halogen lamp
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A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an
incandescent lamp An incandescent light bulb, also known as an incandescent lamp or incandescent light globe, is an electric light that produces illumination by Joule heating a filament until it glows. The filament is enclosed in a glass bulb that is eith ...
consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an
inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Though inert gases have a variety of applications, they are generally used to prevent u ...
and a small amount of a
halogen The halogens () are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would ...
, such as
iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...
or
bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...
. The combination of the halogen gas and the
tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...
filament produces a halogen-cycle chemical reaction, which redeposits evaporated tungsten on the filament, increasing its life and maintaining the clarity of the envelope. This allows the filament to operate at a higher temperature than a standard incandescent lamp of similar power and operating life; this also produces light with higher luminous efficacy and color temperature. The small size of halogen lamps permits their use in compact optical systems for
projector A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer type ...
s and illumination. The small glass envelope may be enclosed in a much larger outer glass bulb, which has a lower temperature, protects the inner bulb from contamination, and makes the bulb mechanically more similar to a conventional lamp. Source has illustrations of various double-envelope halogen bulbs. Standard and halogen incandescent bulbs are much less efficient than LED and
compact fluorescent lamp A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incan ...
s, and therefore have been or are being phased out in many places.


History

A carbon filament lamp using
chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
to prevent darkening of the envelope was patented by Edward Scribner of the US Electric Lighting Co. in 1882, and chlorine-filled "NoVak" lamps were marketed in 1892. The use of iodine was proposed in a 1933 patent which also described the cyclic redeposition of tungsten back onto the filament. In 1959,
General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...
patented a practical lamp using iodine.


Phase-out

In 2009, the EU and other European countries began a phase-out of inefficient bulbs. The production and importation of directional mains-voltage halogen bulbs was banned on 1 September 2016, and non-directional halogen bulbs followed on 1 September 2018.
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
banned some halogen light bulbs above 10W from September 2021 in favour of eco-halogen bulbs, later than the planned date of September 2020 to keep the policy in line with the European Union. In June 2021, the UK government also announced plans to end the sale of halogen light bulbs from September, as part of the UK's wider efforts to tackle
climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.


Halogen cycle

In ordinary incandescent lamps, evaporated tungsten mostly deposits onto the inner surface of the bulb, causing the bulb to blacken and the filament to grow increasingly weak until it eventually breaks. The presence of the halogen, however, sets up a reversible chemical reaction cycle with this evaporated tungsten. The halogen cycle keeps the bulb clean and causes the light output to remain almost constant throughout the bulb's life. At moderate temperatures, the halogen reacts with the evaporating tungsten, the halide formed being moved around in the inert gas filling. At some point, however, it will reach higher temperature regions within the bulb where it then dissociates, releasing tungsten back onto the filament and freeing the halogen to repeat the process. However, the overall bulb envelope temperature must be significantly higher than in conventional incandescent lamps for this reaction to succeed: it is only at temperatures of above on the inside of the glass envelope that the halogen vapor can combine with the tungsten and return it to the filament rather than the tungsten becoming deposited on the glass. A 300-watt tubular halogen bulb operated at full power quickly reaches a temperature of about , while a 500-watt regular incandescent bulb operates at only and a 75-watt regular incandescent at only . The bulb must be made of fused silica (quartz) or a high-melting-point glass (such as aluminosilicate glass). Since quartz is very strong, the gas pressure can be higher which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and so luminous efficacy) for the same average life. The tungsten released in hotter regions does not generally redeposit where it came from, so the hotter parts of the filament eventually thin out and fail. Quartz iodine lamps, using elemental iodine, were the first commercial halogen lamps launched by GE in 1959. Quite soon, bromine was found to have advantages, but was not used in elemental form. Certain hydrocarbon bromine compounds gave good results. Regeneration of the filament is also possible with fluorine, but its chemical reactivity is so great that other parts of the lamp are attacked.Burgin and Edwards Lighting Research and Technology 1970 2.2. 95–108 The halogen is normally mixed with a
noble gas The noble gases (historically the inert gases, sometimes referred to as aerogens) are the members of Group (periodic table), group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and, in some ...
, often
krypton Krypton (from 'the hidden one') is a chemical element; it has symbol (chemistry), symbol Kr and atomic number 36. It is a colorless, odorless noble gas that occurs in trace element, trace amounts in the Earth's atmosphere, atmosphere and is of ...
or
xenon Xenon is a chemical element; it has symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
. The first lamps used only tungsten for filament supports, but some designs use
molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
– an example being the molybdenum shield in the H4 twin filament
headlight A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term for t ...
for the European Asymmetric Passing Beam. For a fixed power and life, the luminous efficacy of all incandescent lamps is greatest at a particular design voltage. Halogen lamps made for 12 to 24 volt operation have good light outputs, and the very compact filaments are particularly beneficial for optical control (see picture). The ranges of multifaceted reflector "MR" lamps of 20–50 watts were originally conceived for the projection of
8 mm film 8 mm film is a motion picture film format in which the film strip is wide. It exists in two main versions – the original standard 8 mm film, also known as regular 8 mm, and Super 8. Although both standard 8 mm and ...
, but are now widely used for display lighting and in the home. More recently, wider beam versions have become available, designed for direct use on supply voltages of 120 or .


