Earth Hour will be celebrated tonight, from 8:30 to 9:30 p.m. local time, all around the world. People everywhere are being asked to turn off their lights for one hour to dramatize the link between global warming and energy use.

A spectator in space viewing Earth from its dark side would, ideally, see a rolling backout lasting a full 24 hours.

But you can do more than just turn out your lights. There are serious savings to be had from other simple sources, as well. For example…

A recent study commissioned by the Alliance to Save Energy revealed that U.S. companies could collectively save (US)$2.8 billion in energy costs every year just be turning off desktop computers that aren’t being used.

The study also suggests replacing old glass-tube monitors with energy-efficient LCD flatscreens and, where possible, replacing older desktop PCs completely, with laptops, to save energy.

Earth Hour started four years ago in Australia, which spans three time zones, and quickly spread around the world. In 2007, an estimated 2.2 million people participated. Last year, the figure is believed to have topped 50 million. This year, organizers are hoping a billion or more people will take part.