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Compact fluorescent lamp

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.


Globally introduced in the early 1980s, CFLs have steadily increased in sales volume. The most important technical advance has been the gradual replacement of electromagnetic ballasts with electronic ballasts; this has removed most of the flickering and slow starting traditionally associated with fluorescent lighting. There are two types of CFLs: integrated and non-integrated lamps.


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.

Integrated CFLs

Integrated lamps combine a tube, an electronic ballast and either an Edison screw or bayonet fitting in a single CFL unit. These lamps allow consumers to replace incandescent lamps easily with CFLs. Integrated CFLs work well in standard incandescent light fixtures. This lowers the cost of CFL use, since they can reuse the existing infrastructure. In addition, incandescent light fixtures are relatively inexpensive. Special 3-way models and dimmable models with standard bases are available for use when those features are needed.

Non-integrated CFLs

Non-integrated CFLs have a separate, replaceable bulb and a permanently installed ballast. Since the ballasts are placed in the light fixture they are larger and last longer, compared to the integrated ones. Non-integrated CFL housings can be both more expensive and sophisticated, providing options such as dimming, less flicker, faster starts, etc.

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.

CFL power sources

CFLs are produced for both alternating current (AC) and direct current (DC) input. DC CFLs are popular for use in recreational vehicles and off-the-grid housing. Some families in developing countries are using DC CFLs (with car batteries and small solar panels) and/or wind generators, to replace kerosene lanterns.

CFLs can also be operated with solar powered street lights, using solar panels located on the top or sides of a pole and luminaires that are specially wired to use the lamps.

Comparison with incandescent lamps


The average rated life of a CFL is between 8 and 15 times that of incandescents. CFLs typically have a rated lifespan of between 6,000 and 15,000 hours, whereas incandescent lamps are usually manufactured to have a lifespan of 750 hours or 1,000 hours. Some incandescent bulbs with long rated lifespans of 20,000 hours have reduced light output. The lifetime of any lamp depends on many factors including operating voltage, manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off, lamp orientation and ambient operating temperature, among other factors. The life of a CFL is significantly shorter if it is only turned on for a few minutes at a time: In the case of a 5-minute on/off cycle the lifespan of a CFL can be up to 85% shorter, reducing its lifespan to the level of an incandescent lamp. The US Energy Star program says to leave them on at least 15 minutes at a time to mitigate this problem.

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.

Energy efficiency

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.


While the purchase price of an integrated CFL is typically 3 to 10 times greater than that of an equivalent incandescent lamp, the extended lifetime and lower energy use will compensate for the higher initial cost. A US article stated "A household that invested $90 in changing 30 fixtures to CFLs would save $440 to $1,500 over the five-year life of the bulbs, depending on your cost of electricity. Look at your utility bill and imagine a 12% discount to estimate the savings.

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.

Starting time

Incandescents give light almost immediately upon the application of voltage. CFLs take a perceptible time to achieve full brightness, and can take much longer in very cold temperatures. Certain styles of lamp using a mercury amalgam can take up to three minutes to reach full output. Coupling this with the shorter life of CFLs when turned on and off for short amounts of time may make incandescent bulbs more attractive for applications such as outdoor or motion-activated lighting.

Comparison with alternative technologies

Solid-state lighting has already filled a few specialist niches such as traffic lights and may compete with CFLs in the near future. LED lamps have current efficiencies of 30% with higher levels attainable (recently up to 85 lm/W LEDs are available), and a lifetime of around 50,000 hours. Currently LED lamps do not deliver the intensity of light output for domestic uses at a reasonable cost.

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).

Other CFL technologies

Another type of fluorescent lamp is the Electrodeless lamp, known as a radiofluorescent lamp or fluorescent induction lamp. These lamps have no wire conductors penetrating their envelopes, and instead excite mercury vapor using a radio-frequency oscillator. Currently, this type of light source is struggling with a high cost of production, stability of the products produced in China, establishing an internationally recognized standard and problems with EMC and RFI. Induction lighting is excluded from Energy Star standard for 2007 by the EPA.

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).

Spectrum of light

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).

Color temperature can be indicated in kelvins or mireds (1 million divided by the color temperature in kelvins).

Color temperature kelvin mired
'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:

Environmental issues

Energy savings

Since compact fluorescent uses less power to supply the same amount of light as an incandescent lamp, they decrease energy consumption and the environmental effects of electric power generation. Where electricity is largely produced from burning fossil fuels, the savings reduces emissions of greenhouse gases and other pollutants; in other areas the reduction may help reduce negative impacts from radioactive waste, hydroelectric plants, or other sources.

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.

Mercury emissions

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.

Broken and discarded lamps

Public adoption of CFLs has been slowed by one widely-circulated story of how the Maine Department of Environmental Resources detected mercury contamination following a residential CFL breakage incident, and the homeowner was presented with a US$2,000 estimate from an environmental cleanup firm.

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%.