Effect of voltage on performance

.Tungsten halogen lamps behave similarly to other incandescent lamps when run on a different voltage. However, the light output is reported as proportional toV^3, and the luminous efficacy is proportional toV^. The normal relationship regarding the lifetime is that it is proportional toV^. For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the luminous efficacy would be about 6.5% higher, but would be expected to have only half the rated life. Halogen lamps are manufactured with enough halogen to match the rate of tungsten evaporation at their design voltage. Increasing the applied voltage increases the rate of evaporation, so at some point, there may be insufficient halogen, and the lamp goes black. Over-voltage operation is not generally recommended. With a reduced voltage, the evaporation is lower, and there may be too much halogen, which can lead to abnormal failure. At much lower voltages, the bulb temperature may be too low to support the halogen cycle, but by this time, the evaporation rate is too low for the bulb to blacken significantly. If the bulbs do blacken, it is recommended to run the lamps at the rated voltage to restart the cycle. (Also available as
PDF
from lutron.com)
There are many situations where halogen lamps are dimmed successfully. However, lamp life may not be extended as much as predicted. The life span of dimming depends on lamp construction, the halogen additive used, and whether dimming is normally expected for this type.


Spectrum

Like all
incandescent light bulb An incandescent light bulb, also known as an incandescent lamp or incandescent light globe, is an electric light that produces illumination by Joule heating a #Filament, filament until it incandescence, glows. The filament is enclosed in a ...
s, a halogen lamp produces a continuous spectrum of light, from near ultraviolet to deep into the infrared. Since the lamp filament can operate at a higher temperature than a non-halogen lamp, the spectrum is shifted toward blue, producing light with a higher effective color temperature and higher power efficiency. High-temperature filaments emit some energy in the UV region. Small amounts of other elements can be mixed into the quartz, so that the ''doped'' quartz (or selective optical coating) blocks harmful UV radiation. Hard glass blocks UV and has been used extensively for the bulbs of car headlights. Alternatively, the halogen lamp can be mounted inside an outer bulb, similar to an ordinary incandescent lamp, which also reduces the risks from the high bulb temperature. Undoped quartz halogen lamps are used in some scientific, medical, and dental instruments as a UV-B source.


