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Do you want to show you care about energy conservation? Simply switch off your lights on March 28 from 8:30 to 9:30 p.m., local time.

This is Earth Hour, and Saturday is the third annual worldwide event. Earth Hour is both a symbolic act and the start of a practical habit.

Millions of homes and businesses and hundreds of major landmarks will go dark for one hour to show that energy conservation is imporant and to send this message to political leaders attending the United Nations Climate Change Conference in December 2009.

At the same time, Earth Hour reminds each of us how easy it is to conserve -- just turn off non-essential lights and electronics to reduce our own power consumption.

Lighting accounts for about 11 percent of a typical American home's energy bills, while computers and electronics add another 9 percent. So by shutting off these things when we're not using them, we can lower our load significantly.

Get into the habit this weekend with one hour in the dark. Make it fun by having dinner by candlelight, taking a stroll under the stars, or playing card games by a fire. The Daily Green has a few entertaining ideas for consenting adults too.

Earth Hour started in Australia and is sponsored by the World Wildlife Fund. Anyone can participate -- check out the website for details. At last count, 2,400 cities across 82 countries have officially signed up. 195 of these cities are in the United States.

Some famous buildings will be going dark on Saturday including: The Empire State Building in New York City, the Eiffel Tower in Paris, the St. Louis Gateway Arch, the Sydney Opera House, the Sears Tower in Chicago, Seattle's Space Needle, the Great Pyramids and Sphinx in Egypt, the Golden Gate Bridge in San Francisco, and Broadway theater marquees in New York City.

Even the flashy Las Vegas Strip will turn dark for an hour. Of course, the slot machines inside casinos will stay on, but almost all of the buildings and marquees on the Strip itself will be dark during Earth Hour.

For the very first time, the famous "Welcome to Las Vegas" sign will go off. Spokespeople say that Vegas lights have dimmed for a minute when a local celebrity dies, but the Strip and the sign have never gone dark for a full hour.

Other businesses are flicking the switch too. The golden arches at McDonald's in New Zealand and Canada will go dark, saving more than 10,000 kilowatt-hours for our neighbor to the north. The Canadian chain says it has also saved 3.1 million kilowatt-hours of energy through improved lighting, heating, and ventilation.

Both Nashville and Los Angeles are U.S. sponsor cities, so the Nashville Predators and the L.A. Kings hockey teams agreed to reschedule their game in Nashville to 5 p.m. The game should end around 7:30 p.m. with plenty of time for the arena to turn off the lights.

Blackberry addicts can log on before Earth Hour to a special website from Research in Motion. The company is encouraging fans of the mobile device to log-off for an hour and enjoy the silence.

You can even download a free iPhone game to remind you -- in advance -- to turn off the lights on Saturday. Anything to get the idea across, right?

Auto insurance company Esurance will offset your car's CO2 emissions at no extra cost if you buy an auto policy before Earth Hour. Of course, the kindest thing you can do for the planet is to drive less often.