Fluorescent light fixture
A fluorescent luminaire is known as the set made up of a lamp, called a fluorescent tube, and a frame, which contains the accessories necessary for its operation. In certain places, only the lamp is known as a luminaire. The lamp is a low-pressure mercury vapor discharge lamp and is normally used for domestic or industrial lighting. Its advantage over other types of lamps, such as incandescents, is its energy efficiency.
The lamp consists of a thin glass tube lined on the inside with various chemical compounds called phosphors, although they generally do not contain the chemical element phosphorus and should not be confused with it. These chemical compounds emit visible light when receiving ultraviolet radiation. The tube also contains a small amount of mercury vapor and an inert gas, usually argon or neon, at a pressure lower than atmospheric pressure. At each end of the tube is a filament made of tungsten, which when red-hot contributes to the ionization of gases.
History
The oldest antecedent of fluorescent lighting is possibly the experiment carried out and described in 1707 by Francis Hauksbee, who generated by electrostatic ionization of mercury vapor a bluish light that was enough to read a writing. Subsequently, the German physicist Heinrich Geissler built in 1856 a device by which he obtained light with a bluish glow from a rarefied gas enclosed in a tube and excited with an electric discharge. Because of its shape, this device came to be called the "Geissler tube." At the 1893 World's Fair, fluorescent devices developed by Nikola Tesla were shown.
In 1891, American inventor Daniel McFarlane Moore, a collaborator of Tesla, began experimenting with gas discharge tubes. He thus created in 1894 the "Moore lamp", which was a commercial lamp that competed with the incandescent light bulbs invented by his former boss Thomas Alva Edison. These lamps, containing nitrogen and carbon dioxide, gave off white and pink light respectively, and were moderately successful. In 1904, the first of these lamps were installed in a warehouse in the American city of Newark. As the installation, maintenance and repair work of these lamps was difficult, they were not successful.
In 1901, Peter Cooper Hewitt demonstrated his mercury-vapor lamp, which gave off blue-green light that was unsuitable for most practical uses. However, its design was very close to that of current lamps, in addition to having greater efficiency than its incandescent counterparts.
In 1926, Edmund Germer, Friedrich Meyer, and Hans Spanner proposed increasing the gas pressure inside the tube and coating it internally with a fluorescent powder that would absorb the ultraviolet radiation emitted by a gas in a plasma state, and convert it into a light more uniform white. The idea was patented the following year and the patent was later acquired by the American company General Electric and under the direction of George E. Inman it was ready for commercial use in 1938. The well-known straight tubes and preheat ignition were They were first shown to the public at the New York World's Fair in 1939. Since then, the operating principles have remained unchanged, except for the manufacturing technologies and raw materials used, which has resulted in lower prices and has contributed to popularize these lamps throughout the world.
Operation
With starter and reactance
It is an operating system that is falling into disuse since the appearance of electronic devices that perform the same function in a better way and with less energy consumption. It is described, however, because many such luminaires still exist and will continue to exist for quite some time, although new ones are now rarely installed. The European Union, promoting energy saving, requires that the ballasts of these luminaires be more efficient every day, and this can only be achieved with electronic ballasts. Regulation (CE) No. 245/2009 of the commission of March 18, 2009 provided for the total prohibition of this type of ballasts, and even some of the less efficient electronic ones, as of 2017, but in regulation 347 /2010 has limited this provision to the prohibition of the least efficient models.
In the figure above, apart from the lamp itself, two fundamental elements can be distinguished: the «starter» (also called «starter» or «starter») and the «reactance» or «ballast», which provides inductive reactance. In some Spanish-speaking countries, its English synonyms starter and ballast are still used.
