Plan your cocktail party by candlelight now — for Earth Hour 2009. World Wildlife Fund, the world’s largest conservation organization, is planning the world’s biggest lights-out on March 28, 2009 from 8:30 pm - 9:30 pm.

Earth Hour started in 2007, with the people in Sydney, Australia turning out their lights as a show of support for action on climate change. Then in 2008, 50 million+ people in 400 cities participated. For 2009, 74 cities in 62 countries — including big U.S. cities like Chicago, Las Vegas, Los Angeles, and Miami — have already signed up to go dark for an hour.

Of course, the hour alone should save some energy — and the carbon emissions that would’ve been created producing it. But the goal of Earth Hour, according to WWF, “goes far beyond the initial 60 minutes of awareness, contributing to substantial, long-term action against climate change.”

Want to be part of the power out? You can sign up to take part as an individual — or think bigger and get your whole city or town involved (PDF)! Below’s a video about the Earth Hour effort to inspire you to take action.