Turn off your lights!
In 2009, According to the Earth Hour website, more than 4,000 cities in 87 countries went dark. Here in the United States, and estimated 80 million Americans participated, along with 318 cities and 8 US states.
I enjoyed spinning by candlelight so much that I just left the lights off for the night. I am not sure Scott noticed much difference because his usual source of light is his laptop anyway 🙂