Fluorescent lamps are low pressure or low intensity discharge lamps. The lamp consists of a closed tube that contains two cathodes, an inert gas such as argon, and a small amount of mercury. Typically the glass tube is filled with a mixture of argon and mercury vapor. The metal electrodes are coated with an alkaline-earth oxide. When voltage is supplied to the lamp in the correct amount, an electrical arc strikes between the two cathodes. This arc emits energy that the phosphor coating on the lamp tube converts into usable light. Commonly used phosphor coatings are zinc silicate and magnesium tungstate.
The fluorescent lamp was first introduced to the public at the New York World's Fair in the late thirties (1937). The lamps were introduced commercially in about 1938. The fluorescent lamp is a low pressure gas discharge source, in which the light is produced predominantly by fluorescent powders activated by ultraviolet energy generated by a mercury arc. Typically, a fluorescent lamp must efficiently generate 253.7 millimicron ultraviolet radiation to excite the phosphors coating the inside of the tubular glass bulb. The lamp is usually in the form of a long tubular bulb with an electrode sealed at each end.
The modern fluorescent lamp has an efficacy of approximately 65-80 lumens per watt. Today fluorescent lamps are also available in circular and 'folded' shapes. Lamps with various different color temperatures and color rendering properties are commonly available. The most common fluorescent lamp is the CW or cool white version, although new 'warmer' versions are now gaining popularity, worldwide. All fluorescent lamps require a ballast, for operation. A fluorescent lamp tube has argon combined with a minuscule amount of mercury. At the low pressure within the lamp, becomes mercury vapor, even at temperatures only slightly above room ambient. An electrical discharge ionizes the mercury vapor, which emits UV radiation. The UV radiation stimulates phosphors that coat the interior of the lamp's glass envelope, and the phosphors convert essentially all of the UV radiation to visible light.
The conversion of electrical energy to light is much more efficient than in an incandescent lamp, and a considerably smaller fraction of the input energy is converted to heat. Generally fluorescent fixings give out ~ 3 times as much light/watt as a halogen. The color of the light that a fluorescent lamp produces depends on the composition of the lamp's phosphors. Fluorescents used for general lighting purposes are nearly enoughentirely of "hot cathode" type. The mechanism for conducting electronsfrom the negative electrode to gas/vapor is "thermionic arc". The negative end of the arc, even though it is much more distended than awelding arc due to the low gas/vapor pressure, heats the electrode to atemperature such that molecules in a coating on the electrode lose theirgrip on some of their electrons. Hot cathode fluorescents are generally near or a bit over 100 mA in their smallest sizes (one popular one may oftenwork reasonably at 60 mA) and the usual sizes take generally around 220-450 mA and a few take more.
The most typical fluorecent lamp type seen in Europe is offices and homes is lamp where there is is one fluorescent bulb (or sometimes two in series) wired in series with a magnetic ballast that limit the current though the lamp to the needed range. In addition to this there is also the starter (passes power for some time though tube heaters when bulb is turned on) and usually some kind of filter capacitor (for RFI filtering and/or power phase compensation). This construction is simple and works well with mains voltages used in 220-240V countries. There the voltage is well enough for the tube to start conducting reliably and there is enough voltage range for the simple magnetic ballast work well (the tube voltage is something in 60-100V when it is on). The simplest sort of ballast, generally referred to as a magnetic ballast, works something like an inductor. It is sufficient for fluorescent lamps operating at around 230V AC or higher voltage. Different lamps require specialized ballasts designed to maintain the specific voltage and current levels needed for varying tube designs. Magnetic ballasts modulate electrical current at a relatively low cycle rate, which can cause a noticeable flicker. Magnetic ballasts may also vibrate at a low frequency. This is the source of the audible humming sound people associate with fluorescent lamps.
At countries that use 110V mains voltage this simple approach does not work, because that voltage is too low for reliably opeating a fluorescent lamp directly with simple ballast. In 110V world the fluorescent lamps need to use a more complex ballast that steps-up the voltage for the bulb to initially reliably start. This kind of ballast is much more complicated, more expensive and less energy efficient than the simple "just coil" ballast. Many fluorescent lamps operating at 110V AC nowadays use electronic ballasts that can properly power the lamp from 110V power supply with better efficiency than magnetic ballast and are not too much more expensive than those complicated magnetic ballasts. Modern ballast designs use advanced electronics to more precisely regulate the current flowing through the electrical circuit. Since they use a higher cycle rate, you don't generally notice a flicker or humming noise coming from an electronic ballast.
