After the Energy Independence and Security Act became law in late 2007, threatening an end to 40–100 watt general-service incandescent lamps, a consumer backlash began building against compact fluorescent lamps (CFLs). A common argument is that CFLs contain mercury, a toxic substance, whereas incandescent lamps don’t, countering the primary environmental benefit of using CFLs—significant reductions in greenhouse gas emissions at power plants.

The average CFL contains 4 milligrams (mg) of mercury, according to the National Electrical Manufacturers Association. This is after reductions following a voluntary commitment by NEMA’s lamp manufacturing members to cap mercury content at 5 mg for CFLs sold into the residential market that are rated less than 25W; 5 mg is just enough to cover the tip of a ballpoint pen. Some products have reached as low as 1.5 mg.

During use and disposal, some CFLs are certain to break and emit mercury into the environment. According to the Environmental Protection Agency (EPA), most of the mercury remains bound to the lamp if the bulb is broken, and the amount that escapes the lamp is still debated. Emission estimates vary broadly from 1.2 to 6.8 percent. This means if a CFL containing 4 mg of mercury is not recycled and breaks, 0.05–0.27 mg may be emitted.

So incandescents are better than CFLs when it comes to mercury emissions, right? Not so fast. A problem with this argument is that coal-fired power plants produce about one-half of all electricity in the United States and, according to the EPA, are the largest source of human-caused mercury emissions in the country—more than 50 tons in 2006. A portion of these emissions are airborne, oxidized and water-soluble; some mercury ends up deposited in the United States, while the rest enters the global cycle (more than half the mercury deposited in the United States, for example, originates at Asian factories). Mercury released into the air is the main way it gets into water; eating contaminated fish is subsequently the main way humans become exposed.

Because incandescent lamps consume three to four times more energy than a CFL, they cause more atmospheric mercury emissions at power plants that burn coal. According to EPA’s eGRID2006 (v.2.1), about 0.022 mg of mercury is emitted into the atmosphere per kilowatt-hour (kWh) of energy produced by coal-fired plants or 0.012 mg per kWh averaged across all power generation in the United States. A 75W incandescent operating over a period of 10,000 hours—the rated life of a competitive 18W CFL—will, therefore, generate an average 9.2 mg of atmospheric mercury emissions nationally, while the 18W CFL will generate 2.2 mg (plus possibly up to another 0.27 mg if the lamp is broken).

So CFLs produce less mercury nationally, right? Yes, while also slashing carbon emissions and providing substantial energy cost savings to their owners. But wait—what about states that don’t burn coal for power? What about differing quality and mercury content of coal and mercury control technologies at power plants? And what about mercury emitted during lamp production? Looking at the question at this level of detail would require intensive modeling, including a broad range of factors.

A team of Yale researchers recently did just that. Key assumptions included that each CFL contains 5 mg of mercury, 21 percent of spent lamps are recycled, 25 percent of the mercury in CFLs that is not recycled becomes atmospheric emissions due to breakage during transit, 3.5 percent of mercury entering landfills becomes atmospheric emissions, and CFL manufacturing produces slightly higher emissions per lamp but less overall due to longer average life.

The researchers concluded that replacing a common 60W incandescent with a 15W CFL typically yields net reductions in atmospheric mercury emissions ranging from 0.01 to 20 mg in the United States over 10,000 hours—but nominally not in states that use very little coal to make electricity: Alaska, California, Idaho, Maine, New Hampshire, Oregon, Rhode Island and Vermont. In these states, switching to a CFL actually can cause a small net gain in atmospheric mercury emissions—up to about 1.2 mg.

So are CFLs net producers of atmospheric mercury emissions? The answer depends on whether you are asking on a national, state or even utility level. As a national average, and in most states, switching from incandescent to CFL results in significant reductions in mercury and other harmful emissions. And this is really a national issue, and anything else is just quibbling. After all, just as all generated power shares the same grid, we all share the same airflow.

Meanwhile, we can look forward to further reductions in mercury as manufacturers continue to reduce the amount of mercury in their products, more attention is paid to lamp recycling, and the EPA’s Clean Air Mercury Rule goes into final implementation in 2018, which will reduce mercury emissions from coal-fired plants by nearly 70 percent.

To see the Yale report, visit pubs.acs.org. To view detailed EPA-recommended procedures for cleaning up a broken CFL, visit www.energystar.gov.

DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.