The primer, starter or starter is made up of a small glass vial containing low-pressure gases (neon, argon and mercury gas) and inside which there is a contact formed by a bimetallic sheet folded in "U". In parallel with this contact there is a capacitor intended for the double effect of acting as a spark absorber or spark arrestor, and of absorbing radio frequency radiation that could interfere with radio, TV or communications receivers. The presence of this capacitor is not essential for the operation of the fluorescent tube, but it helps a lot to increase the useful life of the contact of the bimetallic pair when it is subjected to work with high currents and high voltages. Both the starter and the luminaire shorten their useful life the more times it is turned on, for this reason it is recommended to use fluorescent lighting in continuous regimes and not as intermittent lighting.
The element that provides inductive reactance is called “ballast” or “ballast”, although in some countries it is incorrectly called “reactance”, which is actually the name of the electrical magnitude it provides, not of the element. Technically it is a reactor that is made up of a coil of enameled copper wire, wound on a core of iron sheets or electrical steel. The term ballast should not be confused with its namesake, the material used in the construction of railways.
When the supply voltage is applied, the gases contained in the primer bulb are ionized, which increases their temperature enough for the bimetallic sheet to deform, make contact, closing the circuit, which will cause the filaments of the ends of the tube become red hot, and this begins the ionization of gases in the proximity of the filaments. When the contact is closed, the primer turns off and its gases cool down again, so that a couple of seconds later the contact opens again. This opening results in the magnetic field created in the inductive reactance abruptly disappearing, which results in, in accordance with Faraday's induction law, the generation of a high voltage peak (self-induction) that ends up ionizing the gases. Conductive plasma is formed inside the entire fluorescent tube and, therefore, a current of electrons passes through it, which interacts with the Hg, Ar and Ne atoms, exciting them, which will emit light when de-excited, mainly in the ultraviolet region (UV).
The potential difference applied to the filaments and the tube is pulsating, because the electrical voltage that feeds the circuit is alternating current of 50 Hz (in Europe,...) or 60 Hz (in the USA, Japan,...). The filaments have thermal inertia, but the plasma does not, which causes rapid flickering in the emitted light, which can annoy some people, cause headaches and even seizures in those with epilepsy. This phenomenon is minimized by arranging the tubes in groups, each tube fed from different phases and with strobe dispersion grids. This effect is eliminated with modern electronic ballasts.
The filaments, when heated, give off electrons that, together with the self-induction peak, ionize the gases that fill the tube; This forms a plasma that conducts electricity. This plasma excites the mercury vapor atoms which, when de-excited, emit visible and ultraviolet light. These filaments are covered by a kind of powder called TRIPLECARBONATE, this is used to promote the jump of electrons between the cathode and the anode and every time the fluorescent tube is energized, a small amount of the filament is released, which forms the black spot. which is seen in fluorescent tubes when they are close to completing their useful life, once the triple carbonate in the filaments has been exhausted, there is no way for the electrons to jump and therefore the fluorescent tube stops working, despite that all other parts of the tube are in perfect condition. That is why the use of this technology is not recommended in places where it is constantly turned on and off.
The inner lining of the lamp has the function of filtering and converting ultraviolet light into visible light. The coloration of the light emitted by the lamp depends on the material of that internal coating. The tube material, common glass, helps reduce UV light that might escape outside the fixture.
Fluorescent lamps are devices with a negative slope of their electrical resistance, with respect to electrical voltage. This means that the greater the current that passes through them, the greater the degree of ionization of the gas and, therefore, the lower the resistance it opposes to the passage of said current. Thus, if the lamp is directly connected to a practically constant voltage source, such as the one supplied by the electrical network, the intensity will tend to very high values, and the lamp will be destroyed in a few seconds. To avoid this, it is always connected through a current limiting element to keep it within its working limits. This imitating element, in the case of the installation in Figure 1, is the ballast that provides inductive reluctance, which will absorb the difference between the power supply voltage and the working voltage of the tube.
Finally, the decrease in the internal resistance of the tube once ignited, causes the voltage between the starter terminals to be insufficient to ionize the gas contained in its ampoule and therefore the metallic contact remains inactive when the tube is ignited.
