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.[2] 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.[3]
History
The parent to the modern compact fluorescent lamp (CFL) 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 then 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] 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.[5] The design was eventually leaked out and copied by others.[5]
Construction
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.
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, 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.[6]
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.[7][8]
The ballasts make these light fixtures relatively expensive. They cost anywhere from $85 to $200 USD for each recessed light fixture. If a ballast with dimming capabilities is desired the cost is anywhere from $125 to $300 USD per recessed light fixture. 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.
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