Compact fluorescent lamp

Compact fluorescent lamp
The tubular-type compact fluorescent lamp is one of the most popular types in Europe.
A helical integrated CFL. It has been the most popular type in North America since the mid 1990s, when the final expiration of patents allowed its manufacture.[1]

A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent lamp; some types fit into light fixtures formerly used for incandescent lamps. The lamps use a tube which is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp.

Compared to general-service incandescent lamps giving the same amount of visible light, CFLs use less power (typically one fifth) and have a longer rated life (six to ten times average). In most countries, a CFL has a higher purchase price than an incandescent lamp, but can save over five times its purchase price in electricity costs over the lamp's lifetime.[2] Like all fluorescent lamps, CFLs contain mercury, which complicates their disposal. In many countries, governments have established recycling schemes for CFLs and glass generally.

CFLs radiate a light spectrum that is different from that of incandescent lamps. Improved phosphor formulations have improved the perceived colour of the light emitted by CFLs, such that some sources rate the best "soft white" CFLs as subjectively similar in colour to standard incandescent lamps.[3]


An early compact fluorescent lamp

The parent to the modern fluorescent lamp was invented in the late 1890s by Peter Cooper Hewitt.[4] The Cooper Hewitt lamps were used for photographic studios and industries.[4]

Edmund Germer, Friedrich Meyer, and Hans Spanner patented a high-pressure vapor lamp in 1927.[4] George Inman later teamed with General Electric to create a practical fluorescent lamp, sold in 1938 and patented in 1941.[4] Circular and U-shaped lamps were devised to reduce the length of fluorescent light fixtures. The first fluorescent bulb and fixture were displayed to the general public at the 1939 New York World's Fair.

The helical (three-dimensional spiral) CFL was invented in 1976 by Edward Hammer, an engineer with General Electric,[5] in response to the 1973 oil crisis. Although the design met its goals, and it would have cost GE about US$25-million to build new factories to produce the lamps, the invention was shelved.[6] The design eventually was copied by others.[6] In 1995, helical lamps, manufactured in China, became commercially available;[7] their sales have steadily increased.

In 1980, Philips introduced its model SL, which was a screw-in lamp with integral ballast. The lamp used a folded T4 tube, stable tri-color phosphors, and a mercury amalgam. This was the first successful screw-in replacement for an incandescent lamp. In 1985 Osram started selling its model EL lamp, which was the first CFL to include an electronic ballast.[8]

Development of fluorescent lamps that could fit in the same volume as comparable incandescent lamps required the development of new, high-efficacy phosphors that could withstand more power per unit area than the phosphors used in older, larger fluorescent tubes.[8]


Non-integrated electronic ballast for compact fluorescent lamps

The most important technical advance has been the 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. Integrated lamps combine a tube, an electronic ballast and either an Edison screw or a bayonet fitting in a single unit. These lamps allow consumers to replace incandescent lamps easily with CFLs. Integrated CFLs work well in many standard incandescent light fixtures, reducing the cost of converting to fluorescent. Special 3-way models and dimmable models with standard bases are available.

Non-integrated CFLs have the ballast permanently installed in the luminaire, and only the lamp bulb is usually changed at its end of life. Since the ballasts are placed in the light fixture they are larger and last longer compared to the integrated ones, and they don't need to be replaced when the bulb reaches its end-of-life. Non-integrated CFL housings can be both more expensive and sophisticated. They have two types of tubes: a bi-pin tube designed for a conventional ballast, and a quad-pin tube designed for an electronic ballast or a conventional ballast with an external starter. A bi-pin tube contains an integrated starter which obviates the need for external heating pins but causes incompatibility with electronic ballasts.

Non-integrated bi-pin double-turn compact fluorescent lamp


CFLs have two main components: a gas-filled tube (also called bulb or burner) and a magnetic or electronic ballast. For their principles of operation, see Fluorescent lamp.

An electronic ballast and permanently attached tube in an integrated CFL

Standard shapes of CFL tube are single-turn double helix, double-turn, triple-turn, quad-turn, circular, and butterfly.

