A compact fluorescent lamp (CFL), also known as a compact fluorescent light bulb or energy saving light bulb (or less commonly as a compact fluorescent tube [CFT]), is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit in the existing light fixtures formerly used for incandescents.
Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power and have a longer rated life, but generally have a higher purchase price. In the United States, a CFL can save over US $30 in electricity costs over the lamp's lifetime compared to an incandescent lamp and save 2000 times its own weight in greenhouse gases. Like all fluorescent lamps, CFLs contain mercury; this complicates the disposal of fluorescent lamps.
CFLs radiate a different light spectrum from that of incandescent lamps. Improved phosphor formulations have improved the subjective color of the light emitted by CFLs such that the best 'soft white' CFLs available in 2007 are subjectively similar in color to standard incandescent lamps.
The parent to the modern compact fluorescent lamp (CFL) was invented in the late 1890s by Peter Cooper Hewitt. The Cooper Hewitt lamps were used for photographic studios and industries. Edmund Germer, Friedrich Meyer, and Hans Spanner then patented a high pressure vapor lamp in 1927. George Inman later teamed with General Electric to create a practical fluorescent lamp, sold in 1938 and patented in 1941. The modern CFL was invented by Ed Hammer, an engineer with General Electric, in response to the 1973 oil crisis. While it met its design goals, it would have cost GE about US$25 million to build new factories to produce them and the invention was shelved. The design was eventually leaked out and copied by others.
There are two main parts in a CFL: the gas-filled tube (also called bulb or burner) and the magnetic or electronic ballast. An electrical current from the ballast flows through the gas, causing it to emit ultraviolet light. The ultraviolet light then excites a phosphor coating on the inside of the tube. This coating emits visible light (see Fluorescent lamp).
Electronic ballasts contain a small circuit board with rectifiers, a filter capacitor and usually two switching transistors connected as a high-frequency resonant series DC to AC inverter. The resulting high frequency, around 40 kHz or higher, is applied to the lamp tube. Since the resonant converter tends to stabilize lamp current (and light produced) over a range of input voltages, standard CFLs do not respond well in dimming applications and special lamps are required for dimming service. CFLs that flicker when they start have magnetic ballasts; CFLs with electronic ballasts are now much more common.
The ballasts make these light fixtures relatively expensive. They cost anywhere from $85 to $200 USD for each recessed can. If a ballast with dimming capabilities is desired the cost is anywhere from $125 to $300 USD per recessed can. Non-integrated CFLs are more popular for professional users, such as hotels and office buildings. The more advanced capabilities of these sophisticated external ballasts (e.g., faster starts, limited flicker, dimming, longer lifespans, etc.) are starting to appear in integrated CFLs.
Another style of non-integrated fitting is the "two piece", where the initial system includes a base adapter and detachable fluorescent tube module, and subsequently only the tube unit is replaced. The Thorn 2D and some Philips PL versions are examples, but while replacement tubes are generally still available, it is rare to see the complete kit on sale, having been overshadowed by cut-price one-piece units.
CFLs produce less light later in their life than they do at the start. The light output depreciation is exponential, with the fastest losses being soon after the lamp was first used. By the end of their lives, CFLs can be expected to produce 70-80% of their original light output. The response of the human eye to light is logarithmic: Each f-number (or photographic 'f-stop') reduction represents a halving in actual light, but is subjectively quite a small change. A 20-30% reduction over many thousands of hours represents a change of about half an f-stop, which is barely noticeable in everyday life.
For a given light output, CFLs use between one fifth and one third of the power of equivalent incandescent lamps. Since lighting accounted for approximately 9% of household electricity usage in the United States in 2001, widespread use of CFLs could save as much as 7% of total US household usage.
If indoor incandescent lamps are replaced by CFLs, the heat produced by the building's lighting system will be reduced. At times when the building requires both heating and lighting, the building's central heating system will then supply the heat. If the building requires both illumination and cooling, then CFLs will use less electricity themselves and will also reduce the load on the cooling system compared to incandescent lamps. This results in two concurrent savings in electrical power.