In many office building and similar places there are also fluorescent lamps that operate at higher voltages than 110V in USA and Canada. In those buildings there are usually higher voltage three-phase power in use within the ouse for power distribution. In many places the fluorescent lamps are powered with 277V AC or 347V AC that is derived from higher voltage three-phase power system (between phase wires or between phase and neutral). At those higher voltages the simple magnetic ballast lamps work well. In such building using higher voltage for lighting saves money.
In a cold cathode fluorescent lamp as well as neon glow lamps, the cathode mechanism is "glow discharge". This is a multilayer processbut in this process positive ions of the active gas/vapor ingredient(s)accelerate towards the electrode and knock electrons from atoms of theelectrode material to permit conduction from the electrode material to thegas/vapor. This is more practical and has longer life than hot cathode with lowercurrents. Miniature cold cathode fluorescent lamps have typical operatingcurrent often around 5 mA. "Neon signs" are cold cathode and frequentlyfluorescent and usually operate at 20 mA. There is a large style of coldcathode fluorescent (rare) with operating current somewhere around ormaybe a little over 100 mA. One advantage of cold cathode fluorescent is a lack of extra wear from starting. The disadvantage of glow discharge over thermionic arc is that glowdischarge has a much higher voltage drop in the cathode process (typically 55-80 volts) compared to usually 8-12 volts for thermionic arc. Cold cathode fluorescent lamps can be for example seen in applications like neon lights as used for advertisements and for example as miniature back-lights as used in laptop computer LCD screend.
Cold-cathode fluorescent tube (CCFT) / Cold-cathode fluorescent lamp (CCFL) is a special form of fluorescent tube without heaters on the cathodes. CCFL is often used as a backlight in LCD flat panel displays and also in some decorative lighting applications (for example decorating PC cases). CCFL bulbs are typically small (typical diameter 3-10 mm, lenght 10-30 cm). CCFT requires an adjustable, current-limited, high-voltage, ac-power source. Generally the tube needs quite high voltage to start operate and then operates at lower voltage (up to several hundred volts). EMI and tube-lifetime considerations practically dictate a sinusoidal waveform to be used for powering CCFT. There are also some large cold-cathode fluorescent tube systems that use high voltage mains powered transformer capable of putting out high voltage at current of around 100 mA.
Note on installing fluoresent light fixtures: Many mains powered florescent fixtures need to be grounded to work properly. Two wire fixtures might need the correct wire connected to the neutral and hot. If they are reversed, they will be hard to start. That you can touch yours andhave them start indicates you may indeed have a reversed hot andneutral.
Developed in the late 1980's the compact fluorescent lamp revolutionized the lighting industry. This lamp (also referred to as the PL lamp), is simply a folded fluorescent tube, sometimes no larger than a standard 'light bulb'. The ballast is usually mounted in the base pf the lamp. This new lamp allows most household incandescent lamps to be replaced with these new energy saving fluorescent lamps. PL lamps are available in various wattages from approximately 9 - 50 watts, and are available from all major lamp manufacturers. Compact fluorescent light bulbs, or CFLs, use fluorescent light technology in a compact size that can be used in place of standard light bulbs. Compact fluorescent light bulbs use 70 percent less energy than standard incandescent light bulbs. Roughly, roughly, a compact fluorescent lamp produces as much light as an incandescent lamp of 3-4 times as much wattage. Good compact fluorescents normally produce 4 times as much light as good incandescents, except compact fluorescents can be dimmed by non-ideal temperatures, heat buildup in fixtures, etc. CFLs come in a variety of sizes, depending on wattage and manufacturer, and will fit most standard lighting fixtures. CFLs last an average of 10,000 hours, compared to only 850 hours for a standard incandescent light bulb. Generally you can replace a norma light bulb in the fixture with a compact fluorescent lamp that mechanicaly fits to the lamp in most cases. Be prepared though that if you put a compact fluorescent in a fixture designed for an incandescent, the light may not be distributed in a less favorable manner than that of the incandescent. Some lamp fixture work better than other with compact fluorescent bulbs.
Fluorescent lamps and incandescent lamps can vary significantly in efficiency with manufacturer and model due to various issues of design and quality. "Standard" fluorescents of the more usual "shades of white", especially the 4 foot T8 (1 inch diameter) ones, are a little more efficient than compact fluorescents. Compact fluorescents with magnetic ballasts are usually less efficient than ones with electronic ballasts and they also have quality issues. Non-compact fluorescents also suffer from ballast issues.
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