Electronic ballasts contain a small circuit board with rectifiers, a filter capacitor and usually two switching transistors. The incoming 50-60 Hz AC current is first rectified to DC, then converted to high frequency AC by the transistors, connected as a resonant series DC to AC inverter. The resulting high frequency, around 40 kHz or higher,[citation needed] 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.

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. There are various aid agency-led initiatives in developing countries to replace kerosene lanterns (with their associated health hazards) with DC CFLs (with car batteries and small solar panels or wind generators). [9]

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

Spectrum of light

Spectrum of a CFL bulb. The camera had a diffraction grating in front of the lens. The discrete images are produced by the different colors in the light, a line spectrum.

CFLs emit light from a mix of phosphors inside the bulb, each emitting one band of color. Modern phosphor designs balances the emitted light color, energy efficiency, and cost. Every extra phosphor added to the coating mix decreases efficiency and increases cost. Good quality consumer CFLs use three or four phosphors to achieve a "white" light with a color rendering index (CRI) of about 80, where the maximum 100 represents the appearance of colors under daylight or a black-body (depending on the correlated color temperature).

A photograph of various lamps illustrates the effect of color temperature differences (left to right):
  1. Compact Fluorescent: General Electric, 13 W, 6,500 K
  2. Incandescent: Sylvania 60 W Extra Soft White
  3. Compact Fluorescent: Bright Effects, 15 W, 2,644 K
  4. Compact Fluorescent: Sylvania, 14 W, 3,000 K

Color temperature can be indicated in kelvins or mireds (1 million divided by the color temperature in kelvins). The color temperature of a light source is the temperature of a black body that has the same chromaticity (i.e. color) of the light source. A notional temperature, the correlated color temperature, the temperature of a black body which emits light of a hue which to human color perception most closely matches the light from the lamp, is assigned.

As color temperature increases, the color changes from red to yellow to white to blue. Color names associated with a particular color temperature are not standardized for modern CFLs and other tri-phosphor lamps like they were for the older-style halophosphate fluorescent lamps. There are variations and inconsistencies between manufacturers. For example, Sylvania's Daylight CFLs have a color temperature of 3,500 K, while most other lamps called daylight have color temperatures of at least 5,000 K.

Name Color temperature
(K) (Mired)
Warm/soft white ≤ 3,000 ≥ 333
(Bright) white 3,500 286
Cool white 4,000 250
Daylight ≥ 5,000 ≤ 200

Colored CFLs are also produced, less commonly:

A blacklight CFL.

Black light CFLs, with UVA generating phosphor, are much more efficient than incandescent black light lamps.

Comparison with incandescent lamps


The rated life of a CFL ranges from 8 to 15 times that of incandescents.[10] CFLs typically have a rated lifespan of 6,000 to 15,000 hours, whereas incandescent lamps are usually manufactured to have a lifespan of 750 hours or 1,000 hours.[11][12][13]

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 turned on and off frequently. In the case of a 5-minute on/off cycle the lifespan of a CFL can be reduced to "close to that of incandescent light bulbs".[14] The U.S. Energy Star program suggests that fluorescent lamps be left on when leaving a room for less than 15 minutes to mitigate this problem.

CFLs produce less light later in their lives than when they are new. The light output decay is exponential, with the fastest losses being soon after the lamp is first used. By the end of their lives, CFLs can be expected to produce 70–80% of their original light output. [15] The response of the human eye to light is logarithmic (a photographic "f-stop" reduction represents a halving in actual light, but is subjectively quite a small change).[16] A 20–30% reduction over many thousands of hours represents a change of about half an f-stop. So, presuming the illumination provided by the lamp was ample at the beginning of its life, such a difference will be compensated for by the eyes, for most purposes.[17]

Energy efficiency

The chart shows the energy usage for different types of light bulbs operating at different light outputs. Points lower on the graph correspond to lower energy use.