Safety

Halogen lamps must run at much higher temperatures than regular incandescent lamps for proper operation. Their small size helps to concentrate the heat on a smaller envelope surface, closer to the filament than a non-halogen incandescent. Because of the very high temperatures, halogen lamps can pose fire and burn hazards. In Australia, numerous house fires each year are attributed to ceiling-mounted halogen downlights. The Western Australia Department of Fire and Emergency Services recommends that homeowners consider instead using cooler-running
compact fluorescent lamp A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incan ...
s or light-emitting diode lamps. Halogen Torchère floor lamps have been banned in some places, such as dormitories, because of the large number of fires they have caused. They were held responsible by the US Consumer Product Safety Commission for 100 fires and 10 deaths between 1992 and 1997. Halogen bulbs operate at high
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
s , and the tall height of the lamps can bring them near
flammable A combustible material is a material that can burn (i.e., sustain a flame) in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort ...
materials, such as
curtain A curtain is a piece of cloth or other material intended to block or obscure light, air drafts, or (in the case of a shower curtain) water. Curtains are often hung on the inside of a building's windows to block the passage of light. For instan ...
s. Some safety codes require halogen bulbs to be protected by a grid or grille, especially for high-power (1–2 kW) bulbs used in
theatre Theatre or theater is a collaborative form of performing art that uses live performers, usually actors to present experiences of a real or imagined event before a live audience in a specific place, often a Stage (theatre), stage. The performe ...
, or by the glass and metal housing of the fixture, to prevent ignition of draperies or flammable objects in contact with the lamp. To reduce unintentional
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
(UV) exposure and to contain hot bulb fragments in the event of explosive bulb failure, general-purpose lamps usually have a UV-absorbing glass filter over or around the bulb. Alternatively, lamp bulbs may be doped or coated to filter out the UV radiation. With adequate filtering, a halogen lamp exposes users to less UV than a standard incandescent lamp producing the same effective level of illumination without filtering. Any surface contamination, notably the oil from human fingertips, can damage the quartz envelope when it is heated. Contaminants, because they absorb more light and heat than the glass does, will create a hot spot on the bulb surface when the lamp is turned on. This extreme, localized heat causes the quartz to change from its vitreous form into a weaker,
crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...
form that leaks gas. This weakening may also cause the bulb to form a bubble, weakening it and leading to its explosion. The small glass envelope may be enclosed in a much larger outer glass bulb, which provides several advantages if a small size is not required: * The outer jacket will be at a much lower, safer temperature, protecting objects or people that might touch it. * The hot-running inner envelope is protected from contamination, and the bulb may be handled without damaging it. * Surroundings are protected from the possible shattering of the inner capsule. * The jacket may filter out UV radiation. * When a halogen bulb is used to replace a normal incandescent bulb in a fitting, the larger jacket makes it mechanically similar to the bulb it replaces * The inner and outer envelopes can be at different pressures, reducing heat dissipation by conduction or convection to optimize the trade-off between luminous efficacy and lifetime.


Form factors

.Halogen lamps are available in a series of different shapes and sizes, and are designated according to a coding system that specifies the diameter of the bulb as well as whether or not the bulb has a built-in infrared-transparent dichroic reflector. Many such lamps have designations that begin with the letter "T" to indicate that they are "tubular", followed by a number indicating the diameter of the tube in eighths of an inch: a T3 bulb, then is a tubular halogen bulb that is in diameter.However, a T-3, T ''hyphen'' 3, is a halogen "tube" lamp that is 3/8 of an inch in diameter with a single bi-pin base rather than a T3 ''cylindrical'' tube 3/8 of an inch in diameter with electrodes at ''opposite ends.'' The designation ''MR'' means " Multifaceted Reflector", with the number following this still corresponding to eighths of an inch in diameter of the overall bulb.Thus, an MR11 is a multifaceted reflector bulb that is 11/8 or 1 3/8 inches in diameter If a lamp has a "G" code,"G" stands for "glass" this will mean the lamp is a bipin shape and the number following the G will indicate the distance in millimeters between the pins, usually either 4, 6.35 or 10; if the G is followed by a letter "Y", then the lamp's pins are thicker than normal— thus, a G6.35 has pins that are 1 mm in diameter but a GY6.35 has pins that are 1.3 mm in diameter. If there is a "C" code, this represents the number of coils in the filament. The length (sometimes also referred to as "height") of any two-ended cylindrical bulb must be specified separately from its form factor code, usually in millimeters, as must the lamp's voltage and wattage— hence, T3 120 V 150 W 118 mm means a double-ended tube-shaped bulb with a diameter of that operates at 120 V and is 150 W and that is also 118 mm long. An R7S is a double-ended, Recessed Single Contact (RSC) linear halogen lamp, usually measuring a length of either 118 mm or 78 mm. Some less common lengths are 189 mm, 254 mm and 331 mm. These lamps have a T3 shape on an RSC/R7S base. These can also be known as J-type and T-type lamps.


Applications

Halogen
headlamp A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term for t ...
s are used in many automobiles. Halogen
floodlights A floodlight is a broad-beamed, gas discharge lamp#High-intensity discharge lamps, high-intensity artificial light. It can provide functional area lighting for travel-ways, parking, entrances, work areas, and sporting venues to enable visibil ...
for outdoor lighting systems, as well as for watercraft, are also manufactured for commercial and recreational use. They are now also used in desktop lamps. Tungsten-halogen lamps are frequently used as a near-infrared light source in
Infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...
. Halogen lamps were used on the Times Square Ball from 1999 to 2006. However, from 2007 onward, the halogen lamps were replaced with LEDs, due to the much longer lifespan, about ten times longer for LEDs over incandescent. The 'New Year' numerals that light up when the Times Square Ball reaches the base used halogen lighting for the last time for the 2009 ball drop.


