Continuous glow lamps are produced for special applications where the electrodes may be cut in the shape of alphanumeric characters and figural shapes.
Lamps are divided into families based on the pressure of gas in the bulb, below. A second distinction used is whether the cathode is heated. Hot cathode lamps have electrodes that operate at a high temperature and are heated by the arc current in the lamp. The heat knocks electrons out of the electrodes by thermionic emission, which helps maintain the arc. In many types the electrodes consist of electrical filaments made of fine wire, which are heated by a separate current at startup, to get the arc started. Cold cathode lamps have electrodes that operate at room temperature. To start conduction in the lamp a high enough voltage (the striking voltage) must be applied to ionize the gas, so these lamps require higher voltage to start.
Another phenomenon associated with HID lamp wear and aging is discoloration of the emitted light beam (“fading”). Commonly, a shift towards blue and/or violet can be observed. This shift is slight at first and is more generally a sign of the lamps being “broken in” whilst still being in good overall working order, but towards the end of its life, the HID lamp is often perceived as only producing blue and violet light. Based on Planck’s law, this is a direct result of the increased voltage and higher temperature necessary to maintain the arc.
The introduction of the metal vapor lamp, including various metals within the discharge tube, was a later advance. The heat of the gas discharge vaporized some of the metal and the discharge is then produced almost exclusively by the metal vapor. The usual metals are sodium and mercury owing to their visible spectrum emission.
High-pressure lamps have a discharge that takes place in gas under slightly less to greater than atmospheric pressure. For example, a high pressure sodium lamp has an arc tube under 100 to 200 torr pressure, about 14% to 28% of atmospheric pressure; some automotive HID headlamps have up to 50 bar or fifty times atmospheric pressure.
Krypton-85 is a gas and is found mixed in with the argon, which is in the arc tube of the lamp. The thorium, which is a solid, is used in the electrodes.
At the end of life, many types of high-intensity discharge lamps exhibit a phenomenon known as cycling. These lamps can be started at a relatively low voltage. As they heat up during operation, however, the internal gas pressure within the arc tube rises and a higher voltage is required to maintain the arc discharge. As a lamp gets older, the voltage necessary to maintain the arc eventually rises to exceed the voltage provided by the electrical ballast. As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, repeatedly.
HID lamps have made indoor gardening practical, particularly for plants that require high levels of direct sunlight in their natural habitat; HID lamps, specifically metal-halide and high-pressure sodium, are a common light source for indoor gardens. They are also used to reproduce tropical intensity sunlight for indoor aquaria.
High pressure sodium lamps, producing up to 150 lumens per watt produce a broader light spectrum than the low pressure sodium lamps. Also used for street lighting, and for artificial photoassimilation for growing plants
References Further reading Waymouth, John (1971). Electric Discharge Lamps. Cambridge, MA: The M.I.T. Press. ISBN 0-262-23048-8. National Highway Traffic Safety Administration. “Glare from headlamps and other front mounted lamps”.
Federal Motor Vehicle Safety Standard No. 108. US Department of Transportation. Retrieved 2006-01-23. External links Wikimedia Commons has media related to Gas discharge lamps. Lamps and Indicators at Curlie (based on DMOZ)
1 Construction 2 Radioactive substances 3 Applications 4 End of life 5 References
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A flicker light bulb, flicker flame light bulb or flicker glow lamp is a gas-discharge lamp which produces light by ionizing a gas, usually neon mixed with helium and a small amount of nitrogen gas, by an electric current passing through two flame shaped electrode screens coated with partially decomposed barium azide. The ionized gas moves randomly between the two electrodes which produces a flickering effect, often marketed as suggestive of a candle flame (see image).
Replacements for the toxic mercury in the HID lamps have been investigated and are a matter of ongoing research. Experiments show promising results and widespread future applications are expected.
Factors of wear come mostly from on/off cycles versus the total on time. The highest wear occurs when the HID burner is ignited while still hot and before the metallic salts have recrystallized.
Metal-halide and ceramic metal-halide lamps can be made to give off neutral white light useful for applications where normal color appearance is critical, such as TV and movie production, indoor or nighttime sports games, automotive headlamps, and aquarium lighting.
Like fluorescent lamps, HID lamps require a ballast to start and maintain their arcs. The method used to initially strike the arc varies: mercury-vapor lamps and some metal-halide lamps are usually started using a third electrode near one of the main electrodes, while other lamp styles are usually started using pulses of high voltage.
Mercury-vapor lamps were the first commercially available HID lamps. Originally they produced a bluish-green light, but more recent versions can produce light with a less pronounced color tint. However, mercury-vapor lamps are falling out of favor and being replaced by sodium-vapor and metal-halide lamps.
Fluorescent lamps, a heated-cathode lamp, the most common lamp in office lighting and many other applications, produces up to 100 lumens per watt
High pressure mercury-vapor lamps are the oldest high pressure lamp type and have been replaced in most applications by metal halide and the high pressure sodium lamps. They require a shorter arc length.
HID lamps are also used in lamps for underwater diving. The higher efficacy of HID lamps compared to halogen units means longer burn times for a given battery size and light output.
A small discharge lamp containing a bi-metallic switch is used to start a fluorescent lamp. In this case the heat of the discharge is used to actuate the switch; the starter is contained in an opaque enclosure and the small light output is not used.
