Compact Fluorescent Light Bulbs (CFLs) contain a very small amount of mercury sealed within the glass tubing an average of 4 milligrams (mg). By comparison, older thermometers contain about 500 mgs of mercury an amount equal to the mercury in 125 CFLs. Mercury is an essential part of CFLs; it allows the bulb to be an efficient light source. No mercury is released when the bulbs are intact (not broken) or in use. Most makers of light bulbs have reduced mercury in their fluorescent lighting products. Thanks to technology advances and a commitment from members of the National Electrical Manufacturers Association, the average mercury content in CFLs has dropped at least 20% or more in the past several years. Some manufacturers have even made further reductions, dropping mercury content to 1 mg per light bulb. Because CFLs contain mercury, they should be disposed of properly. Follow proper clean-up recommendations if a CFL breaks in your home: epa.gov/cflcleanup.