In order to compare the actual energy efficiency of CFLs with various other lamp technologies such as incandescent, LED and halogen, factors to compare include total luminous flux (in lumens), the usefulness of different frequencies of light, the distribution of light around the lamps, the efficiency of the CFL ballast and other factors.
CFLs are extremely cost-effective in commercial buildings. A CFL replacing a 75 W incandescent fixture offers an average yearly savings of $22 considering direct energy saving, reduced HVAC cost, and reduced labor to change lamps. The capital investment of $2 per fixture is typically paid back in about one month. Savings are greater and payback periods shorter in regions with higher than average electric rates and, to a lesser extent, also in regions with higher than average cooling requirements.
General Electric is attempting to develop more efficient incandescent bulbs that can produce the same light output as a 60-watt bulb (~800 lumens) but with half the wattage (30 watt). Their ultimate goal is to manufacture an incandescent bulb that will match the CFL's performance (a 15 watt bulb outputting 60-watt equivalency).
Some manufacturers make CFL bulbs with an external nano-particle coating of titanium dioxide. The manufacturer claims that the titanium dioxide when exposed to UV light produced by the CFL can neutralize odors and kill bacteria, viruses, and mold spores.
Some manufacturers add a coating of luminous paint to covered CFL bulbs so that they glow in the dark for a short time after they are turned off. The purpose is to provide lighting in an emergency, such as a blackout following a natural disaster. Some covered CFL bulbs incorporate this feature even though it is undocumented.
The Cold Cathode Fluorescent Lamp (CCFL) is one of the newest forms of CFL. CCFLs use electrodes without a filament. The voltage of CCFLs is about 5 times higher than CFLs and the current is about 10 times lower. CCFLs have a diameter of about 3 millimeters. CCFLs were initially used for backlighting LCD displays, but they are now also manufactured for use as lamps. The efficacy (lumens/watt) is about half that of CFLs. Their advantages are that they are instant-on, like incandescents, they are compatible with timers, photocells and dimmers, and they have a long life of approximately 50,000 hours. CCFLs are a convenient transition technology for those who are not comfortable with the short lag time associated with the initial lighting of CFLs. They are also an effective and efficient replacement for lighting that is turned on and off frequently with little extended use (e.g. a bathroom or closet).
Being a gas discharge lamp, a CFL will not generate all frequencies of visible light; the actual color rendering index (CRI) is a design compromise. Modern designs with high color rendering index are proving acceptable for home use. A mix of phosphors giving a good approximation of daylight or incandescent light can be used. 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 to achieve a 'white' light with a (CRI) of around 80, where 100 represents the appearance of colors under daylight or a blackbody (depending on the correlated color temperature).
|'Warm white' or 'Soft white'||≤ 3000 K||≥ 333 M|
|'White' or 'Bright White'||3500 K||-||'Cool white'||4000 K||250 M|
|'Daylight'||≥ 5000 K||≤ 200 M|
Color temperature is a quantitative measure. The higher the number in kelvins, the 'cooler', i.e., bluer, the shade. Color names associated with a particular color temperature are not standardized for modern CFLs and other triphosphor lamps like they were for the older-style halophosphate fluorescent lamps. Variations and inconsistencies exist among manufacturers. For example, Sylvania's Daylight CFLs have a color temperature of 3500 K, while most other lamps with a 'daylight' label have color temperatures of at least 5000 K. Some vendors do not include the kelvin value on the package, but this is beginning to change now that the Energy Star criteria for CFLs is expected to require such labeling in its 4.0 revision.
Some manufacturers now label their CFLs with a 3 digit code to specify the color rendering index (CRI) and color temperature of the lamp. The first digit represents the CRI measured in tens of percent, while the second two digits represent the color temperature measured in hundreds of kelvins. For example, a CFL with a CRI of 83% and a color temperature of 2700 K would be given a code of 827.
