Earth Hour is a worldwide grassroots movement uniting people to protect the planet, and is organised by WWF. Engaging a massive mainstream community on a broad range of environmental issues, Earth Hour was famously started as a lights-off event in Sydney, Australia in 2007. Since then it has grown to engage more than 700 cities and towns worldwide, and the one-hour event continues to remain the key driver of the now larger movement.
Visit the Earth Hour website for more info.