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If every Chicago resident replaced one light bulb with a compact fluorescent bulb, it would reduce greenhouse gas emissions by the equivalent of more than 20,000 cars, according to the city's Department of Environment. If every home in the country did the same, it would be like ditching 800,000 cars and would save enough energy to light more than 2.5 million homes for a year, according to Energy Star, a joint program between the EPA and the U.S. Department of Energy.

CFL's, which use 75% less energy than incandescent bulbs and last up to 10 times longer, cost a few bucks more that regular bulbs but save you $30 in energy costs over each bulb's lifetime, according to Energy Star.