CFLs are also produced, less commonly, in other colors:
Black light CFLs, those with UVA generating phosphor, are much more efficient than incandescent black light lamps, since the amount of UV light that the filament of the incandescent lamp produces is only a fraction of the generated spectrum.
Other terms that apply to CFLs:
While CFLs require more energy in manufacturing than incandescent lamps, this is said to be offset by the fact that they last longer and use less energy than equivalent incandescent lamps during their lifespan.
CFLs, like all fluorescent lamps, contain small amounts of mercury as vapor inside the glass tubing,averaging 4.0 mg per bulb ,and it is a concern for landfills and waste incinerators where the mercury from lamps is released and contributes to air and water pollution. In the U.S., lighting manufacturer members of the National Electrical Manufacturers Association (NEMA) have voluntarily capped the amount of mercury used in CFLs. Some manufacturers such as Philips, GE, TCP Inc. and Turolight make very low mercury content CFLs. In 2007, Turolight claimed its new Genesis Fusion line contained only 1mg of mercury, making it the lowest EnergyStar approved bulb in North America.
In areas powered by coal, CFLs end up marginally saving on mercury emissions versus incandescent bulbs, due to the offset power use (coal releases mercury as it is burned). This effect is irrelevant in areas not powered by coal, and applies to bulbs which have run long enough to become dim as the mercury adheres to the glass. In old bulbs, as little as 11% of the mercury may be released.
Although initially dismissed as an overreaction, subsequent scientific studies by the Maine DEP and also Brown University in 2008 have confirmed that - contrary to earlier belief - the amount of mercury released by a broken CFL bulb greatly exceeds EPA safety standards.
Spent lamps should be recycled to contain the small amount of mercury in each lamp, in preference to disposal in landfills. Only 3 percent of CFL bulbs are properly disposed of or recycled. In the European Union, CFLs 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 CFLs. Safe disposal requires storing the bulbs unbroken until they can be processed. In the US, The Home Depot is the first retailer to make CFL recycling options widely available.
Special handling upon breakage is currently not printed on the packaging of household CFL bulbs in many countries. It is important to note that the amount of mercury released by one bulb can exceed U.S. federal guidelines for chronic exposure. Chronic however, implies that the exposure takes place over a long period of time. One time exposure to a trace amount of mercury is unlikely to be harmful. Conventional tubular fluorescent lamps have been used since 1938 with little concern about handling. The U.S. Environmental Protection Agency recommends that, in the absence of local guideline, fluorescent bulbs be double-bagged in plastic bags before disposal.
The first step of processing CFLs involves crushing the bulbs in a machine that uses negative pressure ventilation and a mercury-absorbing filter or cold trap to contain mercury vapor. Many municipalities are purchasing such machines. The crushed glass and metal is stored in drums, ready for shipping to recycling factories.
According to the Northwest Compact Fluorescent Lamp Recycling Project, because household users have the option of disposing of these products in the same way they dispose of other solid waste, "a large majority of household CFLs are going to municipal solid waste". They additionally note that an EPA report on mercury emissions from fluorescent tube lamp disposal indicates the percentage of total mercury released from the following disposal options: municipal waste landfill 3.2%, recycling 3%, municipal waste incineration 17.55% and hazardous waste disposal 0.2%.
Due to the potential to reduce electric consumption and pollution, various organizations have encouraged the adoption of CFLs and other efficient lighting. Efforts range from publicity to encourage awareness, to direct handouts of CFLs to the public. Some electric utilities and local governments have subsidized CFLs or provided them free to customers as a means of reducing electric demand (and so delaying additional investments in generation).
More controversially, some governments are considering stronger measures to entirely displace incandescents. These measures include taxation, or bans on production of incandescent light bulbs. Australia and Canada have already announced nationwide bans on incandescent bulbs.