I'm constantly being told that the simplest way to improve my green cred is to start using compact fluorescent lights. Yet some naysayers—like one of your Slate colleagues —argue that the environmental benefits of CFLs are negated by their mercury content. Who's right?
The case against CFLs is built largely on half-truths and innuendo. Yes, the energy-saving bulbs contain mercury, a neurotoxin responsible for a tremendous amount of human suffering over the years. And safely recycling CFLs remains far more difficult than it should be. But these facts don't justify sticking with inefficient incandescent technology that has barely changed since the invention of the tungsten filament nearly a century ago.
CFLs are lauded by environmentalists because they require far less electrical power than their incandescent counterparts. A 26-watt CFL bulb produces the same lumens as a 100-watt incandescent bulb. Assuming that you keep one of those bulbs aglow for six hours a day, switching to a CFL will save you 126 kilowatt-hours of electricity per year, which translates to 170 pounds of carbon dioxide emissions on average. Now, how many bulbs do you have in your house? Twenty? Thirty? Replace them all and you could conceivably (assuming six-hour-a-day use throughout the building) reduce your annual CO2 output by upward of 2.3 metric tons—about 10 percent of the average American household's annual carbon footprint.
Just look at what's forecast for Australia, which last year became the first nation to mandate a gradual phase-out of incandescent bulbs. According to Australia's Environment Minister, the measure will eventually slash the country's greenhouse gas emissions by 4 million metric tons per year—the equivalent of taking 1 million vehicles off the road.
But what about the mercury? The toxic heavy metal is integral to the design of current CFL bulbs: Electricity agitates the mercury molecules, causing them to emit ultraviolet light. That light then spurs a bulb's phosphor coating to give off visible light. But the amount contained in each bulb is barely enough to cover the tip of a ballpoint pen, and won't cause any bodily harm as long as simple precautions are taken. The National Electrical Manufacturers Association has voluntarily imposed a limit of 5 milligrams per bulb on all CFLs sold in the United States—about 1 percent of the mercury contained in an old home thermometer. Since manufacturers are well aware that health fears are preventing the widespread adoption of CFLs, most have committed to making bulbs with even less mercury than NEMA's standard. The average CFL bulb now contains around 4 milligrams of mercury, and that figure should drop closer to 2 milligrams in the very near future. Much of the credit for these reductions goes to Wal-Mart, which has pressured GE, Royal Phillips, and Osram Sylvania to cut down on the quicksilver.
The irony of CFLs is that they actually reduce overall mercury emissions in the long run. Despite recent improvements in the industry's technology, the burning of coal to produce electricity emits roughly 0.023 milligrams of mercury per kilowatt-hour. Over a year, then, using a 26-watt CFL in the average American home (where half of the electricity comes from coal) will result in the emission of 0.66 milligrams of mercury. For 100-watt incandescent bulbs, which produce the identical amount of light, the figure is 2.52 milligrams.