Until about 1975, electricity supply to homes coexisted in Argentina through alternating current and direct current, both 220 volts. Due to this, in this country a type of direct current ballast was invented around 1950 that took advantage of the negative resistance of the ionized gases of the luminaire to generate an oscillation by relaxation of a frequency of a few kHz. The primer or starter effect was achieved with a noisy system of vibrating contacts that stopped as soon as the tube was ignited. It had the drawback that from time to time the polarity had to be reversed so that the wear of the luminaire was the same in both filaments.
Compensation in fluorescent lamps
The fluorescent tube-ballast-starter assembly has reactive elements (coil and capacitors) that consume and release reactive power respectively (the coil consumes it, the capacitors release it). A capacitor is often inserted between the input terminals to allow the power factor of the device to be close to 1. This type of compensation is called "parallel compensation" because of this arrangement.
The following calculation allows us to know the value (in pico or nanofarads) of the capacitor that must be inserted, since if one of a higher value than necessary is placed, the current and its consumption will increase, so it is important to find the right one.
- C=P(So... φ φ i− − So... φ φ f)2π π fV2{displaystyle C={frac {P(tan {varphi _{i}}}-tan {varphi _{f}}})}{2pi fV^{2}}}}}}}}}}
where:
- C{displaystyle C} is the capacitance of the capacitor.
- P{displaystyle P} is the active power absorbed by the set.
- φ φ i{displaystyle varphi _{i}} is the angle whose cosine is the initial power factor, before the compensation.
- φ φ f{displaystyle varphi _{f}} is the angle whose cosine is the final power factor, after the compensation.
- V{displaystyle V} It's the input voltage.
- f{displaystyle f} is the frequency in hertz of the input voltage.
Example: If a tube is 18 W, with f = 50 Hz, V = 230 V (CA) and with final power factors of 0.85 and initial power factors of 0.226, the capacitor to use must be 4 μF (microfarads).
With electronic ballast
There is currently another type of ballast or reactor, the electronic ballast, which consists of an electronic circuit and a small coil with a ferrite core. This ballast, unlike the inductive ballast, connects to the fluorescent without a starter and achieves instant start of the lamp without appreciable flicker, or in other models, starts in a softer way. Actually, it is not a reactor in the strict sense of the term, but an electronic circuit with semiconductors that generates:
- two low tensions to light the filaments of the ends.
- a high voltage of high frequency (ten kHz) applied between the ends.
Both processes add their effects to ionize the gases and thus produce the conductive plasma that will generate the UV radiation. As a general rule, the tubes that use the electronic ballast have a significantly higher light output, and a much longer average life than those that use the inductive one.
Their connections are very simple:
- The phase cable and the neutral connect both directly to the two bullet inputs.
- In this scale there are two pairs of outputs, and each pair must connect to each end (filment) of the lamp.
As stated at the beginning, the "phosphorus" The element mentioned in the drawing below is not the chemical element called that, but a compound chemical substance, which usually does not contain phosphorus.
On
Fluorescent lamps need a few moments to warm up before reaching their normal luminous flux, so it is advisable to use them in places where they are not constantly turning on and off (such as corridors and stairs). On the other hand, as has been said, constant switching on and off significantly shortens its useful life.
The life condition of the fluorescent lamp may vary depending on its use and the environmental conditions it is in, and can be set between 5,000 and 10,000 hours.
With the aforementioned ballast or electronic ballast, replacing the traditional ballast and the primer, the tube ignition is instantaneous, thus extending its useful life. It always takes a while to reach its normal luminosity anyway.
Properties
- Luminousity: fluorescent lamps have a luminous performance that can be estimated at between 50 and 90 lm/W (lights per watt). The lightness of the lamp depends not only on the luminescent coating, but on the emitting surface, so that when the power varies the size, for example, that of 18 W measures about 60 cm, that of 36 W, 1,20 m, and that of 54 W 1,80 m.