CFLs uses 3–4 times less power than incandescent lamps of equivalent brightness.[18] 50%–70% of the world's total lighting market sales are incandescent.[19] Replacing all inefficient lighting with CFLs would save 409 terawatt hours (TWh) per year, 2.3% of the world's electricity consumption. In the US, it is estimated that replacing all the incandescents would save 80 TWh yearly.[20]

Electrical power equivalents for differing lamps[21]
Electrical power consumption
Watts (W)
Minimum light output
lumens (lm)
Compact fluorescent Incandescent
9–13 40 450
13–15 60 800
18–25 75 1,100
23–30 100 1,600
30–52 150 2,600

Heating and cooling

If a building's indoor incandescent lamps are replaced by CFLs, the heat produced due to lighting is significantly reduced. In warm climates or in office or industrial buildings where air conditioning is often required, CFLs reduce the load on the cooling system when compared to the use of incandescent lamps, resulting in savings in electricity in addition to the energy efficiency savings of using CFLs instead of incandescent lamps. However in cooler climates in which buildings require heating, the heating system need to replace the reduced heat from lighting fixtures. While the CFLs are still saving electricity, total greenhouse gas emissions may increase in certain scenarios, such as the operation of a natural gas furnace to replace the unintended heating from CFLs running on low-GHG electricity. In Winnipeg, Canada, it is estimated that CFLs will only generate 17% savings in energy compared to incandescent bulbs, as opposed to the 75% savings that can be expected without heating or cooling considerations.[22]

Luminous efficacy

Because the eye's sensitivity changes with the wavelength, the output of lamps is commonly measured in lumens, a measure of the power of light perceived by the human eye. The luminous efficacy of lamps is the number of lumens produced for each watt of electrical power used. A theoretical, 100%-efficient, electric light source producing light only at the wavelength to which the human eye is most sensitive would produce 680 lumens per watt.[23]

The luminous efficacy of a typical CFL is 50–70 lumens per watt (lm/W) and that of a typical incandescent lamp is 10–17 lm/W.[18] Compared to a theoretical 100%-efficient lamp (680 lm/W), these lamps have lighting efficiency ranges of 9–11% for CFLs and 1.9–2.6%, for incandescents.[23]


While the purchase price of a CFL is typically 3–10 times greater than that of an equivalent incandescent lamp, a CFL lasts 6–15 times longer and uses 3–4 times less energy. A U.S. 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."[24]

CFLs are extremely cost-effective in commercial buildings when used to replace incandescent lamps. Using average U.S. commercial electricity and gas rates for 2006, a 2008 article found that replacing each 75 W incandescent lamp with a CFL resulted in yearly savings of $22 in energy usage, reduced HVAC cost, and reduced labour to change lamps. The incremental 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 electric rates and, to a lesser extent, also in regions with higher than U.S. average cooling requirements.[25]

The current price of CFLs reflects the manufacturing of nearly all CFLs in China, where labour costs less. In September 2010, the Winchester, Virginia General Electric plant closed,[26] leaving Osram Sylvania and the tiny American Light Bulb Manufacturing Inc. the last companies to make standard incandescent bulbs in the United States.[27] At that time, Ellis Yan, whose Chinese company made the majority of CFLs sold in the United States, said he was interested in building a United States factory to make CFL bulbs, but wanted $12.5 million from the U.S. government to do so. General Electric had considered changing one of its bulb plants to make CFLs, but said that even after a $40 million investment in converting a plant, wage differences would mean costs would be 50% higher.[26]

Comparison with alternative technologies

Solid-state lighting using light-emitting diodes (LEDs) now fills many specialist niches such as traffic lights. Recent consumer availability of household LED lights now compete with CFLs for high-efficiency house lighting as well.[28] LEDs providing over 200 lm/W have been demonstrated in laboratory tests[29] and expected lifetimes of around 50,000 hours are typical. The luminous efficacy of available LED lamps does not typically exceed that of CFLs, though there have been LED lamps with 75 lm/W overall luminous efficacy at least since autumn 2009. U.S. Department of Energy (DOE) tests of commercial LED lamps designed to replace incandescent or CFLs showed that average efficacy was still about 30 lm/W in 2008 (tested performance ranged from 4 lm/W to 62 lm/W).[30] Solid-state lighting continues to improve; in June 2011 the 8 products in the A-line bulb configuration that DOE tested [31] ranged from 50 to 97 lumens per watt, with an average of 62 lumens/watt.

