Google decided to be a part of the "Lights Out San Francisco" event that invites "the entire city of San Francisco to install one compact fluorescent light bulb (CFL) and turn off all lights for one hour, from 8:00 pm to 9:00 pm PDT" today, October 20. To promote this event, Google's homepage changes its background color from white to black. You should see the change during the day if you are in San Francisco.

"Given our company's commitment to environmental awareness and energy efficiency, we strongly support the Lights Out campaign, and have darkened our homepage today to help spread awareness of what we hope will be a highly successful citywide event," says Google in a page set up for the event.

Google also explains that, contrary to other opinions, permanently changing the background to black would not save energy. "To the contrary, on flat-panel monitors (already estimated to be 75% of the market), displaying black may actually increase energy usage."