The Earth Policy Institute states that once the whole world shift entirely to compact fluorescent light bulbs, we would be able to shut down 270 coal-fired power plants. Also, the gasoline equivalent of the energy that would be saved by replacing a 100W incandescent bulb with a 24W CFL is enough to drive a Toyota Prius from New York to San Francisco. Therefore, the two-fold benefit of swapping your bulbs are 1) it can save a lot of energy, and 2) can save you a ton of money, as well.