In the May 2007 issue of Popular Mechanics, we 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
Why do CFLs require mercury to produce light?
Compact fluorescent bulbs are made of glass tubes filled with gas and a small amount of mercury. CFLs produce light when the mercury molecules are excited by electricity running between two electrodes in the base of the bulb. The mercury emits ultraviolet light, which in turn excites the tube’s phosphor coating, leading it to emit visible light.
How much mercury is contained in a CFL?
Each bulb contains an average of 5 milligrams of mercury, “which is just enough to cover a ballpoint pen tip,” says Leslie, associate director of the Lighting Research Center at Rensselaer. “Though it’s nothing to laugh at, unless you wipe up mercury [without gloves] and then lick your hand, you’re probably going to be okay.”
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.
How much mercury do power plants emit to light a CFL?