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?
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:
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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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
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?
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.
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.
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.