Xenon arc lamp

A xenon arc lamp is a highly specialized type of gas discharge lamp, an electric light that produces light by passing electricity through ionized xenon gas at high pressure. It produces a bright white light that closely mimics natural sunlight, which extends its applications into the film, and daylight simulation industries. Xenon arc lamps are used in movie projectors in theaters, in searchlights, and for, as mentioned previously, specialized uses in industry and research to simulate sunlight, often for product testing.

Xenon headlamps in automobiles are actually metal-halide lamps, where a xenon arc is only used during start-up to correct the color temperature.

Xenon short arc 1
15 kW xenon short-arc lamp used in IMAX projectors
High-speed, slow-motion video of a xenon flashtube. Camera was recording at 44,025 frames per second.

Types

Xenon arc lamps can be roughly divided into three categories: continuous-output xenon short-arc lamps, continuous-output xenon long-arc lamps, and xenon flash lamps (which are usually considered separately).

Each consists of a fused quartz or other heat resistant glass arc tube, with a tungsten metal electrode at each end. The glass tube is first evacuated and then re-filled with xenon gas. For xenon flashtubes, a third "trigger" electrode usually surrounds the exterior of the arc tube. The lifetime of a xenon arc lamp varies according to its design and power consumption, with a major manufacturer quoting average lifetimes ranging from 500 hours (7kW) to 1,500 (1kW).[1]

History and modern usage

100hgxe
An Osram 100 W xenon/mercury short-arc lamp in reflector

Interest in the xenon discharge was first aroused by P. Schulz in 1944, following his discovery of its near-continuous spectrum and high colour rendering white light.[2] Owing to wartime limitations on the availability of this noble gas, significant progress was not made until John Aldington of the British Siemens lamp company published his research in 1949.[3] This triggered intensive efforts at the German Osram company to further develop the technology as a replacement for carbon arcs in cinema projection. The first successful public projection using xenon light was performed on 30 October 1950, when excerpts from a colour film (Das Schwarzwaldmädel) were shown during the 216th session of the German Cinematographic Society in Berlin.[4] The technology was commercially introduced by German Osram in 1952.[5] First produced in the 2 kW size (XBO2001), these lamps saw wide use in movie projection, where they replaced the older, more labor-intensive (to operate) carbon arc lamps.

The white continuous light generated by the xenon arc is spectrally similar to daylight, but the lamp has a rather low efficacy in terms of lumens of visible light output per watt of input power. Today, almost all movie projectors in theaters employ these lamps, with power ratings ranging from 900 watts up to 12 kW. Omnimax (Imax Dome) projection systems use single xenon lamps with ratings as high as 15 kW. As of 2016, laser illumination for digital theater projectors is starting to establish a market presence [6] and has been predicted to supersede the xenon arc lamp for this application.[7]

Lamp construction

Xenon short arc 2
An end-view of a 15 kW IMAX lamp showing the liquid-cooling ports

All modern xenon short-arc lamps use a fused quartz envelope with thoriated tungsten electrodes. Fused quartz is the only economically feasible material currently available that can withstand the high pressure (25 atmospheres for an IMAX bulb) and high temperature present in an operating lamp, while still being optically clear. The thorium dopant in the electrodes greatly enhances their electron emission characteristics. Because tungsten and quartz have different coefficients of thermal expansion, the tungsten electrodes are welded to strips of pure molybdenum metal or Invar alloy, which are then melted into the quartz to form the envelope seal.

Because of the very high power levels involved, large lamps are water-cooled. In those used in IMAX projectors, the electrode bodies are made from solid Invar and tipped with thoriated tungsten. An O-ring seals the tube, so that the naked electrodes do not contact the water. In low power applications the electrodes are too cold for efficient electron emission and are not cooled. In high power applications an additional water cooling circuit for each electrode is necessary. To reduce cost, the water circuits are often not separated and the water needs to be deionized to make it electrically non-conductive, which lets the quartz or some laser media dissolve into the water.

HLR-OSRAM-3KW-A
Perspective view of 3 kW lamp showing plastic safety shield used during shipping.

To achieve maximum efficiency, the xenon gas inside short-arc lamps is maintained at an extremely high pressure — up to 30 atmospheres (440 psi / 3040 kPa) — which poses safety concerns. If a lamp is dropped or ruptures while in service, pieces of the lamp envelope can be thrown at high speed. To mitigate this, large xenon short-arc lamps are normally shipped in protective shields, which will contain the envelope fragments should breakage occur. Normally, the shield is removed once the lamp is installed in the lamp housing. When the lamp reaches the end of its useful life, the protective shield is put back on the lamp, and the spent lamp is then removed from the equipment and discarded. As lamps age, the risk of failure increases, so bulbs being replaced are at the greatest risk of explosion. Lamp manufacturers recommend the use of eye protection when handling xenon short-arc lamps. Some lamps, especially those used in IMAX projectors, require the use of full-body protective clothing.