Design and application issues

The primary purposes of CFL design are high electrical efficiency and durability. However, there are some other areas of CFL design and operation that are problematic:

  • Size: CFL light output is roughly proportional to phosphor surface area, and high output CFLs are often larger than their incandescent equivalents. This means that the CFL may not fit well in existing light fixtures.
  • End of life: A detailed description of the failure modes of fluorescent lamps is given in the Fluorescent lamp article. Additionally, the electronic ballast may fail since it has a number of component parts; such failures may be accompanied by discoloration or distortion of the ballast enclosure, odors, or smoke. The lamps are internally protected and are meant to fail safely at the end of their lives. Industry associations are working toward advising consumers of the different failure mode of CFLs compared to incandescent lamps, and to develop lamps with inoffensive failure modes.
  • Dimming: Only a few CL lamps are labeled for dimming control. Using regular CFLs with a dimmer can shorten bulb life and will void the warranty of certain manufacturers. According to BC Hydro and Environmental Defense, dimmable screw-in fluorescent lamps are now available. The dimming range of CFLs is usually between 20% and 90%. Dimmable CFLs are not a 100% replacement for incandescent fixtures that are dimmed for "mood scenes" such as wall sconces in a dining area. Below the 20% limit, the lamp remain at the approximate 20% level, in other cases it may flicker or the starter circuitry may stop and restart. Above the 80% dim limit, the bulb will generally glow at 100% brightness. Dimmable CFLs have a higher purchase cost than standard CFLs due to the additional circuitry required for dimming. A further limitation is that multiple dimmable CFLs on the same dimmer switch may not appear to be at the same brightness level.
  • Perceived Coldness of Low Intensity CFL: When a CFL is dimmed the colour temperature (warmth) stays the same. This is counter to most other light sources (such as the sun or incandescents) where colour gets warmer as the light source gets dimmer. Emotional Response Testing suggests that people find dim, bluish light sources to be cold or even sinister. This may explain the persistent lack of popularity for CFL's in bedrooms and other settings where a subdued light source is preferred.
  • Heat: Some CFLs are labeled not to be run base up, since heat will shorten the ballast's life. Such CFLs are unsuitable for use in pendant lamps and especially unsuitable for Recessed light fixtures. CFLs for use in such fixtures are available. Current recommendations for fully enclosed, unventilated light fixtures (such as those recessed into insulated ceilings), are either to use 'reflector CFLs' (R-CFL) or to replace such fixtures with those designed for CFLs.
  • Large deployments of CFLs require specialized electronics with low levels of electronic distortion to avoid disturbing the electricity supply. Unless corrected, electronic ballasts have a low power factor due to their rectifier input stage. This is usually not a problem with home use because of the few lamps deployed per home and because current drain is less than that of the replaced incandescent lamps.
  • Time to achieve full brightness: Compact fluorescent lamps may provide as little as 50-80% of their rated light output at initial switch on and can take up to three minutes to warm up, and color cast may be slightly different immediately after being turned on. This compares to around 0.1 seconds for incandescent lamps. In practice, this varies between brands/types. It is more of a problem with older lamps, 'warm (color) tone' lamps and at low ambient temperatures.
  • Infrared signals: Electronic devices operated by infrared remote control can interpret the infrared light emitted by CFLs as a signal limiting the use of CFLs near televisions, radios, remote controls, or mobile phones.
  • Audible noise: CFLs, much as other fluorescent lights, may emit a buzzing sound, where incandescents normally do not. Such sounds are particularly noticeable in quiet rooms, and can be annoying under these circumstances. Newer compact fluorescent light bulbs are nearly noiseless, but some poorly made CFLs may still emit a buzzing sound.
  • Use with timers: Electronic (but not mechanical) timers can interfere with the electronic ballast in CFLs and can shorten their lifespan.
  • Fire hazard: Inferior quality electronic components used in some CFLs can cause excessive heat or fire.
  • Outdoor use: CFLs not designed for outdoor use will not start in cold weather. CFLs are available with cold-weather ballasts, which may be rated to as low as -23°C (-10°F). Standard compact fluorescents will fail to operate at low temperatures. Light output drops at low temperatures.
  • Differences among manufacturers: There are large differences among quality of light, cost, and turn-on time among different manufacturers, even for lamps that appear identical and have the same color temperature.
  • Fluorescent lamps get dimmer over their lifetime, so what starts out as an adequate luminosity may become inadequate. In one test by the US Department of Energy of 'Energy Star' products in 2003-4, one quarter of tested CFLs no longer met their rated output after 40% of their rated service life.

Efforts to encourage adoption

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.

Energy Star program

In the United States and Canada, the Energy Star program labels compact fluorescent lamps that meet a set of standards for starting time, life expectancy, color, and consistency of performance. The intent of the program is to reduce consumer concerns due to variable quality of products. Those CFLs with a recent Energy Star certification start in less than one second and do not flicker. There is ongoing work in improving the 'quality' (Color Rendering Index) of their light.

Notes and references

External links

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