World Wildlife Fund’s Earth Hour’s a now 4-year-old annual event when everyone’s encouraged to turn off their lights for an hour. In 2010, Earth Hour will be happening from 8:30 pm – 9:30 pm (your local time) this Saturday, March 27.
To participate, turn off your lights at 8:30 PM for one hour local time. That's all. There are no hard and fast rules.
I happen to live in Las Vegas, a city known for it's flashy lights. Will Vegas join in? Yep, it will. Most of the hotels, casinos and attractions on the Las Vegas Strip will turn off most of their lights for that hour.