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A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb or an energy saving lightbulb, is a type of fluorescent lamp that screws into a regular light bulb socket or plugs into a small lighting fixture.
In comparison to incandescent light bulbs, CFLs have a longer rated life and use less electricity. In fact, CFLs save enough money in electricity costs to make up for their higher inital price within about 500 hours of use.
Market
Globally introduced in the early 1980s, CFLs have steadily increased in sales volume, largely due to improvements in product performance and reduction in unit prices. The most important advance in fluorescent lamp technology (including in CFLs) has been the gradual replacement of magnetic ballasts with electronic ballasts: This has removed most of the flickering and slow starting traditionally associated with fluorescent lighting.
The market for CFLs has been aided by the production of both integrated and non-integrated lamps. Integrated lamps combine a bulb, an electronic ballast and either a screw or bayonet fitting; these lamps allow consumers to easily replace incandescent bulbs with CFLs. Non-integrated lamps allow for the replacement of consumable bulbs and the extended use of ballasts; since the ballasts last longer, they can be more expensive and sophisticated, providing options such as dimming. (Non-integrated CFLs are more popular for professional users, such as hotels.)
CFLs are produced for both AC input and DC input. DC CFLs are popular for use in recreational vehicles and off-the-grid housing. Poor families in developing countries are using DC CFLs (with car batteries and small solar panels) to replace kerosene lanterns.
Comparing CFLs and incandescent bulbs
| Equivalent light output | |
|---|---|
| Incandescent | Compact fluorescent |
| 40 W | 8–9 W |
| 60 W | 11–15 W |
| 75 W | 18–20 W |
| 100 W | 22–25 W |
CFLs are typically guaranteed for 8,000 hours. (Incandescent bulbs typically last 500 to 2000 hours, depending on exposure to voltage spikes and mechanical shock.)
CFLs use about a quarter the amount of energy. For example, a 15-watt CFL produces the same amount of light as a 60-watt incandescent bulb (approximately 900 lumens). Let us compare the purchase and operating costs of these two light sources.
The kilowatt-hour (kWh) is the unit used to sell electrical energy in most countries. The cost of electricity in the United States ranges from $0.06 to $0.38 per kWh, with an average cost of $0.09 per kWh (see Electricity rates.)
For convenience, a rate of $0.10 per kWh is often used for estimating the running costs of appliances.
The CFL, therefore, will save $36.00 in electricity (compared to the incandescent bulb) during its rated life. American discount stores sell packages of CFLs for $2.75 each and incandescent bulbs for $0.50 each; a $2.25 difference. The estimated payback period for buying the CFL instead of the incandescent bulb is, therefore, 500 hours, which is 100 days at 5 hours per evening.
The above calculations do not account for the ancillary effect of (light bulb) heat on energy costs. The energy that is not used to create light is instead converted into heat energy. Incandescent bulbs therefore produce substantially more heat than CFLs for a given light output. By comparison: During cold months, incandescent bulbs can help to heat buildings; and during hot months, incandescent bulbs place additional strain on air conditioning systems.
Colors
CFLs are produced in varying shades of white:
- "Warm white" (2,700 K) provides a light extremely similar to that of an incandescent bulb, somewhat yellow in appearance;
- "Soft white" (3,500 K) bulbs produce a yellowish-white light;
- "Cool white" (4,100 K) bulbs emit more of a pure white tone; and
- "Daylight" (6,400 K) is slightly bluish-white.
CFLs are also produced, less commonly, in other colors:
- Red, green, and pink, primarily for novelty purposes;
- Yellow, for outdoor lighting, does not attract insects; and
- Blacklight, for special effects.
Being a gas discharge lamp, a CFL will not generate all frequencies of visible light; the actual color rendering index is a design compromise (see below). With less than perfect color rendering, CFLs can be unsatisfactory for inside lighting, but modern, high quality designs are proving acceptable for home use.
Environmental concerns
CFLs contain trace amounts of mercury. The amount is not large enough to pose a hazard to users, but it does become a concern at landfills and trash incinerators where the mercury from many bulbs can escape and contribute to air and water pollution.
Safe disposal requires storing the bulbs unbroken until they can be processed. Consumers should seek advice from local authorities. Usually, one can either:
- Bring back used CFLs to where they were purchased, so the store can recycle them correctly; or
- Bring used CFLs to a local recycling facility.
The first step of processing involves crushing the bulbs in a machine that uses negative pressure ventilation and a mercury-absorbing filter or cold trap to contain and treat the contaminated gases. Many municipalities are purchasing such machines. The crushed glass and metal is stored in drums, ready for shipping to recycling factories.
Note that coal power plants are the single largest source of mercury emissions into the environment. According to the Environmental Protection Agency (EPA), (when coal power is used) the mercury released from powering an incandescent bulb for five years exceeds the sum of the mercury released by powering a comparably luminous CFL for the same period and the mercury contained in the lamp. *
How they work
Parts
There are two main parts to a CFL: the gas-filled tube (also called bulb or burner) and the magnetic or electronic ballast. Electrical energy in the form of an electrical current from the ballast flows through the gas, causing it to give off ultraviolet light. The ultraviolet light then excites a white phosphor coating on the inside of the tube. This coating emits visible light. CFLs that flicker when they start have magnetic ballasts; CFLs with electronic ballasts are now much more common. See Fluorescent lamp.
End of life
Both the ballast and the burner are subject to failure from normal use. In low-quality CFLs, high temperatures often cause the ballast electronics to fail before the burners. In high-quality CFLs, the burners almost always fail first. The burners occasonally fail due to cracks and imperfect seals but much more typically due to an increased work function at the electrodes caused by vaporization and sputtering-off of the cathode material. It is also this material that then deposits onto the burner's glass tubing, causing blackening of the tubing.High-quality driver electronics can prolong the life of the burners by preheating the electrodes to prevent damage from rapid expansion. High-quality drivers require high-quality components. The best CFL manufacturers (including Osram, Philips, General Electric and Luxlite) produce CFLs that can last 15,000 hours. Such lifetimes require highly automated and controlled manufacturing.
