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Blackle is a search engine that claims to save energy because it uses a black background. Is there any evidence to back up their claim that a website using a black background will save energy, and if so, how much energy will be saved?

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AFAIK a black screen will use more energy! This is due to the fact that LCD monitors are uniformly backlit, and power is used to activate the LCD crystals to block out the light -> more power is used to block out more light -> a black screen uses more energy! –  fredley Jun 7 '11 at 23:08
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@fredley: you should write up an answer -- another SOURCE that confirms your answer (assuming the question is about LCD and not CRT). You should get the credit for it. –  Hendy Jun 7 '11 at 23:22
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@fredley I second @Hendy you should turn it into an answer. –  Christofian Jun 7 '11 at 23:43
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Another thing to consider is OLED screens. These are starting to appear in more mobile devices and will (probably) start becoming more mainstream soon. These displays don't have a backlight - each pixel is a light source in its own right. For these screens, a black background will make a significant difference to the amount of power consumed. –  Chris Roberts Jun 8 '11 at 7:47
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See also this question and especially this answer on Electrical Engineering for some experimental (aka original research) and theoretical (perhaps not 'written for laymen') answers to the question. –  Kevin Vermeer May 16 '12 at 13:54

4 Answers 4

Blackle actually cite a real reference to backup their claims. Credit to them!

On their About page they quote a line from a Energy Use and Power Levels in New Monitors and Personal Computers, Roberson et al, Environmental Energy Technologies Division, Ernest Orlando Lawrence Berkeley National Laboratory, UCLA.

The quote is:

"Image displayed is primarily a function of the user's color settings and desktop graphics, as well as the color and size of open application windows; a given monitor requires more power to display a white (or light) screen than a black (or dark) screen."

That line does actually appear in the report, and is backed by the following data:

Table 8 from report

The reports goes on to conclude:

Among the few LCD monitors in the table, the power used to display a white screen is indistinguishable from power used to display the desktop. Thus, it appears that display color is a significant determinant of on power for CRTs, but not for LCDs.

Clearly, in LCD technology terms, 2002 is a long time ago. I have no knowledge of any power-saving innovations in the meantime.

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Nice answer -- I find it odd that other sources are stating that LCDs should use more power for black while the chart above is showing them using [negligibly] less. Still, nice digging, and that last quote jives with what others have been finding as well. –  Hendy Jun 8 '11 at 2:03
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I find it odd that anyone remotely interested in saving energy would waste their time and ours considering the performance of CRT technology. For the good of the planet, chuck that old screen out! –  FumbleFingers Jun 8 '11 at 2:16
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@FumbleFingers, first, both Blackle and this report are coming from the turn of the century, when CRT was still king. Second, in order to justify throwing out an existing CRT monitor for ecological reasons, you have to show that the total power it will consume over its life is more than the total energy consumed by an LCD screen INCLUDING its manufacture (pro-rated for expected lifetimes), which is a big claim. That doesn't even factor in non-energy related pollution. –  Oddthinking Jun 8 '11 at 2:53
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@Oddthinking: Well, someone else can do the sums. The company I worked for 7-8 years ago weren't known for being profligate, but they allowed staff to buy all their CRT screens for buttons, and replaced them with LCDs. A year or two later I gave away the 21" CRT I'd paid £20 for, and even though it cost me over £200 for the LCD replacement, I'm still using it now. And I bet I've saved money. –  FumbleFingers Jun 8 '11 at 3:04
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@FumbleFingers, "I bet I've saved money." I would certainly consider taking that bet. There are a lot of factors to consider here in your calculation, but the payback period is quite long. (e.g. for a starting point: answers.google.com/answers/threadview?id=1082). That is just economic, not environmental considerations (which I strongly suspect discourage replacement, but I have no evidence.) –  Oddthinking Jun 8 '11 at 3:51

LCD panels make black pixels by blocking the colour filtered back-light from exiting the panel. It therefore uses a little more power to make black than to make white

See http://electronics.howstuffworks.com/lcd2.htm

LCD TV's sometimes have "dynamic contrast" LED back-lighting which should save power in black. This feature is sometimes found on high end IPS LCD monitors, though is useless for general computer use as the LED back-light resolution does not match the actual LCD resolution

OLED panels use power to make each individual coloured pixel, so black would save power. Who uses a couple of 24" OLED's yet?

See http://electronics.howstuffworks.com/oled2.htm

And more interestingly http://www.popsci.com/scitech/article/2009-09/mit-scientist-explains-oled-function-glowing-pickle

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I think it's the other way around. Most of the LCDs I've seen with dynamic contrast are crappy TN panels. Anyone who cares enough to pay for an IPS panel will turn off dynamic contrast even if it's available. –  Fake Name Mar 25 '12 at 4:53
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"useless for general computer use as the LED back-light resolution does not match the actual LCD resolution"? With dynamic contrast back-light is not dimmed per individual pixel, but most typically for whole screen. –  vartec Mar 25 '12 at 17:31

When blackle came out (2007) the majority of users still had CRT monitors. There's a nice discussion of this here http://ecoiron.blogspot.com/2007/08/history-in-january-2007-mark-ontkush.html

From the above link:


Criticisms There has been both praise and criticism for this initiative, with its supporters citing it as a great example of environmental thinking, and its detractors pointing out usability and aesthetic problems, as well as questions about the scientific validity of the claims. Some of the issues are listed below.

  • Since the technique is most effective on CRT monitors, some proxy sites have been criticized for not mentioning this fact. In particular, the Blackle site has been heavily criticized, as it is probable that they are generating an substantial Adsense revenue stream from implementing the concept.
  • CRT monitors are being phased out; about 75% of monitors in active use worldwide are LCDs. Additionally, countries with a high percentage of CRT are replacing them rapidly; for example, Display Search projects that only 18% of the monitors in China will be CRTs by the end of 2007. Therefore, although the technique would be effective for a limited period, it is questionable whether the disruption would be beneficial.
  • CRTs are generally darker than LCDs, and the text on many of the proxy sites is barely readable on monitors of this type. For example, Blackle uses a small grey font on an all black background. It is possible that these 'all black' proxy sites are only usable on LCD screens, and this would negate the energy savings.
  • Proxy sites cannot handle the heavy load that high volume sites are accustomed to. For example, on August 1st, 2007 and several prior occasions, the Blackle web server was producing intermittent error messages for extended periods of time.

So, already back in 2007, most people were questioning the usefulness for the black background web pages for saving energy.

If we were all still using CRT monitors then yes you could save a lot of energy by using the black backgrounds. But, this is 2011 and the few CRT monitors left in existence are sitting in the corner of our basements unplugged and waiting to be taken to the electronics recycling graveyard.

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Since the last answers to this question were posted, manufacturers have switched from CCFL to LED back-lighting, which works more like CRTs did. This means displaying black should be more efficient again.

http://en.wikipedia.org/wiki/Backlight

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This post does not cite any references or sources. Please help improve this post by adding citations to reliable sources. Unsourced material may be challenged and removed.

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Welcome to Skeptics! This is an answer based purely on a theoretical model. Please edit it to add references to empirical data to support your claim that it "should be more efficient". –  Oddthinking Apr 18 at 20:58

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