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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, 2011 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, 2011 at 23:22
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    @fredley I second @Hendy you should turn it into an answer.
    – user1936
    Jun 7, 2011 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, 2011 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, 2012 at 13:54

4 Answers 4

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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, 2011 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, 2011 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, 2011 at 2:53
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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, 2011 at 3:51
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    @Oddthinking: As it happens I got my scientist brother to do the sums for me this afternoon, and I now agree I was a bit overoptimistic. I work (and live) at home, so my screen is on a lot more than most, but yes - I won't actually have saved money yet (though I will be up on the deal in 2-3 years, for sure). As regards the environmental/economic issue, you can pretty much ignore that - if you average everything out, they become the same thing. Except, as noted, lower US energy taxes do tend to distort the situation there.
    – FumbleFingers
    Jun 8, 2011 at 21:14
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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, 2012 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, 2012 at 17:31
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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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On amoled (active-matrix organic light-emitting diode) screen types, such as the Galaxy s5, each pixel is individually lit when powered, so using pitch black backgrounds theoretically reduces power draw marginally.
Sources: AMOLED displays
Galaxy s5 specs

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  • Do you have any sources for this?
    – drat
    Dec 17, 2015 at 8:03
  • @drat added specs for the s5 and a link describing amoled screens
    – Hellreaver
    Dec 17, 2015 at 8:09
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    Upvoted because newer technology is neglected in other answers, but I think your answer ought to include the relevant information from the sources you cite.
    – PJTraill
    Nov 27, 2018 at 10:23

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