At end of life, CFLs should be recycled by specialist firms. In the European Union, CFL lamps are one of many products subject to the WEEE recycling scheme. The retail price includes an amount to pay for recycling, and manufacturers and importers have an obligation to collect and recycle CFL lamps.
Design compromises and challenges
Apart from durability, the primary purpose of good CFL design is high electrical efficiency.These are some other areas of interest:
- Quality of light: A phosphor emits light in a narrow frequency range, unlike an incandescent filament, which emits the full spectrum, though not all colors equally, of visible light. Mono-phosphor lamps emit poor quality light; colors look bad and inaccurate. The solution is to mix different phosphors, each emitting a different range of light. Properly mixed, a good approximation of daylight or incandescent light can be reached. However, every extra phosphor added to the coating mix causes a loss of efficiency and increased cost. Good-quality consumer CFLs use three or four phosphors - typically emitting light in the red, green and blue spectra - to achieve a "white" light with color rendering indexes (CRI) of around 80. (A CRI of 100 represents the most accurate reproduction of all colors; reference sources having a CRI of 100, such as the sun and tungsten bulbs, emit black body radiation.)
- Covered performance: To approximate the look of an incandescent bulb, the CFL burner can be enclosed behind a cosmetic glass cover. However, this causes the temperature of the burner to increase greatly, increasing the gas pressure inside the burner and decreasing the brightness (and therefore efficiency) of the lamp. These problems have largely been solved using special mercury compounds and other techniques, and now globe and flood versions are widely available (at hardware stores and elsewhere).
- Electronics: Dimming control can be added to the lamp with support from the driver electronics. Also, large deployments of CFLs (in a hotel lobby, for example) require specialised electronics with low levels of electronic distortion to avoid disturbing the electricity supply. This is usually not a problem with home use because of the few lamps deployed.
- Time to achieve full brightness: Compact fluorescent bulbs can take 30 seconds or more to reach full brightness. This compares to 0.1 seconds for incandescent bulbs and 0.01 seconds for LED lamps.
- CFLs do not fail according to good/dead binary logic applicable to incandescent lighbulbs. Symptoms of impending CFL failure may come months ahead, with more and more prolonged turn-on times until full lumionsity is reached, buzzing of the ballast, random periods of reduced brightness and the appearance of growing black spots on the glass tubing's inside.
- In places infested with insects, bugs have a habit of climbing into the "cage" formed by the CFL tubing and perish inside. Some CFL have extra an oval shell hiding the tubeworks for this purpose.
Other CFL technologies
Another type of CFL is the electrodeless lamp (sometimes called a radiofluorescent lamp or RFL), which uses radio waves instead of an electric current to ionize the mercury to produce the ultraviolet light used to excite the phosphors.
Another variant of the CFL is coated (outside the bulb) with titanium dioxide, which the manufacturer claims reduces odors by ionization and oxidation.
The Cold Cathode Fluorescent Light (CCFL) is one of the newest forms of CFL. CCFLs typically produce less heat because of their small size, but it is often claimed by marketers that CCFL CFL's are more energy efficient. This is not true. But at least they are typically more compact, and last longer than conventional CFLs.
Efforts to encourage adoption
The public has been slow to transition from incandescent blubs to CFLs. Consumers expect a much faster rate of return on investments that reduce costs than on investments that pay earnings. For example, most people would consider a rental property that paid for itself (and its interest costs) in 10 years to be a good investment. However, people are reluctant to buy CFLs despite their 3- to 12-month payback period. Also, lighting is often installed by disinterested parties (e.g., contractors who do not pay for the electricity for that lighting).
Consequently, governments have attempted to encourage CFL use by handing them out free and by appealing to people's morals. Controversially, some in Britain have lobbied Parliament to tax or ban incandescent bulbs. Activist Dr Matt Prescott created banthebulb.org, as reported by the BBC. (For the BBC article, see here. For a viewpoint that opposes governments intervening to secure appliance efficiency, see here.)
In June 2006, Environmental Defense initiated a campaign called Make the Switch to encourage the public to switch from incandescent bulbs to compact fluorescent bulbs. They asked every household in the US to replace three 60-watt incandescent bulbs with CFLs: a 15-watt CFL is just as bright as a 60-watt incandescent. If every household were to make this simple switch, it could reduce as much pollution as taking 3.5 million cars off the road and contribute to the fight against global warming. CFLs cost more to purchase than incandescent bulbs, but they last much longer and save money in the long run.
Gallery of CFLs
References
- R. J. Van der Plas, A. B. de Graaff, "A comparison of lamps for domestic lighting in developing countries" (Energy Ser. Pap. 6, Industry and Energy Department, World Bank, Washington, DC, 1988).
- G. S. Dutt, "Illumination and Sustainable Development", Energy Sustain Dev. 1 (1), 23 (1994).
External links
- Compact Fluorescent Lamps: What You Should Know
- Energy Star's page on fluorescent bulbs
- Energy saving calculator
- Energy Savings
- How Fluorescent Lamps Work
- Make the Switch Campaign, Environmental Defense
- Reduce Global Warming
- How much coal is required to run a 100-watt light bulb 24 hours a day for a year? - from HowStuffWorks.com
- LampRecycle.Org - For information on recycling spent mercury-containing lamps
- Mercury in Compact Fluorescent Lamps - from the National Electrical Manufacturers Association
- Compact Fluorescent Pitfalls, Reality, and Recommendations
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