- Useful Life: is also much greater than that of incandescence lamps, which can easily vary between 5000 h and more than 75 000 h (between 5 and 75 times more than a bulb), which depends on various factors, such as the type of fluorescent lamp or the equipment of the luminaire used with it.
- Color: There are different models in the market with different color temperatures. It is usually between 3000 K and 6500 K (from cold white to warm day). However, tubes with a wide range of color temperature can be obtained at present, which allows to find relatively easily models ranging from 2700 K to 10 000 K, recommending the choice based on the use and illuminance to be installed. The high color temperature lamps (e.g. the white color 5000 K) are recommended when you need a good color reproduction or with high illuminances; on the contrary, with low illuminances or when looking for warm colors, you will choose a low color temperature.
Advantages
Power consumption
The great advantage of this type of lamps is their relatively low energy consumption, since they have a performance between 50 and 80 lm/W (lumens per watt of power), compared to traditional incandescent lamps (between 10 and 15 lm/W), that its consumption is higher and, even, compared to other types of lamps, except the most recent ones. This has led to a very extensive use, especially in buildings for public use and offices, but consumption involves not only the lamp itself, but also the luminaire and the ignition system. Any reactance and starter ballast consumes more than its electronic counterpart, so there are possibilities of energy savings just by changing the ballast for a more modern one, a change that also eliminates other drawbacks such as flickering and delayed ignition.
Blink
Fluorescent lamps, with the ballast and starter ignition system, do not give a continuous light, but show a flicker that depends on the frequency of the alternating current applied. This is not very noticeable to the naked eye, but continuous exposure to this light can give you a headache. The effect is the same as setting a computer monitor to 52 Hz.
This flickering can cause strobing, so an object spinning at a certain speed might look static under fluorescent lighting. Therefore, in some places (such as workshops with machinery) this light may not be recommended.
Flickering, although barely perceptible, can significantly affect the health of some people with some types of migraines, epilepsy, and in some cases, its effect is so devastating to health that some people are completely excluded from some public settings (libraries, work, sports, etc.) in which this type of lighting is usually used.
Flicker also causes problems with video cameras, since the frequency at which the sensor reads the image can match fluctuations (oscillations) in intensity of the fluorescent lamp.
However, with an electronic ballast there is no such problem, since this device converts the frequency of the current from 50 or 60 Hz to 20 kHz and the flicker is not noticeable more than in a normal incandescent lamp.
Shelf Life
The life of fluorescent lamps is greatly reduced if they are turned on and off frequently, since turning them on is much more work than keeping them on.
Old-ballasted fluorescent lamps cannot be connected to a normal dimmer or dimmer (a regulator to control brightness). There are special lamps (4-contact) and special drivers that allow you to use a switch with a dimmer.
Since the mid-80s, there is a solution to avoid these drawbacks, which is the electronic ballast, which has gained great importance from the mid-90s. In this system, the tube is made to work with the same so that in the traditional way but this time at a frequency of more than 20 kHz, which completely avoids the stroboscopic effect, makes the flicker invisible to the human eye (and in turn, that video cameras hardly manage to capture it), and that noises disappear due to working above the audible spectrum. In short, an improvement of 10% is obtained in the performance of the lamp, lower consumption, less dissipated heat, absolute silence of the reactance and longer useful life for the tubes.[citation required ]
Its wavelength before being captured by the phosphor is approximately 250 to 370 nm (nanometers), within the UV spectrum.
Disadvantages
It should be taken into account that these types of lamps (fluorescent) are considered hazardous waste due to their mercury vapor content that causes mercury poisoning, so they must be disposed of properly to avoid negative environmental effects. Normally, in Europe, there are collection points in most supermarkets, and it is very important to deposit them without breaking them, because the most dangerous thing is their mercury vapor content. The vapor induces mercury poisoning when inhaled.
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