Fluorescent light lamps technology (CFL).
Fluorescent light lamp are known also as CFL. They have a realy controversial life. Some people like them some say they are worse than the old ones. What do you think?
A compact fluorescent lamp (CFL), also known as a compact fluorescent light or energy saving light (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 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. 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.
The fundamental of CFL
The fundamental means for conversion of electrical energy into radiant energy in a fluorescent lamp relies on inelastic scattering of electrons. An incident electron collides with an atom in the gas. If the free electron has enough kinetic energy, it transfers energy to the atom's outer electron, causing that electron to temporarily jump up to a higher energy level. The collision is 'inelastic' because a loss of energy occurs.
This higher energy state is unstable, and the atom will emit an ultraviolet photon as the atom's electron reverts to a lower, more stable, energy level. Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum predominantly at wavelengths of 253.7 nm and 185 nm. This is not visible to the human eye, so must be converted into visible light. This is done by making use of fluorescence. Ultraviolet photons are absorbed by electrons in the atoms of the lamp's fluorescent coating, causing a similar energy jump, then drop, with emission of a further photon. The photon that is emitted from this second interaction has a lower energy than the one that caused it. The chemicals that make up the phosphor are chosen so that these emitted photons are at wavelengths visible to the human eye. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon goes to heat up the phosphor coating.
The efficiency of fluorescent lighting owes much to the fact that low pressure mercury discharges emit about 65% of their total light in the 254 nm line (another 10–20% of the light is emitted in the 185 nm line). The UV light is absorbed by the bulb's fluorescent coating, which re-radiates the energy at longer wavelengths to emit visible light. The blend of phosphors controls the color of the light, and along with the bulb's glass prevents the harmful UV light from escaping.
When the light is turned on, the electric power heats up the cathode enough for it to emit electrons. These electrons collide with and ionize noble gas atoms in the bulb surrounding the filament to form a plasma by a process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp.
Construction Close-up of the cathodes and anodes of a germicidal lamp (an essentially-similar design that uses no fluorescent phosphor, allowing the electrodes to be seen.)
A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor and argon, xenon, neon, or krypton. The pressure inside the lamp is around 0.3% of atmospheric pressure. The inner surface of the bulb is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The bulb's cathode is typically made of coiled tungsten which is coated with a mixture of barium, strontium and calcium oxides (chosen to have a relatively low thermionic emission temperature).
Fluorescent lamp tubes are typically straight and range in length from about 100 millimeters (3.9 in) for miniature lamps, to 2.43 meters (8.0 ft) for high-output lamps. Some lamps have the tube bent into a circle, used for table lamps or other places where a more compact light source is desired. Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, three, or four, or a small diameter tube coiled into a spiral, to provide a high amount of light output in little volume.
Light-emitting phosphors are applied as a paint-like coating to the inside of the tube. The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary; large grains, 35 micrometres or larger, lead to weak grainy coatings, whereas too many small particles 1 or 2 micrometres or smaller leads to poor light maintenance and efficiency. Most phosphors perform best with a particle size around 10 micrometres. The coating must be thin enough to capture all the ultraviolet light produced by the mercury arc, but no so thick that the phosphor coating absorbs too much visible light. The first phosphors were synthetic versions of naturally-occuring fluorescent minerals, with small amounts of metals added as activators. Later other compuonds were discovered, allowing differing colors of lamps to be made.
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