General Electric discontinued a 2007 development project intended to develop a high-efficiency incandescent bulb with the same lumens per watt as fluorescent lamps.[32] Meanwhile other companies have developed and are selling halogen incandescents that use 70% of the energy of standard incandescents.[33]

Other CFL technologies

Another type of fluorescent lamp is the electrodeless lamp, known as magnetic induction lamp, radiofluorescent lamp or fluorescent induction lamp. These lamps have no wire conductors penetrating their envelopes, and instead excite mercury vapour using a radio-frequency oscillator.[34] As of 2011 this type of light source was struggling with high cost of production, stability of the products produced by domestic manufacturers in China, establishing an internationally recognized standard and problems with EMC and RFI[citation needed]. Furthermore, induction lighting is excluded from Energy Star standard for 2007 by the EPA.

The cold-cathode fluorescent lamp (CCFL) is a newer form 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 document scanners and also for back-lighting LCD displays, and later manufactured for use as lamps. The efficiency (lumens per watt) is about half that of CFLs[citation needed]. 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 an effective and efficient replacement for lighting that is turned on and off frequently with little extended use (for example, in a bathroom or closet).

A few manufacturers[35][36] make CFL bulbs with mogul Edison screw bases intended to replace 250- and 400-watt metal halide lamps, claiming a 50% energy reduction; these lamps require rewiring of the lamp fixtures to bypass the lamp ballast.


Starting time

Incandescents reach full brightness a fraction of a second after being switched on, although some models take several seconds to reach their rated luminance. As of 2009, CFLs turn on within a second, but many still take time to warm up to full brightness.[37] The light color may be slightly different immediately after being turned on.[38] Some CFLs are marketed as "instant on" and have no noticeable warm-up period,[39] but others can take up to a minute to reach full brightness,[40] or longer in very cold temperatures. Some that use a mercury amalgam can take up to three minutes to reach full output.[39] This and the shorter life of CFLs when turned on and off for short periods may make CFLs less suitable for applications such as motion-activated lighting.

Hybrid CFL

In November 2010 hybrid CFLs, with instant full brightness with no warm-up delay, became available.[41][42] These lamps combine a halogen lamp with a CFL. The halogen lamp lights immediately, and is switched off once the CFL has reached full brightness.

Human health

The cost effectiveness of battery-powered CFLs allows aid agencies to support initiatives to replace kerosene lamps, whose fumes cause chronic lung disorders in typical homes and workplaces in developing nations.[9]

According to the European Commission Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) in 2008, the only property of compact fluorescent lamps that could pose an added health risk is the ultraviolet and blue light emitted. The worst that can happen is that this radiation could aggravate symptoms in people who already suffer rare skin conditions that make them exceptionally sensitive to light. They also stated that more research is needed to establish whether compact fluorescent lamps constitute any higher risk than incandescent lamps.[43]

If individuals are exposed to the light produced by some single-envelope compact fluorescent lamps for long periods of time at distances of less than 20 cm, it could lead to ultraviolet exposures approaching the current workplace limit set to protect workers from skin and retinal damage.[43]

The UV radiation received from CFLs is too small to contribute to skin cancer and the use of double-envelope CFLs "largely or entirely" mitigates any other risks.[43]

Environmental issues

Mercury content

CFLs, like all fluorescent lamps, contain mercury[44][45] as vapor inside the glass tubing. Most CFLs contain 3–5 mg per bulb, with the bulbs labeled "eco-friendly" containing as little as 1 mg.[46][47] Because mercury is poisonous, even these small amounts are a concern for landfills and waste incinerators where the mercury from lamps may be released and contribute 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.[48] In the EU the same cap is required by the RoHS law.

