The principle behind Blackle is based on the fact that the display of different colours consumes different amounts of energy on computer monitors.[3] The creators of Blackle cite a 2002 study from Roberson, who tested a variety of CRT and LCD monitors and found that an all black screen consumed less energy than an all white screen on all of them.[3]
The creators of Blackle state that the idea behind the site came from a blog, which estimated that a black Google would save 750 megawatt-hours a year[1]. On the Blackle homepage,
the creators of Blackle provide a count of the number of watt-hours
that they claim the users of Blackle have collectively saved.
http://http://www.blackle.com/