Light generation mechanism

Xenon arc lamp profile
Output profile of a xenon arc lamp.

Xenon short-arc lamps come in two distinct varieties: pure xenon, which contains only xenon gas; and xenon-mercury, which contains xenon gas and a small amount of mercury metal.

Pure xenon

In a pure xenon lamp, the majority of the light is generated within a tiny, pinpoint-sized cloud of plasma situated where the electron stream leaves the face of the cathode. The light generation volume is cone-shaped, and the luminous intensity falls off exponentially moving from cathode to anode. Electrons passing through the plasma cloud strike the anode, causing it to heat. As a result, the anode in a xenon short-arc lamp either has to be much larger than the cathode or be water-cooled, to dissipate the heat. The output of a pure xenon short-arc lamp offers fairly continuous spectral power distribution with a color temperature of about 6200K and color rendering index close to 100.[8] However, even in a high pressure lamp there are some very strong emission lines in the near infrared, roughly in the region from 850–900 nm. This spectral region can contain about 10% of the total emitted light. Light intensity ranges from 20,000 to 500,000 cd/cm2. An example is the "XBO lamp", which is an OSRAM trade name for a pure xenon short-arc lamp.[8]

For some applications such as endoscopy and dental technology light guide systems are included.

Xenon-mercury

In xenon-mercury short-arc lamps, the majority of the light is generated in a pinpoint-sized cloud of plasma situated at the tip of each electrode. The light generation volume is shaped like two intersecting cones, and the luminous intensity falls off exponentially moving towards the centre of the lamp. Xenon-mercury short-arc lamps have a bluish-white spectrum and extremely high UV output. These lamps are used primarily for UV curing applications, sterilizing objects, and generating ozone.

The very small size of the arc makes it possible to focus the light from the lamp with moderate precision. For this reason, xenon arc lamps of smaller sizes, down to 10 watts, are used in optics and in precision illumination for microscopes and other instruments, although in modern times they are being displaced by single mode laser diodes and white light supercontinuum lasers which can produce a truly diffraction-limited spot. Larger lamps are employed in searchlights where narrow beams of light are generated, or in film production lighting where daylight simulation is required.

All xenon short-arc lamps generate substantial ultraviolet radiation. Xenon has strong spectral lines in the UV bands, and these readily pass through the fused quartz lamp envelope. Unlike the borosilicate glass used in standard lamps, fused quartz readily passes UV radiation unless it is specially doped. The UV radiation released by a short-arc lamp can cause a secondary problem of ozone generation. The UV radiation strikes oxygen molecules in the air surrounding the lamp, causing them to ionize. Some of the ionized molecules then recombine as O3, ozone. Equipment that uses short-arc lamps as the light source must contain UV radiation and prevent ozone build-up.

Many lamps have a shortwave UV blocking coating on the envelope and are sold as "ozone free" lamps. These "ozone free" lamps are used commonly in indoor applications, where proper ventilation is not easily accessible. The company WACOM has also a long history of xenon lamp production.[9] Some lamps have envelopes made out of ultra-pure synthetic fused silica (such as "Suprasil"), which roughly doubles the cost, but which allows them to emit useful light into the vacuum UV region. These lamps are normally operated in a pure nitrogen atmosphere.

Ceramic xenon lamps

Cermax2kw
A Cermax 2 kW xenon lamp from a video projector. A pair of heatsinks are clamped on the two metal bands around the perimeter, which also double to supply power to the lamp's electrodes.

Xenon short-arc lamps also are manufactured with a ceramic body and an integral reflector. They are available in many output power ratings with either UV-transmitting or blocking windows. The reflector options are parabolic (for collimated light) or elliptical (for focused light). They are used in a wide variety of applications, such as video projectors, fiber optic illuminators, endoscope and headlamp lighting, dental lighting, and search lights.

Power supply requirements

HLR-SHORT-ARC-SUPPLY-B
A 1 kW xenon short-arc lamp power supply with the cover removed.

Xenon short-arc lamps have a negative temperature coefficient like other gas discharge lamps. They are operated at low-voltage, high-current, DC and started with a high voltage pulse of 20 to 50kV. As an example, a 450 W lamp operates normally at 18 V and 25 A once started. They are also inherently unstable, prone to phenomena such as plasma oscillation and thermal runaway. Because of these characteristics, xenon short-arc lamps require a proper power supply that operates without flickering in the flame, which could ultimately damage the electrodes..

