For one hour on March 31, 2007, 2.2 million residents and 2,100 businesses in Sydney, Australia turned off their lights for the first-ever Earth Hour, which was developed to promote awareness about energy conservation. In 2008, more than 20 cities worldwide, including San Francisco, Toronto, Sydney, Chicago, Dublin and Atlanta, have signed up to participate in Earth Hour, and will make the same effort to power down their lights between 8 and 9 pm on March 29.

Earth Hour is working to educate people on energy conservation, not just for one day, but in everyday life as well. Even the impact of one night can make a difference: the organization’s website claims that if the greenhouse reduction achieved in the Sydney Central Business District during Earth Hour was sustained for a year, it would be equivalent to taking 48,616 cars off the road for that year.

So what can you do to conserve energy in your own home? An obvious answer is to switch off the lights in every room when you’re not using them (a surefire way to save money on your electricity bill, too). But there’s another option that you may not be aware of: switching out all of your incandescent bulbs for energy-efficient light bulbs.

According to the Energy Star website, if every American home replaced just one light bulb with an Energy Star qualified bulb, it would save enough energy to light more than 3 million homes for a year, offset over $600 million in annual energy costs and prevent greenhouse gases equivalent to the emissions of more than 800,000 cars. That’s quite a bit of savings for changing just one light bulb.

Look for compact fluorescent Lightbulbs (CFLs), which are now widely available and sold in many shapes and sizes, for use in your fixtures. They may be a little bit more expensive, but according to Treehugger, they’ll pay for themselves after about 500 hours of use since they last up to 15 times as long as incandescent bulbs. Recent advances in the technology used in CFLs have resulted in a much softer, more natural light than that afforded by early versions, which leaves little excuse not to switch to these savvy light sources, which use 75 percent less energy than traditional bulbs, and save approximately $30 in electricity costs over their lifetime.

It’s easy to switch out your bulbs: just look for a CFL that has the same labeling as the incandescent bulb you’re replacing. It should be right on the package. If you’re using a dimmer or three-way fixture, make sure to pick up a replacement made for that purpose. And, due to the small amounts of mercury contained within the CFLs, do your homework about how to safely dispose of the bulbs when they do burn out. Safe recycling is a must.