A compact fluorescent lamp ( CFL ), also known as a compact fluorescent light or energy saving light (or less commonly as a compact fluorescent tube ), is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit into most existing light fixtures formerly used for incandescents.
Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power, have a longer rated life, but have a higher purchase price. In the United States, a CFL can save over 30 US$ in electricity costs over the lamp's life time compared to an incandescent lamp, and save 2,000 times its own weight in greenhouse gases. Like all fluorescent lamps, CFLs contain mercury, which complicates their disposal.
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 some sources rate the best 'soft white' CFLs as subjectively similar in color to standard incandescent lamps.
History
The parent to the modern fluorescent lamp 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 Edward E. 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. CFLs have steadily increased in sales volume.
Construction
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.
Parts
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 (mercury vapour), 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.
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 many standard incandescent light fixtures, which lowers the cost of CFL conversion. 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. These ballasts are typically of the magnetic type, and the starter is housed in the base of the replaceable bulb. 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.
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.
Health issues
See also: Light sensitivityAccording 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 by such devices. 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.
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.
The UV received from CFLs is too small to contribute to skin cancer and the use of double-envelope CFL lamps "largely or entirely" mitigates any other risks, they say.
Comparison with incandescent lamps
Lifespan
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 "close to that of incandescent light bulbs". The US 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 life 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. 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 20 to 33 percent 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 a building's indoor incandescent lamps are replaced by CFLs, the heat produced due to lighting will be reduced. At times when the building requires both heating and lighting, the heating system will make up the heat. If the building requires both illumination and cooling, then CFLs also reduce the load on the cooling system compared to incandescent lamps, resulting in two concurrent savings in electrical power.
Efficacy and efficiency
For more details on this topic, see Luminous efficacy.A typical CFL is in the range of 17 to 21% efficient at converting electric power to radiant power based on 60 to 72 lumens per watt source efficacy, and 347 lumens per radiant watt luminous efficacy of radiation for a tri-phosphor spectrum. Because the eye's sensitivity changes with the wavelength, the output of lamps is commonly measured in lumens, a measure that accounts for the effect of the source's spectrum on the eye. The luminous efficacy of CFL sources is typically 60 to 72 lumens per watt, versus 8 to 17 lm/W for incandescent lamps.
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