Automotive headlamps

In 1991 "xenon headlamps" were introduced for vehicles (BMW E32). These are actually metal-halide lamps; the xenon gas is used only to provide some light immediately upon lamp startup, as required for safety in an automotive headlamp application. Full intensity is reached 20 to 30 seconds later once the salts of sodium and scandium are vapourised by the heat of the xenon arc. The lamp envelope is small and the arc spans only a few millimetres. An outer hard glass tube blocks the escape of ultraviolet radiation that would tend to damage plastic headlamp components. The first xenon headlamps contained mercury; newer types do not.

Xenon long-arc-lamps

These are structurally similar to short-arc lamps except that the distance between the electrodes in glass tube is greatly elongated. When mounted within an elliptical reflector, these lamps are frequently used to simulate sunlight in brief flashes, often for photography. Typical uses include solar cell testing (with the use of optical filters), solar simulation for age testing of materials, rapid thermal processing, material inspection and sintering.

Though not commonly known outside of Russia and the former Soviet satellite countries, long arc xenon lamps were used for general illumination of large areas such as rail stations, sports arenas, mining operations, and nuclear power plant high bay spaces. These lamps, Лампа ксеноновая ДКСТ, literally "lamp xenon DKST" were characterized by high wattages ranging from 2kW to 100 kW. The lamps operated in a peculiar discharge regime where the plasma was thermalized, that is, the electrons were not significantly hotter than the gas itself. Under these conditions a positive current-voltage curve was demonstrated. This allowed the larger common sizes such as 5 and 10kW to operate directly from mains AC at 110 and 220 volts respectively without a ballast - only a series igniter was necessary to start the arc. The lamps produced around 30 lumens/watt, which is about double the efficiency of the tungsten incandescent lamp, but less than more modern sources such as metal halide. They had the advantage of no mercury content, convective air cooling, no high pressure rupture risk, and nearly perfect color rendition. Due to low efficiency and competition from more common lamp types, few installations remain today, but where they do, they can be recognized by a characteristic rectangular/elliptical reflector, and crisp blue-white light from a relatively long tubular source.

See also

References

  1. ^ "Ushio - product data page".
  2. ^ Edelgasbögen, P.Schulz, Reichsbericht f.Physik, Vol.1 (1944) p147
  3. ^ Gas Arcs, J.N. Aldington, Transactions of the Illuminating Engineering Society of London, Vol.14 (1949) pp19-51.
  4. ^ Die Neuen Xenon-Hochdrucklampen, K. Ittig, K. Larché, F. Michalk, Technisch-wissenschaftliche Abhandlungen der Osram-Gesellchaft, Vol.6 (1953) pp33-38.
  5. ^ Technik der Spezial-Entladungslampen, publ. Osram GmbH 1989, p24.
  6. ^ "Christie announces installation of laser projectors".
  7. ^ "Example of article discussing laser illumination replacing the xenon arc".
  8. ^ a b "OSRAM SYVLANIA XBO" (PDF). Archived from the original (PDF) on 2013-07-18.
  9. ^ "WACOM KXL" (PDF).
Arc lamp

An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, was the first practical electric light. It was widely used starting in the 1870s for street and large building lighting until it was superseded by the incandescent light in the early 20th century. It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II. The carbon arc lamp is now obsolete for most of these purposes, but it is still used as a source of high intensity ultraviolet light.

The term is now used for gas discharge lamps, which produce light by an arc between metal electrodes through an inert gas in a glass bulb. The common fluorescent lamp is a low-pressure mercury arc lamp. The xenon arc lamp, which produces a high intensity white light, is now used in many of the applications which formerly used the carbon arc, such as movie projectors and searchlights.

Artificial sunlight

Artificial sunlight is the use of a light source to simulate sunlight where the unique characteristics of sunlight are needed, but where sufficient natural sunlight is not available or is not feasible. A light source used to simulate sunlight is a solar simulator.

Electric light

An electric light is a device that produces visible light from electric current. It is the most common form of artificial lighting and is essential to modern society, providing interior lighting for buildings and exterior light for evening and nighttime activities. In technical usage, a replaceable component that produces light from electricity is called a lamp. Lamps are commonly called light bulbs; for example, the incandescent light bulb. Lamps usually have a base made of ceramic, metal, glass or plastic, which secures the lamp in the socket of a light fixture. The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap.

The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor.

Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. Cornish chemist Humphry Davy developed the first incandescent light in 1802, followed by the first practical electric arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. The development of a steadily glowing filament suitable for interior lighting took longer, but by the early twentieth century inventors had successfully developed options, replacing the arc light with incandescents.The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to many applications. Most modern electric lighting is powered by centrally generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems. Battery-powered light is often reserved for when and where stationary lights fail, often in the form of flashlights, electric lanterns, and in vehicles.

Fluorescence microscope

A fluorescence microscope is an optical microscope that uses fluorescence and phosphorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study properties of organic or inorganic substances. The "fluorescence microscope" refers to any microscope that uses fluorescence to generate an image, whether it is a more simple set up like an epifluorescence microscope, or a more complicated design such as a confocal microscope, which uses optical sectioning to get better resolution of the fluorescent image.On 8 October 2014, the Nobel Prize in Chemistry was awarded to Eric Betzig, William Moerner, and Stefan Hell for "the development of super-resolved fluorescence microscopy," which brings "optical microscopy into the nanodimension".

Fluorometer

A fluorometer or fluorimeter is a device used to measure parameters of fluorescence: its intensity and wavelength distribution of emission spectrum after excitation by a certain spectrum of light. These parameters are used to identify the presence and the amount of specific molecules in a medium. Modern fluorometers are capable of detecting fluorescent molecule concentrations as low as 1 part per trillion.

Fluorescence analysis can be orders of magnitude more sensitive than other techniques. Applications include chemistry/biochemistry, medicine, environmental monitoring. For instance, they are used to measure chlorophyll fluorescence to investigate plant physiology.

Heligoland lighthouse

Heligoland lighthouse (German: Leuchtturm Helgoland) is located on Germany's only offshore island, Heligoland. Constructed during World War II as an anti-aircraft tower, it was turned into a lighthouse in 1952. It features the strongest light on the German North Sea coast with a range of 28 nautical miles (52 km) so that it can be seen as far as on the East Frisian or the North Frisian islands and Halligen. The lighthouse is operated by the Tönning water and shipping authority.

Light fixture

A light fixture (US English), light fitting (UK English), or luminaire is an electrical device that contains an electric lamp that provides illumination. All light fixtures have a fixture body and one or more lamps. The lamps may be in sockets for easy replacement—or, in the case of some LED fixtures, hard-wired in place.

Fixtures may also have a switch to control the light, either attached to the lamp body or attached to the power cable. Permanent light fixtures, such as dining room chandeliers, may have no switch on the fixture itself, but rely on a wall switch.

Fixtures require an electrical connection to a power source, typically AC mains power, but some run on battery power for camping or emergency lights. Permanent lighting fixtures are directly wired. Movable lamps have a plug and cord that plugs into a wall socket.

Light fixtures may also have other features, such as reflectors for directing the light, an aperture (with or without a lens), an outer shell or housing for lamp alignment and protection, an electrical ballast or power supply, and a shade to diffuse the light or direct it towards a workspace (e.g., a desk lamp). A wide variety of special light fixtures are created for use in the automotive lighting industry, aerospace, marine and medicine sectors.

Portable light fixtures are often called lamps, as in table lamp or desk lamp. In technical terminology, the lamp is the light source, which, in casual terminology, is called the light bulb. The International Electrotechnical Commission (IEC) recommends the term luminaire for technical use.

Lightfastness

Lightfastness is a property of a colourant such as dye or pigment that describes how resistant to fading it is when exposed to light. Dyes and pigments are used for example for dyeing of fabrics, plastics or other materials and manufacturing paints or printing inks.

The bleaching of the color is caused by the impact of ultraviolet radiation in the chemical structure of the molecules giving the color of the subject. The part of a molecule responsible for its color is called the chromophore.Light encountering a painted surface can either alter or break the chemical bonds of the pigment, causing the colors to bleach or change in a process known as photodegradation. Materials that resist this effect are said to be lightfast. The electromagnetic spectrum of the sun contains wavelengths from gamma waves to radio waves. The high energy of ultraviolet radiation in particular accelerates the fading of the dye.The photon energy of UVA-radiation which is not absorbed by atmospheric ozone exceeds the dissociation energy of the carbon-carbon single bond, resulting in the cleavage of the bond and fading of the color. Inorganic colourants are considered to be more lightfast than organic colourants. Black colourants are usually considered the most lightfast.Lightfastness is measured by exposing a sample to a lightsource for a predefined period of time and then comparing it to an unexposed sample.

List of light sources

This is a list of sources of light, including both natural and artificial processes that emit light. This article focuses on sources that produce wavelengths from about 390 to 700 nanometers, called visible light.

