A xenon arc lamp is a highly specialized type of
gas discharge lamp
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma.
Typically, such lamps use a
noble gas (argon, neon, krypton, and xenon) or a mixture of these ...
, an
electric light
An electric light, lamp, or light bulb is an electrical component that produces light. It is the most common form of artificial lighting. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the soc ...
that produces light by passing electricity through
ionized
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
xenon
Xenon is a chemical element with the 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 ...
gas at high pressure. It produces a bright white light to simulate
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
, with applications in
movie projector
A movie projector is an optics, opto-mechanics, mechanical device for displaying Film, motion picture film by projecting it onto a movie screen, screen. Most of the optical and mechanical elements, except for the illumination and sound devices ...
s in
theaters
Theatre or theater is a collaborative form of performing art that uses live performers, usually actors or actresses, to present the experience of a real or imagined event before a live audience in a specific place, often a stage. The perform ...
, in
searchlight
A searchlight (or spotlight) is an apparatus that combines an extremely bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular direc ...
s, and for specialized uses in industry and research. For instance, Xenon arc lamps with
mercury lamps are the two most common lamps used in
wide-field fluorescence microscopes.
Types
Xenon
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, ...
s can be roughly divided into three categories: continuous-output xenon short-arc lamps, continuous-output xenon long-arc lamps, and
xenon flash lamp
A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
s (which are usually considered separately).
Each consists of a
fused quartz
Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...
or other heat resistant
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
arc tube, with a
tungsten
Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...
metal
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
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).
History
![D G Xe Osram XBO1001](https://upload.wikimedia.org/wikipedia/commons/d/de/D_G_Xe_Osram_XBO1001.jpg)
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. 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.
This triggered intensive efforts at the German
Osram
Osram Licht AG is a German company that makes electric lights, headquartered in Munich and Premstätten (Austria). Osram positions itself as a high-tech photonics company that is increasingly focusing on sensor technology, visualization and tre ...
company to further develop the technology as a replacement for carbon arcs in cinema projection. The xenon lamp promised tremendous advantages of a more stable arc with less flicker, and its non-consumable electrodes allowed longer films to be shown without interruptions. Osram's primary contribution to this achievement was its thorough research of xenon discharge physics, which directed its developments towards very short arcs for DC operation with a particular electrode and bulb geometry. The cathode is kept small to reach high temperatures for thermionic emission, the anode being larger to dissipate the heat generated as incoming electrons are decelerated. Most light is generated immediately in front of the cathode tip, where arc temperatures reach 10,000°C. The plasma is accelerated towards the anode and stabilised by the electrode shapes plus intrinsic magnetic compression generated by the current flow, and convection effects controlled by the bulb shape.
Following these developments, 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. The technology was commercially introduced by German
Osram
Osram Licht AG is a German company that makes electric lights, headquartered in Munich and Premstätten (Austria). Osram positions itself as a high-tech photonics company that is increasingly focusing on sensor technology, visualization and tre ...
in 1952. First produced in the 2
kW size (XBO2001), and the 1
kW (XBO1001) these lamps saw wide use in
movie projection, where they replaced the older, more labor-intensive (to operate)
carbon 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, ...
s.
Modern usage
The white continuous light generated by the xenon arc is spectrally similar to daylight, but the lamp has a rather low
efficacy
Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as ''effectiveness'', and it has often been used synonymously, although in pharmacology a pragmatic clinical trial#Efficacy versu ...
in terms of
lumens of visible light output per
watt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
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 is a proprietary system of high-resolution cameras, film formats, film projectors, and theaters known for having very large screens with a tall aspect ratio (approximately either 1.43:1 or 1.90:1) and steep stadium seating.
Graeme F ...
(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 and has been predicted to supersede the xenon arc lamp for this application.
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
microscope
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
s 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
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
. Xenon has strong spectral lines in the UV bands, and these readily pass through the fused quartz lamp envelope. Unlike the
borosilicate glass
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), ma ...
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
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
generation. The UV radiation strikes
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
molecules in the air surrounding the lamp, causing them to ionize. Some of the ionized molecules then recombine as O
3, ozone. Equipment that uses short-arc lamps as the light source must contain UV radiation shielding and prevent ozone build-up.
Many lamps have a
shortwave
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 me ...
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. Some lamps have envelopes made out of ultra-pure synthetic
fused silica
Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...
(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.
Lamp construction
All modern xenon short-arc lamps use a fused quartz envelope with
thoriated tungsten
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as ...
electrodes. Fused quartz is the only economically feasible material currently available that can withstand the high pressure (25 atmospheres for an
IMAX
IMAX is a proprietary system of high-resolution cameras, film formats, film projectors, and theaters known for having very large screens with a tall aspect ratio (approximately either 1.43:1 or 1.90:1) and steep stadium seating.
Graeme F ...
bulb) and high temperature present in an operating lamp, while still being optically clear. The
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
dopant in the electrodes greatly enhances their
electron emission
In physics, electron emission is the ejection of an electron from the surface of matter, or, in beta decay (β− decay), where a beta particle (a fast energetic electron or positron) is emitted from an atomic nucleus transforming the original nucl ...
characteristics. Because tungsten and quartz have different
coefficients of thermal expansion, the tungsten electrodes are welded to strips of pure
molybdenum
Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
metal or
Invar
Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel–iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name ''Invar'' comes from the word ''invariable'', referring to its relative lac ...
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
An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more par ...
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.
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](https://upload.wikimedia.org/wikipedia/commons/1/11/Xenon_arc_lamp_profile.png)
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
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
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
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
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
A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in ...
close to 100.
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/cm
2. An example is the "XBO lamp", which is an OSRAM trade name for a pure xenon short-arc lamp.
For some applications such as endoscopy and dental technology light guide systems are included.
Xenon-mercury
![Xenon short-arc bulb](https://upload.wikimedia.org/wikipedia/commons/9/96/Xenon_short-arc_bulb.jpg)
As in a pure xenon lamp, the majority of the light produced radiates from a pinpoint-sized cloud of plasma near the face of the cathode. However, the plasma cloud in a xenon-mercury lamp is often smaller than that of a pure xenon lamp of equivalent size, due to the electron stream losing its energy more rapidly to the heavier mercury atoms. 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
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
.
Ceramic xenon lamps
![2 kW xenon lamba bir vid](https://upload.wikimedia.org/wikipedia/commons/9/90/2_kW_xenon_lamba_bir_vid.jpg)
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
Xenon short-arc lamps have a
negative temperature coefficient
A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property ''R'' that changes when the temperature changes by ''dT'', the temperature coefficient α is def ...
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 Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability i ...
and
thermal runaway
Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way t ...
. 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.
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
Elliptical may mean:
* having the shape of an ellipse, or more broadly, any oval shape
** in botany, having an elliptic leaf shape
** of aircraft wings, having an elliptical planform
* characterised by ellipsis (the omission of words), or by conc ...
reflector, these lamps are frequently used to simulate sunlight in brief flashes, often for photography. Typical uses include
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. 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, russian: Лампа ксеноновая ДКСТ, label=none, 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
*
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 ...
References
{{Artificial light sources
Gas discharge lamps
Xenon
Articles containing video clips