How does a compact fluorescent light­bulb save energy?
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How does a fluorescent lamp (fluorescent tube) work? How does a compact fluorescent light­bulb (CFL) work? How much energy does a CFL save? How long does a CFL typically last? Do CFLs have any health issues? Since fluorescent lamps and CFLs emit ultraviolet light, why don't I get sunburn? What is the world trend in the choice of light bulbs? Written by: LEE Boon­ying 1. How does a fluorescent lamp (fluorescent tube) work? In a modern fluorescent lamp, a ballast is used to produce a high voltage that causes an electric
discharge across the electrodes. The discharge excites the mercury vapour inside the lamp,
giving out ultraviolet light. The ultraviolet light hits on the phosphor coatings on the glass, which
produces visible light. The ballast then maintains the current, working at a lower voltage to
sustain the discharge after the gas inside the lamp has been ionized. Fluorescent lamps in the older days, using starters and "magnetic ballasts", flickered when
started and might take seconds or even minutes to stabilize. Such inconvenience has gone
with the advent of "electronic ballasts", which have also made possible lamps of smaller size. Back to content
2. How does a compact fluorescent light­bulb (CFL) work? CFL works in the same way as a fluorescent lamp, except that the glass tube is bent. Both
ends of the tube are affixed onto a base which also holds a ballast and can fit an ordinary light­
bulb socket. Photo: Courtesy of H.Y. Chiu
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3. How much energy does a CFL save? An ordinary light bulb uses only 10 to 12% of the input energy to generate light (the rest is
mostly emitted as heat). A halogen lamp is about the same. Please refer to "How to make light
bulbs last longer". In comparison, a CFL is about 4 times as efficient, i.e. it uses about 40 to
50% of the energy. Thus, a 25­watt CFL is as bright as a 100­watt light bulb. Back to content
4. How long does a CFL typically last? A CFL typically can last for about 8,000 hours. In comparison, an ordinary light bulb lasts about
900 hours only. Taking account of its energy efficiency and longer life, a CFL outperforms an ordinary light bulb
by more than 30 times. Back to content
5. Do CFLs have any health issues? CFLs have the same health issues as fluorescent lamps:­ a. They need to be disposed of carefully to avoid mercury contamination.
b. Some consumers find the light too harsh. This is because the phosphor coatings on the
glass do not emit all the lights in the visible­light spectrum. The human eye, on the other
hand, would like to see all of them. c. Some people are sensitive to ultraviolet light.
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6. Since fluorescent lamps and CFLs emit ultraviolet light, why don't I get sunburn? Research indicates that 8 hours of exposure under office fluorescent lighting is about the same
as 1 minute under the sun. So, no sunburn. Back to content
7. What is the world trend in the choice of light bulbs? Under a new law in the United States, by the early 2010s manufacturers of ordinary light bulbs
are required to make them generally 30% more efficient. Europe has also made its own
rules. Since CFLs are already better by more than 30 times in terms of energy efficiency and
expected lifetime combined, it is expected that more consumers will turn to CFLs. Back to content
Reference: 1. "The switch is on", Scientific American, p.84, March 2008. 2. "What Einstein told his barbar", R.L. Wolke, Dell Publishing, 2000.