In areas with coal-fired power stations, the use of CFLs saves on mercury emissions when compared to the use of incandescent bulbs. This is due to the reduced electrical power demand, reducing in turn the amount of mercury released by coal as it is burned.[49][50] In July 2008 the U.S. EPA published a data sheet stating that the net system emission of mercury for CFL lighting was lower than for incandescent lighting of comparable lumen output. This was based on the average rate of mercury emission for U.S. electricity production and average estimated escape of mercury from a CFL put into a landfill.[51] Coal-fired plants also emit other heavy metals, sulphur, and carbon dioxide.

Net mercury emissions for CFL and incandescent lamps, based on EPA FAQ sheet, assuming average U.S. emission of 0.012 mg of mercury per kilowatt-hour and 14% of CFL mercury contents escapes to environment after land fill disposal.

In the United States, the U.S. Environmental Protection Agency estimated that if all 270 million compact fluorescent lamps sold in 2007 were sent to landfill sites, that this would represent around 0.13 metric tons, or 0.1% of all U.S. emissions of mercury (around 104 metric tons that year).[52]

The EPA updated their mercury comparison graph in November 2010. The graph assumes that CFLs last an average of 8000 hours regardless of manufacturer and premature breakage. In areas where coal is not used to produce energy, the content emissions would be less than the power plant emissions for both types of bulb.[53]

Broken and discarded lamps

Health and environmental concerns about mercury have prompted many jurisdictions to require spent lamps to be properly disposed or recycled rather than being included in the general waste stream sent to landfills. It is unlawful to dispose of fluorescent bulbs as universal waste in the states of California, Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin.[54] 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 U.S., The Home Depot is the first retailer to make CFL recycling options widely available.[55]

Special handling instructions for breakage are currently not printed on the packaging of household CFL bulbs in many countries. The amount of mercury released by one bulb can temporarily exceed U.S. federal guidelines for chronic exposure.[56][57] Chronic however, implies that the exposure continues constantly over a long period of time and the Maine DEP study noted that it remains unclear what the health risks are from short-term exposure to low levels of elemental mercury. The Maine DEP study also confirmed that, despite following EPA best-practice cleanup guidelines on broken CFLs, researchers were unable to remove mercury from carpet, and agitation of the carpet — such as by young children playing — created localized concentrations as high as 0.025 mg/m3 in air close to the carpet, even weeks after the initial breakage. Conventional tubular fluorescent lamps have been in commercial and domestic use since the 1930s with little public concern about their handling; these and other domestic products, such as the mercury-in-glass thermometer — now banned by many countries for medical use — contain far more mercury than modern CFLs.[58]

The U.S. Environmental Protection Agency (EPA) has published best practices for cleanup of broken CFLs, as well as ways to avoid breakage, on its web site.[59] It recommends airing out the room and carefully disposing of broken pieces in a jar. A Maine Department of Environmental Protection (DEP) study of 2008 comparing clean-up methods warns that using plastic bags to store broken CFL bulbs is dangerous because vapors well above safe levels continue to leach from the bags. The EPA and the Maine DEP now recommend a sealed glass jar as the best repository for a broken bulb.[60]

According to the Northwest Compact Fluorescent Lamp Recycling Project, because household users in the U.S. Northwest have the option of disposing of these products in the same way they dispose of other solid waste, in Oregon "a large majority of household CFLs are going to municipal solid waste". They also note the EPA's estimates for the percentage of fluorescent lamps' total mercury released when they are disposed of in the following ways: municipal waste landfill 3.2%, recycling 3%, municipal waste incineration 17.55% and hazardous waste disposal 0.2%.[61]

Mercury poisoning of Chinese factory workers

In the past decade, hundreds of Chinese factory workers who manufacture CFLs for export to first world countries were being poisoned and hospitalized because of mercury exposure. Examples include workers at the Nanhai Feiyang lighting factory in Foshan, where 68 out of 72 were so badly poisoned that they required hospitalization. At another CFL factory in Jinzhou, 121 out of 123 employees were found to have excessive mercury levels, with one employee's mercury level 150 times the accepted standard.[62]


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.[citation needed] The crushed glass and metal is stored in drums, ready for shipping to recycling factories.