List of plasma physics articles

This is a list of plasma physics topics.

Luminous efficacy

Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on context, the power can be either the radiant flux of the source's output, or it can be the total power (electric power, chemical energy, or others) consumed by the source.

Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation, and the latter luminous efficacy of a source or overall luminous efficacy.Not all wavelengths of light are equally visible, or equally effective at stimulating human vision, due to the spectral sensitivity of the human eye; radiation in the infrared and ultraviolet parts of the spectrum is useless for illumination. The luminous efficacy of a source is the product of how well it converts energy to electromagnetic radiation, and how well the emitted radiation is detected by the human eye.

Microfadeometry

Microfadeometry is a technique that uses tiny spots of intense light to probe and measure color changes in objects of art that are particularly sensitive to light exposure.

This process is completed using a recently designed instrument known as a microfading tester. The data from the test is represented by a reflectance spectra.

Peripheral vision horizon display

The peripheral vision horizon display, also called PVHD or the Malcolm Horizon (after inventor Dr. Richard Malcolm), is an aircraft cockpit instrument which assists pilots in maintaining proper attitude.

The PVHD was developed in the mid-1970s and manufactured in the early 1980s as a cockpit instrument to assist the pilot with being better aware of the aircraft attitude at all times. The development of the PVHD was driven by a high incidence of military aircraft accidents due to "attitude awareness issues." The PVHD was noted to have a subliminal effect on the pilot because in actual use the display was set so dim that it could barely be seen.

The PVHD was well received by pilots that tested it in helicopters as well as fixed-wing aircraft. It was flown in F-4s and A-10s, as well as helicopters. Initial production in 1983, however, was for the SR-71 Blackbird as an aid when refueling in the air.The initial concept demonstration was done in Canadian military laboratories and later development was undertaken by Varian Canada in Georgetown, Ontario. In 1981, Varian sold the project to Garrett Manufacturing in Rexdale, Toronto, Ontario.

Polilight

The Polilight is a portable, high-intensity, filtered light source used by forensic scientists and others to detect fingerprints, bodily fluids and other evidence from crime scenes and other places.Similar products to the Polilight Hola include the Foster + Freeman Crime-lite, Ultralite ALS and the Optimax Multilite, all of which use light-emitting diodes to produce high-intensity light of varying wavelengths.

Sapphire

Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al2O3) with trace amounts of elements such as iron, titanium, chromium, copper, or magnesium. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. The only color that sapphire cannot be is red – as red colored corundum is called ruby, another corundum variety. Pink colored corundum may be either classified as ruby or sapphire depending on locale.

Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics (especially integrated circuits and GaN-based LEDs).

Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.

Solar simulator

A solar simulator (also artificial sun) is a device that provides illumination approximating natural sunlight. The purpose of the solar simulator is to provide a controllable indoor test facility under laboratory conditions, used for the testing of solar cells, sun screen, plastics, and other materials and devices.

Talaria projector

Talaria was the brand name of a large-venue video projector from General Electric introduced in 1983.

Light from a Xenon arc lamp was modulated by a light valve consisting of a rotating glass disc that was continuously re-coated with a viscous oil. An electron beam similar to the one in a cathode ray tube traced a raster on the surface of the coated glass, deforming the surface of the oil. Where the oil was undisturbed, the light would be reflected into a light trap. The raster traced into the oil formed a diffraction grating.

The basic unit was monochrome (PJ7000 line). Color display is accomplished in one of two ways:

The single lens color projector (PJ5000 line) use dichroic filters to separate the white light of the xenon bulb in two channels, Green and Magenta.

RGB color separation and processing is obtained using vertical wobbulation of the electron beam on the oil film to modulate the green channel and sawtooth modulation is added to the horizontal sweep to separate and modulate Red and Blue channels. The optical system used in the Talaria line is a Schlieren optic like an Eidophor, but the color extraction is much more complex.

Two units (MLV) or three units (3LV) are stacked one atop the other, each one devoted to a single color (3LV).In early models (PJ5000), the light source was a 650 watt xenon bulb (sealed beam) similar to the units in modern 35mm film projectors, and produced 250 lumens at a 75:1 contrast ratio. The later 3LV model produced as much as 3500 lumens at a 250:1 contrast ratio.The later LV series had an optional "Multiple Personality" (MP) module that would allow the projector to display various resolutions and scan rates produced by computers of the time. It could produce an 8,000 lumen image onto a 15 foot by 20 foot screen from 64 feet away.

Xenon lamp

Xenon lamp may refer to:

Xenon arc lamp

Xenon flash lamp

An incandescent light bulb filled with xenon gas to improve life span or efficiency

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