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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?

Sklivvz
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    AFAIK a black screen will use *more energy!* This is due to the fact that LCD monitors are [uniformly backlit](http://en.wikipedia.org/wiki/Liquid_crystal_display#Illumination), 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 07 '11 at 23:08
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    @fredley: you should write up an answer -- another [SOURCE](http://www.scientificamerican.com/article.cfm?id=fact-or-fiction-black-is) that confirms your answer (assuming the question is about LCD and not CRT). You should get the credit for it. – Hendy Jun 07 '11 at 23:22
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    @fredley I second @Hendy you should turn it into an answer. –  Jun 07 '11 at 23:43
  • Could a little bit of red colouring be better than black (for searching with Google like a "Proud Canadian")? http://www.searchbin.ca/ – Randolf Richardson Jun 08 '11 at 06:36
  • There's some good answers on this for mobile devices [here](http://android.stackexchange.com/questions/5043/do-bright-wallpapers-spend-more-battery-than-dark-ones). – dpatchery Jun 08 '11 at 11:44
  • With modern LED screens the backlite actually turns off for large dark areas of the screen, so black screen has potential to save energy at least in theory on modern LCD LED displays. – Ma99uS Jun 08 '11 at 13:46
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    @Ma99us: [Citation needed] (In other words, I don't believe you) – Lennart Regebro Jun 08 '11 at 16:48
  • @Lennart: Have you searched for LED LCD? Specifically Full-Array LED backlight LCD, like the 47LG90. They have an array of more than a thousand LEDs that can be dimmed by areas. – André Paramés Jun 08 '11 at 22:35
  • @André: Yes I have, but I searched for displays, not TV's. Although this technoogy does exist, it is only for TV's which makes them kinda moot for web-pages. :) The reason for that is that it only makes sense on TV's, which is the original reason for my skepticism. A computer screen that did this wouldn't be very good. :) – Lennart Regebro Jun 09 '11 at 04:54
  • @Lennart: I object to your use of [Citation needed] to imply that you don't believe a claim. We should of course expect the same skeptic rigour to significant claims that we find agreeable :) – David Hedlund Jun 09 '11 at 08:10
  • @Lennart - I'm puzzled by "A computer screen that did this wouldn't be very good." I understand that they just don't seem to be available right now, and most monitors probably display less black than a television, but they should still benefit in power savings (as well as improved contrast ratio, the other reason to selectively dim). A related example - OLED displays achieve the same result in a different manner and have been very beneficial to smartphone displays. – Saiboogu Jun 10 '11 at 16:25
  • @Saiboogu: Turning off the backlight for dark areas makes for higher contrast, but you loose the detail, as you no longer can make out the differences and might even loose detail like bright dots in the dark areas. That is acceptable on a TV, but not on a computer screen. OLED's are something entirely different. – Lennart Regebro Jun 10 '11 at 21:22
  • I wonder if this would make any noticable difference to people's battery life on their phone? Is enough energy saved to become noticable over short periods of time? – user3453 Jun 09 '11 at 14:20
  • @Lennart - You're assuming a very poor design in the backlight logic. I see no reason for this - it only makes sense to turn off the backlight when no light is required in an area. If a bright point is displayed in the dark area, you keep the backlight on at that location. – Saiboogu Jun 11 '11 at 13:50
  • @Saiboogu: Then you can never turn off the backlight except for when the whole of the screen is completely black. Thereby defeating the purpose of it. This technique gives higher contrast at the expense of detail. See Wikipedia. Sorry. – Lennart Regebro Jun 11 '11 at 15:16
  • @Lennart - I think you're misunderstanding what I'm talking about. There are LCD TVs that can turn off the backlight in small zones, when there is no light required in that area. Or dim it, if the area just isn't supposed to be as bright. It sounded like you said such a thing wouldn't work for PC displays - it would work the in the same way, and still be beneficial. I'm not talking about turning the entire backlight on and off, just an area. – Saiboogu Jun 11 '11 at 16:00
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    @Saiboogu: Exactly. I'm saying that wouldn't work for PC displays, because it means you lose small differences in the dark color and lose any bright spots. You then say "only turn it off when all the pixels in the area are completely black". I'm then pointing out that this is *never*, and even if you do it you would get one area where black is black (because the backlight is off) and the adjacent area black would look gray (because it's on). These types of effects are unacceptable in a computer monitor. This is now the third time I say this, repeating it more time is hardly going to help. – Lennart Regebro Jun 11 '11 at 16:22
  • @Lennart Guess we'll have to agree to disagree. I only drug it out another round because I thought you misunderstood what I was saying, apologies for that. – Saiboogu Jun 12 '11 at 15:18
  • @Saiboogu: No problems. And its not a problem about disagreeing, it's just you who don't understand how this would make a computer screen look and behave. Ask yourself: Why is it only TV's that has this technology? My MacBook have LED backlight. Why don't Apple turn them off? Don't you think they would if they could, to prolong battery life? – Lennart Regebro Jun 12 '11 at 16:41
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    From the site: "We believe that there is value in the concept because even if the energy savings are small, they all add up. Secondly we feel that seeing Blackle every time we load our web browser reminds us that we need to keep taking small steps to save energy." -- seems like a rather desperate interpretation of statistics... – Rei Miyasaka Jul 31 '11 at 09:23
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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 08 '11 at 07:47
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    Yes, a black background will save energy on newer display technologies such as [OLED](http://en.wikipedia.org/wiki/Organic_light-emitting_diode#Advantages). > An inactive OLED element does not > produce light or consume power **more black = less power** Also, some LCD displays have LED local backlight dimming which can lower power consumption but only with large solid black areas. – JarrettV Jun 08 '11 at 07:47
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    See also [this question](http://electronics.stackexchange.com/q/30541) and especially [this answer](http://electronics.stackexchange.com/a/32018) 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
  • They save the energy by causing visitors' eyes to hurt, and therefore poor visitors have to stop using their computer earlier — that's power saving. – Display Name Oct 01 '15 at 18:19
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    Might not a good answer also consider the costs (if any) of acting as a proxy search server, such as extra communication? It might also consider the ticker (“6,512,617.474 Watt hours saved”) on the Blackle screen, which is either faked or does extra communication. I seem to remember there is controversy about whether answers should treat implicit assumptions. – PJTraill Nov 05 '17 at 14:50
  • I agree with PJTraill, Blackle will definitely use more energy if set as browser start page than using a blank tab. With a start page set, every time you open the browser, you will send a request over the internet to fetch this page, involving many routers and servers wich use a lot of power. Save energy by setting a blank tab. Also, don't be lazy, enter `youtube.com` in the address bar instead of googling for `yt` and clicking the search result. Every Google search uses about 0.0003 kWh. – Georg Patscheider Jul 19 '19 at 07:09
  • As of 2021, the claim in the [Blackle FAQ](http://www.blackle.com/faq/) reads as follows: *There are significant energy savings on black websites for LED backlit LCD, OLED and CRT monitors. CCFL backlit LCD screens are not significantly affected by display color because of their constant backlight. Since 2005 manufacturers have moved away from these CCFL backlit screens. In 2021 the majority of monitor sales are LED backlit LCD's.* – gerrit Nov 18 '21 at 16:48

