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CFL’s Energy Saving Questions In the May 2007 issue of Popular Mechanics, they tested seven popular compact fluorescent light bulbs (CFLs) and found that the light quality in all of them topped that emitted by traditional incandescent bulbs. Following that lab test, we received a lot of questions from readers regarding the environmental impact of the mercury contained in CFLs. For more of the lowdown on these energy-saving bulbs, we crunched the numbers and checked in with the Department of Energy and Russ Leslie at Rensselaer Polytechnic Institute. —Julianne Pepitone and Emily Masamitsu. How do CFLs and incandescents compare in terms of electricity consumption? On average, CFLs require about 25 percent of the electricity as their incandescent counterparts to produce equivalent light. Replacing an incandescent with a CFL ultimately decreases the amount of electricity the nation’s power plants must generate and, in turn, the amount of carbon dioxide—a powerful greenhouse gas—that they emit into the atmosphere. Saving energy equals saving the enviroment. Why are incandescents less efficient than CFLs? Unlike compact fluorescents, incandescent bulbs produce light by heating the metal filament inside the bulb and thus do not help in saving energy. When electricity passes through the filament, its temperature rises to 2,300 degrees Celsius, with the heat causing the filament to glow white-hot and emit light. But only 5 to 10 percent of that electricity is transformed into visible light. “In an incandescent bulb, much of the electricity is used for heat, which is not efficient,” Leslie says. “Fluorescent lights use electricity to do much more than heat a solid object.” How much of a difference can CFLs really make? According to EnergyStar—a program run by the Environmental Protection Agency—if each U.S. home replaced just one of its incandescent bulbs with a CFL, the electricity saved each year could light 3 million homes and prevent greenhouse gas emissions equal to that of 800,000 cars. And with a recent study for the U.S. government saying that a single 24-watt CFL’s lifetime energy savings add up to the gas equivalent of a coast-to-coast Prius road trip, it’s probably time to get moving on your energy footprint.