probably only increase the usage of LCD screens.
Now, we know that today, 25% of screens are CRT, and presumably the vast majority of the rest are therefore LCD. So unless the savings you can make in CRTs are four times as large as the possible increase in power usage in LCDs (which it could well be), the answer is probably that white is fine for now.
Of course, if everyone could be persuaded to go black at once, then there might be an argument to be had, but since most people prefer the white background on aesthetic grounds, I don't see it happening.
Sorry for the extensive answer, but once I get going on technical things, I am hard to stop!
Things get more complicated when considering your readers rather than their energy consumption… The trouble with light text on a dark background is that it’s much more difficult to read for people with eye problems than the easier-on-the-eye black on white. So there’s not really an easy answer for the practical ethics of web design!
Its not correct in most cases - in fact with LCD screens the opposite may well be true.
Anyway, any savings are tiny and I'm sure they're outweighed by the power consumption of the blackle.com server...
You're much better off switching your computer off when not using it and saving your eyesight.
On a similar note if we all breathed less global warming would be solved...
I'm not a techie but agree that any savings would be minor and quite right that switching off would be a better shout.
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