Compact Fluorescent Light Bulbs

Introduction

A compact fluorescent light bulb is a device that creates light using about one fourth as much power as a conventional, incandescent light bulb for a given amount of light. Large amounts of electricity are used to power light bulbs in industrial countries. Because most electricity worldwide is generated by burning coal, which releases the greenhouse gas carbon dioxide (CO₂), replacing incandescent bulbs with compact fluorescent light bulbs (CFLs) can reduce the amount of greenhouse gases emitted, especially in warmer climates, and have an impact on the amount of global climate change. CFLs contain small amounts of the toxic metal mercury and are more expensive than incandescent light bulbs. They last longer than incandescents and, averaged over the lifetime of the device, cost less to run.

Historical Background and Scientific Foundations

Conventional light bulbs operate on the principle of heating a small wire or filament until it glows brightly. Most of the energy consumed by an incandescent bulb is turned into heat, not light. Fluorescent light bulbs operate on the principle that certain gas mixtures, such as mercury vapor mixed with xenon or argon, emit ultra-violet radiation (a form of light invisible to the human eye) when excited by an electric current. A coating on the inside of a glass tube filled with such a gas can absorb the ultraviolet radiation and re-radiate it as visible light.

Incandescent bulbs convert about 90% of the electricity they consume into heat, whereas fluorescent light bulbs convert only about 30% into heat. The result is that a fluorescent bulb uses much less electricity to provide a given amount of light. Heat from light bulbs is often undesirable. In air-conditioned buildings, for example, electricity must be purchased to remove the heat produced by interior lighting, so owners pay twice, once to make the unwanted heat and once to remove it.

Scientists first noticed the production of electromagnetic radiation by electrified gases in the late nineteenth century. The invention of the commercial fluorescent light bulb is credited to German inventor Edmund Germer (1901–1987), who in 1926 patented a fluorescent bulb that used an inner bulb coating to convert ultraviolet light to relatively pleasing white light.

Fluorescent lights have traditionally been designed as long tubes, either straight or looping, because lower electric currents (which are easier to produce and safer for the consumer) are needed to produce a given amount of light from a longer tube. Small or “compact” fluorescent light bulbs that could be screwed into a conventional light socket would require either complex, maze-like glassware to pack long gas paths into small volumes or high currents that would waste power.

In the 1970s, a number of inventors sought solutions to these design barriers. Several designs that worked in the laboratory were produced, but no commercially viable design was put forward until the idea of bending a tube into a double-spiral shape was invented by Edward Hammer at the General Electric Corporation in 1976. Although it was more difficult and expensive to make such tubes than to make conventional bulbs, gradual improvements in technique made it possible for spiral-bulb compact fluorescents to be marketed starting in 1995.

Impacts and Issues

CFLs cost much more per unit than incandescent light bulbs, but last longer: about 7,500 hours versus only 1,000 for an incandescent bulb. Because they use less power, burden air conditioning less, and last longer, they end up costing less despite their higher up-front cost. A savings of $30 or more per bulb is cited by the U.S. Environmental Protection Agency (EPA) when CFLs are used instead of traditional incandescent bulbs. Because most electricity is generated by burning coal and CFLs save electricity, CFLs tend to cause less carbon dioxide to be emitted, which helps mitigate global climate change.

Globally, electric lighting causes carbon dioxide emissions equivalent to 70% of those from passenger vehicles. Thus, if every American home replaced just one incandescent bulb with a CFL, the carbon dioxide savings would be roughly equivalent to taking 800,000 cars off the road. Because of the cost and other advantages, some governments have considered, or have taken, action to speed the replacement of incandescent with fluorescent bulbs. In 2007, Australia became the first nation to announce that it would phase out incandescent bulbs entirely by 2012. Also in 2007, California was considering legislation that would ban the sale of incandescent light bulbs between 25 watts and 150 watts.

WORDS TO KNOW

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

ULTRAVIOLET: Light that vibrates or oscillates at a frequency of between 7.5 x 10¹⁴ and 3 x 10¹⁶ Hz (oscillations per second), more rapid than the highest-frequency color visible to the human eye, which is violet (hence the term “ultraviolet,” literally above-violet). Ultraviolet light is absorbed by ozone (O₃) in Earth's stratosphere. This absorption serves both to shield the surface from this biologically harmful form of radiation and to heat the stratosphere, with important consequences for the global climate system.

WATT: Unit of power or rate of expenditure of energy. One watt equals 1 joule of energy per second. A 100-watt light bulb dissipates 100 joules of energy every second, i.e., uses 100 watts of power. Earth receives power from the sun at a rate of approximately 1.75 x 10¹⁷ watts.

American consumers have been slow to adopt CFLs: only 2% to 5% of the 2 billion light bulbs sold in the United States each year are CFLs. Critics have pointed out that CFLs, like all fluorescent bulbs, contain the highly toxic metal mercury—about 5 milligrams (mg) per bulb. About 600 million fluorescent bulbs containing a total of 13,600 kg (30,000 lb) of mercury are thrown into U.S. landfills every year. However, because coal-burning also releases mercury and because CFLs prevent the burning of so much coal, an incandescent bulb causes the release, on average, of about 3.7 times more mercury per hour of lighting provided than does a CFL.

A more efficient, less toxic, and longer-lasting lighting technology—light-emitting diodes (LEDs)—is currently under development. LEDs remain relatively expensive, however, and are unlikely to displace CFLs in most applications in the near future.

Because of their mercury content, broken CFLs should not be touched with bare hands. They should also be recycled as toxic waste, not dumped in ordinary trash. Such dumping is illegal in California and several other U.S. states.

See Also Energy Efficiency; Solar Illumination.

BIBLIOGRAPHY

Periodicals

Kleiner, Kurt. “Shades of Success.” Nature 447, no. 7146 (June 14, 2007): 766–767.

Yi, Matthewe. “Lawmaker Takes on Light Bulbs.” San Francisco Chronicle (February 9, 2007): B1.

Web Sites

“Compact Fluorescent Bulbs and Mercury: Reality Check.” Popular Mechanics, June 11, 2007. < http://www.popularmechanics.com/blogs/home_journal_news/4217864.html> (accessed August 6, 2007).

“Compact Fluorescent Light Bulbs.” U.S. Environmental Protection Agency (EPA). < http://www.energystar.gov/index.cfm?c=cfls.pr_cfls> (accessed August 6, 2007).

Larry Gilman