Why do CFLs contain mercury?
Mercury is essential in compact fluorescent lamps (CFLs). It allows the bulbs to be efficient light sources. Mercury is safely contained inside CFLs when the bulbs are in use and as long as the bulbs are not br`oken.

How much mercury is in CFLs?
According to the U.S. Environmental Protection Agency (EPA), CFLs contain an average of four milligrams of mercury sealed within the glass tubing. That’s a very small amount, about enough to cover the tip of a ballpoint pen. By comparison, older fever thermometers contain about 500 milligrams of mercury – an amount equal to the mercury in 125 CFLs.

Are manufacturers doing anything about mercury in CFLs?
Yes, most light bulb manufacturers have voluntarily reduced mercury in their fluorescent lighting products. Thanks to better technology and a commitment from the National Electrical Manufacturers Association, the average mercury content in CFLs has dropped at least 20 percent in recent years.

Overall, which is environmentally better – CFLs or incandescent light bulbs?
The U.S. EPA has this to say: “Because CFLs also help to reduce greenhouse gasses, other pollutants associated with electricity production, and landfill waste (because the bulbs last longer), they are clearly the environmental winner when compared to traditional incandescent light bulbs.”

For more information

How to Safely Dispose of CFLs

EPA Mercury-Containing Light Bulb Frequent Questions:

EPA Fact Sheet:  How to Dispose of Compact Fluorescent Lamps: CFLs and Mercury (PDF, 72KB)