Heating

Halogen lamps are the heating elements in halogen ovens, infrared heaters and ceramic
cooktop A cooktop (American English), stovetop (Canadian and American English) or hob (British English), is a device commonly used for cooking that is commonly found in kitchens and used to apply heat to the base of cookware, pans or pots. Cooktops are o ...
s. Low-wattage halogen lamp arrays are widely used by monitor lizard keepers. Two or three small halogen lamps can produce all the heat needed in an enclosure and are recognized by the animals as sources of heat, preventing curious individuals from attempting to touch them. Halogen lamps' thick glass lenses are safe to use inside high-humidity reptile enclosures. Banks of powerful tubular halogen lamps were used to simulate the heat of
re-entry Atmospheric entry (sometimes listed as Vimpact or Ventry) is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. Atmospheric entry may be ''uncontrolled entry ...
of space vehicles.Raymond Kane, Heinz Sell, ''Revolution in Lamps: A Chronicle of 50 Years of Progress, Second Edition'', 2001 The Fairmount Press, pp. 72-74


General lighting

Fixed-mount lamps are used in indoor and outdoor flood lighting, although improvements in LED systems are displacing halogen lamps. Round spotlights with built-in multifaceted reflector lamps are widely used in residential and commercial lighting. Tubular halogen lamps provide a large quantity of light from a small source and so can be used to produce powerful flood lamps for architectural lighting effects, or for lighting large areas outdoors. Low-voltage lamps use the GU5.3 and similar bi-pin bases, whereas mains voltage lamps use the same caps as normal mains tungsten filament lamps, or a special GU10/GZ10 base. The GU10/GZ10 bases are shaped to prevent dichroic reflector lamps from being used in luminaires intended for aluminised reflector lamps, which could cause overheating of the fitting. Higher efficiency LED versions of all of these lamps are now available. Tubular lamps with electrical contacts at both ends are now commonly used in standalone lighting and household fixtures. These come in various lengths and power ratings (50–300 W). More powerful lamps are used as portable work lights, with bulbs rated 250 or 500 watts.


Stage lighting

Tungsten halogen lamps are used in the majority of theatrical and studio (film and television) fixtures, including
Ellipsoidal reflector spotlight Ellipsoidal reflector spot (abbreviated to ERS, or colloquially ellipsoidal or ellipse) is the name for a type of stage lighting instrument, named for the ellipsoidal reflector used to collect and direct the light through a barrel that conta ...
s, Source Four, and Fresnels. PAR Cans are also predominantly tungsten halogen.


Specialized

Projection Projection or projections may refer to: Physics * Projection (physics), the action/process of light, heat, or sound reflecting from a surface to another in a different direction * The display of images by a projector Optics, graphics, and carto ...
lamps are used in motion-picture and
slide projector A slide projector is an optical device for projecting enlarged images of photographic slides onto a screen. Many projectors have mechanical arrangements to show a series of slides loaded into a special tray sequentially. 35 mm slide p ...
s for homes and small offices or school use. The compact size of the halogen lamp permits a reasonable size for portable projectors, although heat-absorbing filters must be placed between the lamp and the film to prevent melting. Halogen lamps are sometimes used for inspection lights and microscope stage illuminators. Halogen lamps were used for early flat-screen LCD
backlight A backlight is a form of illumination used in liquid-crystal displays (LCDs) that provides light from the back or side of a display panel. LCDs do not produce light on their own, so they require illumination—either from available light, ambie ...
ing, but other types of lamps, such as CCFL and now LED, are used. Halogen lamps are used as the heating element in the fuser of many types of laser printers. The long tubular lamp heats the fuser roller from the inside, and the heat melts the toner onto the paper.


Disposal

Halogen lamps do not contain any mercury.
General Electric General Electric Company (GE) was an American Multinational corporation, multinational Conglomerate (company), conglomerate founded in 1892, incorporated in the New York (state), state of New York and headquartered in Boston. Over the year ...
says that its quartz halogen lamps would not be classified as hazardous waste.


See also

* Bi-pin connector for base designations GY6.35, G8, etc. * FEL lamp *
Lightbulb socket A lightbulb socket, lightbulb holder, light socket, lamp socket or lamp holder is a device which mechanically supports and provides electrical connections for a compatible electric Lamp (electrical component), lamp base. Sockets allow lamps to ...
for other bases *
List of light sources This is a list of sources of light, the visible part of the electromagnetic spectrum. Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic ener ...


Notes


References


External links

* {{DEFAULTSORT:Halogen Lamp Types of lamp Incandescent light bulbs de:Glühlampe#Sonderformen