4 Answers4

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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.

Oddthinking
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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 08 '11 at 02:03
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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 08 '11 at 02:16
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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 08 '11 at 02:53
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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 08 '11 at 03:04
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    btw - we pay a lot more for fuel & electricity here in UK than in the US, so that may affect our thinking on energy use. – FumbleFingers Jun 08 '11 at 03:05
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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: http://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 08 '11 at 03:51
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    Some newer LCDs have backlight control based on overall picture level, and some of those can control backlight in sections. Edge-lit and segment-lit LED based LCDs take much less power on darker screens. These are mainly found on big home cinema screens, though, and very rare in consumer desktops screens. Even if there was a saving, there's almost nobody who would benefit. – John Ripley Jun 08 '11 at 07:56
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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 08 '11 at 21:14
  • I prefer this answer to the accepted one for a couple of reasons. This answer illustrates that most of us (including my first impressions) were persecuting a straw man. As in, blackle *already knew* this answer was **No** for LCDs. I also appreciate that it gives credit to blackle for not perpetuating a myth. I love the data of the above questions, and they actually show that blackle's "negligible" results may be outdated, but this answer provides everything I think is needed to answer the questions -- the rest just supplement it very nicely. – Hendy Jun 10 '11 at 20:21
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    Using a Kill-a-Watt on my older 24" LCD display, a completely black screen at full brightness sometimes registered 1W less than a completely white screen, but turning down the brightness just a little bit saved 10W. I haven't tested with my newer 23" LED display. – geerlingguy Mar 17 '13 at 15:52
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    I would be interesting to see what are the results for OLED screens. – vartec Feb 13 '14 at 14:37
  • *"As regards the environmental/economic issue, you can pretty much ignore that - if you average everything out, they become the same thing."* This is a very smart observation. And it would be true if we factored in pollution in our taxes. Unfortunately we still often don't do that. IMHO it should be politics goal to make sure that the two become the same. More pollution => more taxes, so in the end the cheaper product will always be the 'cleaner' one. At the moment this still often isn't the case though. *EDIT sorry, old post but today is in sidebar for some reason.* – Stijn de Witt Nov 03 '17 at 20:48
  • Is there any chance of you updating this to take account of newer technology, in particular (AM)OLED? I should also appreciate an initial summary and a table of effects by technology as a courtesy to readers, but perhaps that is asking a bit much! – PJTraill Nov 27 '18 at 10:27
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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

TFD
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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 04:53
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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
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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.

Alenanno
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user3471
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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

Hellreaver
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