This year's Earth Hour - taking place on March 29th (Saturday!) from 8-9 pm local time. Nearly 200 cities spanning the globe and millions of individuals and businesses (form mom-and-pop joints to multinational corporations) have pledged to take part by turning out their lights for this symbolic hour. Organizer, World Wildlife Fund is encouraging people to use the time to engage in eco-friendly activities.

From candlelight dinners in San Francisco to glow-in-the-dark ultimate frisbee at the Illinois Institute of Technology, it's a time to get eco-imaginative. To see how you can get involved, visit earthhour.org.