Greenhouse gases

In some places, such as Quebec and British Columbia, central heating for homes is provided by the burning of natural gas, whereas electricity is primarily provided by hydroelectric or nuclear power. In such areas, heat generated by conventional electric light bulbs significantly reduces the release of greenhouse gases from the natural gas.[63] Ivanco, Karney, and Waher estimate that "If all homes in Quebec were required to switch from (incandescent) bulbs to CFLs, there would be an increase of almost 220,000 tonnes in CO2 emissions in the province, equivalent to the annual emissions from more than 40,000 automobiles."

Design and application issues

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


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

In addition to the wear-out failure modes common to all fluorescent lamps, the electronic ballast may fail, since it has a number of component parts. Ballast failures may be accompanied by discolouration or distortion of the ballast enclosure, odors, or smoke.[64] 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 modes of CFLs compared to incandescent lamps, and to develop lamps with inoffensive failure modes.[65] New North American technical standards aim to eliminate smoke or excess heat at the end of lamp life.[66]

Incandescent replacement wattage inflation

An August 2009 newspaper report described that some manufacturers claim the CFL replaces a higher wattage incandescent lamp than justified by the light produced by the CFL.[67] Equivalent wattage claims can be replaced by comparison of the lumens produced by the lamp.[68]


Dimmable integrated helical CFL that dims 2%-100%, comparable to regular light bulb dimming properties.

Only some CF lamps are labeled for dimming control. Using regular CFLs with a dimmer is ineffective at dimming, can shorten bulb life and will void the warranty of certain manufacturers.[69][Third-party source needed] Dimmable CFLs are available. There is a need for the dimmer switch used in conjunction with a dimmable CFL to be matched to its power consumption range; many dimmers installed for use with incandescent bulbs do not yield acceptable results below 40W, whereas CFL applications commonly draw power in the range 7-20W. The marketing and availability of dimmable CFLs has preceded that of suitable dimmers. The dimming range of CFLs is usually between 20% and 90%.[70][unreliable source] However, in many modern CFLs the dimmable range has been improved to be from 2% to 100%, more akin to regular lights. There are two types of dimmable CFL marketed: Regular dimmable CFLs, and "switch-dimmable" CFLs. The latter use a regular light switch, while the on-board electronics has a setting where the number of times the switch is turned on & off in quick succession sets a reduced light output mode. 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.[71] Above the 80% dim limit, the bulb will generally glow at 100% brightness. However, these issues have been addressed with the latest units and some CFLs may perform more like regular incandescent lamps. 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. Cold-cathode CFLs can be dimmed to low levels, making them popular replacements for incandescent bulbs on dimmer circuits.

Perceived coldness of low intensity CFL

When a CFL is dimmed, its colour temperature (warmth) stays the same. This is counter to most other light sources (such as the sun or incandescents) where colour gets redder as the light source gets dimmer. Emotional response testing suggests that people find dim, bluish light sources to be cold or even sinister.[citation needed] This may explain the persistent lack of popularity for CFLs in bedrooms and other settings where a subdued light source is preferred.


Some CFLs are labelled 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.[72] Current recommendations for fully enclosed, unventilated light fixtures (such as those recessed into insulated ceilings), are either to use "reflector CFLs" (R-CFL),[73][74] cold-cathode CFLs or to replace such fixtures with those designed for CFLs.[73] A CFL will thrive in areas that have good airflow, such as in a table lamp.[75]

Power quality

The introduction of CFLs may affect power quality appreciably, particularly in large-scale installations. The input stage of a CFL is a rectifier, which presents a non-linear load to the power supply and introduces harmonic distortion on the current drawn from the supply.[76][77] In such cases, CFLs with low (below 30 percent) total harmonic distortion (THD) and power factors greater than 0.9 should be used.[78][79][80]

