The Google homepage switched “off the lights” and went black for one hour for all Google.com visitors in San Francisco as part of the Lights Out San Francisco Initiative to save energy for one hour today.
Lights Out San Francisco Initiative, a citywide energy conservation event on Oct. 20, 2007 when they invite the entire city of San Francisco to install one compact fluorescent light bulb (CFL) and turn off all non-essential lighting for one hour from 8:00 pm to 9:00 pm PDT!
Google expressed its support for the event and blacked out the homepage and posted the company’s commitment to environmental awareness and energy efficiency by supporting the Lights Out campaign
So why not have a black Google homepage forever? Blackle was an initiative which runs a black Google custom search based on this hypothesis, but Google clarified earlier that Black Google may not save energy after all.