Compact Fluorescent Light Bulbs

Technology basics

Compact fluorescent bulbs consist of an electronic ballast and a glass tube containing mercury vapor and other gases. The ballast controls a current that flows through the gas, exciting the atoms’ electrons causing them to emit ultraviolet light. This UV light is converted to visible wavelengths by phosphors that coat the interior of the glass tube. Different combinations of phosphors emit different combinations of light wave lengths.

Energy and cost efficiency

CFLs use approximately 75% less energy than incandescent light bulbs.³ Incandescent bulbs used for household lighting typically require 60-100 watts compared to the 13-25 watts required by CFLS. ⁴ Incandescent bulbs use a  heat-based lighting mechanism.

An electric current heats a tungsten filament until it glows.  As a result, a large amount – approximately 90% – of energy used by an incandescent bulb is wasted as heat ⁵. Since lighting accounts for 20% of an average house’s electricity bill ⁶, homeowners can save large amounts of money on utilities by exchanging their incandescent bulbs for CFLs, depending on local electricity costs.

In addition to reducing electricity use devoted to lighting, outfitting fixtures with CFLs can help to decrease home cooling costs. The large amount of heat that incandescent bulbs generate can raise indoor temperatures, requiring extra energy-intensive air conditioning in hot weather. ⁷

CFLs have longer lifespans than incandescent bulbs, an attribute that may help decrease the amount of energy that light bulb manufacturing requires. On average, a CFL lasts ten times longer than a similar incandescent bulb ⁸.

Mercury content

Mercury is essential in the production of CFLs, which contain an average of four milligrams per bulb. ⁹ Some manufacturers now make CFL's with less than two milligrams of mercury ,¹⁰ but the disposal of CFLs and treatment of broken CFLs still require extra care.

Some accounting methods show the amount of mercury contained in a CFL to be less than what would be released by a coal fired power plant providing electricity to an incandescent bulb. Electricity generation is the main source of mercury emissions in the US; therefore, widespread adoption of CFLs could help to decrease mercury pollution overall. ¹¹ As CFLs are used, most of the mercury contained within them binds to the interior coating of the tubes, resulting in decreased danger to a home’s residents and to the environment, should the bulb break. ¹²

Because of their mercury content, broken or nonfunctional CFLs should be treated as household toxic waste. Homeowners should contact their local toxic waste facility and/or CFL recycling program for instructions on proper disposal. Cleaning up a broken CFL requires good ventilation and minimized contact with the bulb’s broken pieces.

Footnotes

¹: "Energy Efficient Lighting", eartheasy.com, retrieved Feb. 12, 2009

²: “Coal vs. Wind," Union of Concerned Scientists, retrieved Jan 8 2009.

^{3 6 7 8 9}: “Compact Fluorescent Light bulbs," EnergyStar, retrieved Jan 8 2009.

⁴: Michael Kanellos (August 2007), “Father of the compact fluorescent bulb looks back," CNet News, retrieved Jan 8 2009.

⁵: “US Household Electricity Report”. US Energy Information Administration (2005).

¹⁰: “Low Mercury CFLs”, Energy Federation Incorporated, retrieved Jan 8, 2009.

¹¹¹²: “Frequently Asked Questions: Information on Compact Fluorescent Light Bulbs (CFLs) and Mercury”, EPA, 2008.

Resources

• Compact Fluorescent Light Bulbs, Products, Energy Star, U.S. EPA/U.S. DOE. Accessed 11 Feb 08.
• "Information on Compact Fluorescent Light Bulbs (CFLs) and Mercury," (pdf) Energy Star, U.S. EPA/U.S. DOE, July 2008. Accessed 11 Feb 08.
• "Compact Fluorescent Lights Are Safe for Your Home," (pdf) Health Facts, NRDC, May 2008. Accessed 11 Feb 08.