Infrared signals

Electronic devices operated by infrared remote control can interpret the infrared light emitted by CFLs as a signal, this limits the use of CFLs near televisions, radios, remote controls, or mobile phones.[81]


Fluorescent lamps can cause window film to exhibit iridescence. This phenomenon usually occurs at night. The amount of iridescence may vary from almost imperceptible, to very visible and most frequently occurs when the film is constructed using one or more layers of sputtered metal. It can however occur in non-reflective films as well. When iridescence does occur in window film, the only way to stop it is to prevent the fluorescent light from illuminating the film.

Use with timers, motion sensors, light sensors, and other electronic controls

Some electronic (but not mechanical) timers can interfere with the electronic ballast in CFLs and can shorten their lifespan.[81] Some timers rely on a connection to neutral through the bulb and so pass a tiny current through the bulb, charging the capacitors in the electronic ballast. They may not work with a CFL connected, unless an incandescent bulb is also connected. They may also cause the CFL to flash when off. This can also be true for illuminated wall switches and motion sensors. Also, most CFLs will not work with light sensor devices, as in a "dusk to dawn" device. Cold-cathode CFLs avoid many of these problems. Timer manufacturers may make products compatible with CFLs.[citation needed]

Fire hazard

When the base of the bulb is not made to be flame-retardant, as required in the voluntary standard for CFLs, then the electrical components in the bulb can overheat which poses a fire hazard.[82]

A compact fluorescent lamp used outside of a building.

Outdoor use

CFLs are generally not designed for outdoor use and some 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).[83] Light output drops at low temperatures.[84] Cold-cathode CFLs will start and perform in a wide range of temperatures due to their different design.

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 colour temperature.

Lifetime brightness

Fluorescent lamps get dimmer over their lifetime,[85] so what starts out as an adequate luminosity may become inadequate. In one test by the U.S. Department of Energy of "Energy Star" products in 2003–04, one quarter of tested CFLs no longer met their rated output after 40% of their rated service life.[86][87]

Ultraviolet (UV) emissions

Fluorescent bulbs can damage paintings and textiles which have light-sensitive dyes and pigments. Strong colours will tend to fade on exposure to UV light. Ultraviolet light can also cause polymer degradation with a loss in mechanical strength and yellowing of colourless products.[88]

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 that do not meet energy efficiency requirements.

In 2008, the European Union approved regulations progressively phasing out incandescent bulbs starting in 2009 and finishing at the end of 2012. By switching to energy saving bulbs, EU citizens will save almost 40 TW·h (almost the electricity consumption of 11 million European households), leading to a reduction of about 15 million metric tons of CO2 emissions per year.[89]

Australia, Canada, and the United States have also announced plans for nationwide efficiency standards that would constitute an effective ban on most current incandescent bulbs.[90][91][92]

Venezuela and Cuba have launched massive incandescent light bulbs replacement programs in order to save energy. In the case of Venezuela, the government was able to save 2000 MW of electricity in the first six months of the 2006 program called Mission Energy Revolution, which by 2007 replaced 20 million incandescent light bulbs with CFL from a total of an estimated 55 million light bulbs in the country. Cuba replaced all the 11 million light bulbs used on the island.[93] Also, Venezuela signed an agreement with Vietnam, one of the largest producers of CFLs in the world, to establish a factory to supply the future demand and hand-outs of government light bulbs.[94]

The United States Department of Energy reports that sales of CFLs have dropped between 2007 and 2008, and estimated only 11% of suitable domestic light sockets use CFLs.[95][96]

In the United States, the Program for the Evaluation and Analysis of Residential Lighting (PEARL) was created to be a watchdog program. PEARL has evaluated the performance and ENERGY STAR compliance of more than 150 models of CFL bulbs.[97][98]

Labeling programs

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.[99] 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 the light.[100]

In the United Kingdom a similar program is run by the Energy Saving Trust to identify lighting products that meet energy conservation and performance guidelines.[101]

Notes and references

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