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Mercury-vapor lamps Metal-halide (MH) lamps Ceramic MH lamps Sodium-vapor lamps Xenon short-arc lamps
The history of gas-discharge lamps began in 1675 when French astronomer Jean-Felix Picard observed that the empty space in his mercury barometer glowed as the mercury jiggled while he was carrying the barometer. Investigators, including Francis Hauksbee, tried to determine the cause of the phenomenon. Hauksbee first demonstrated a gas-discharge lamp in 1705. He showed that an evacuated or partially evacuated glass globe, in which he placed a small amount of mercury, while charged by static electricity could produce a light bright enough to read by. The phenomenon of electric arc was first described by Vasily V. Petrov in 1802; Sir Humphry Davy demonstrated in the same year the electric arc at the Royal Institution of Great Britain. Since then, discharge light sources have been researched because they create light from electricity considerably more efficiently than incandescent light bulbs.
The Xenon flash lamp produces a single flash of light in the millisecond-microsecond range and is commonly used in film, photography and theatrical lighting. Particularly robust versions of this lamp, known as strobe lights, can produce long sequences of flashes, allowing for the stroboscopic examination of motion. This has found use in the study of mechanical motion, in medicine and in the lighting of dance halls.
Low-pressure sodium-vapor lamps are extremely efficient. They produce a deep yellow-orange light and have an effective CRI of nearly zero; items viewed under their light appear monochromatic. This makes them particularly effective as photographic safelights. High-pressure sodium lamps tend to produce a much whiter light, but still with a characteristic orange-pink cast. New color-corrected versions producing a whiter light are now available, but some efficiency is sacrificed for the improved color.
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Most HID lamps produce significant UV radiation and require UV-blocking filters to prevent UV-induced degradation of lamp fixture components and fading of dyed items illuminated by the lamp. Exposure to HID lamps operating with faulty or absent UV-blocking filters causes injury to humans and animals, such as sunburn and arc eye. Many HID lamps are designed to quickly extinguish if their outer UV-shielding glass envelope is broken.
HID lamps are typically used when high levels of light and energy efficiency are desired.
Various types of chemistry are used in the arc tubes of HID lamps, depending on the desired characteristics of light intensity, correlated color temperature, color rendering index (CRI), energy efficiency, and lifespan. Varieties of HID lamp include:
Metal halide lamps produce almost white light, and attain 100 lumen per watt light output. Applications include indoor lighting of high buildings, parking lots, shops, sport terrains.
Beginning in the early 1990s, HID lamps have seen applications in automotive headlamps. Xenon, or high-intensity discharge (HID), lighting provides brighter headlights and increases visibility of many peripheral objects (e.g. street signs and pedestrians) left in the shadows by standard halogen lighting.
Many modern vehicles use HID bulbs for the main lighting systems, some applications are now moving from HID bulbs to LED and laser technology. However, this HID technology is not new and was first demonstrated by Francis Hauksbee in 1705.
Brand new high-intensity discharge lamps make more visible light per unit of electric power consumed than fluorescent and incandescent lamps, since a greater proportion of their radiation is visible light in contrast to infrared. However, the lumen output of HID lighting can deteriorate by up to 70% over 10,000 burning hours.
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1 History 2 Color 3 Types 3.1 Low pressure discharge lamps 3.2 High pressure discharge lamps 3.3 High-intensity discharge lamps 4 Other examples 5 See also 6 References 7 Further reading 8 External links
Neon lighting, a widely used form of cold-cathode specialty lighting consisting of long tubes filled with various gases at low pressure excited by high voltages, used as advertising in neon signs.
More sophisticated ballast designs detect cycling and give up attempting to start the lamp after a few cycles. If power is removed and reapplied, the ballast will make a new series of startup attempts.
Low pressure sodium lamps, the most efficient gas-discharge lamp type, producing up to 200 lumens per watt, but at the expense of very poor color rendering. The almost monochromatic yellow light is only acceptable for street lighting and similar applications.
HID lamps have also become common on many aircraft as replacements for traditional landing and taxi lights.
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These isotopes produce ionizing radiation of alpha and beta type. This radiation causes high ionization inside the lamp without being able to escape from the lamp. High ionisation makes arc starting via Townsend avalanche much easier. Moreover, the presence of thorium in electrodes reduces the work function which again results in easier arc starting and sustaining.
Compared to incandescent lamps, gas-discharge lamps offer higher efficiency, but are more complicated to manufacture and most exhibit negative resistance, causing the resistance in the plasma to decrease as the current flow increases. Therefore, they usually require auxiliary electronic equipment such as ballasts to control current flow through the gas, preventing current runaway (arc flash). Some gas-discharge lamps also have a perceivable start-up time to achieve their full light output. Still, due to their greater efficiency, gas-discharge lamps are replacing incandescent lights in many lighting applications.
One hundred years of research later led to lamps without electrodes which are instead energized by microwave or radio frequency sources. In addition, light sources of much lower output have been created, extending the applications of discharge lighting to home or indoor use.
A high-intensity discharge (HID) lamp is a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. Compared to other lamp types, relatively high arc power exists for the arc length. Examples of HID lamps include mercury-vapor lamps, metal halide lamps, ceramic discharge metal halide lamps, sodium vapor lamps and xenon arc lamps
Germicidal lamps are simple low-pressure mercury vapor discharges in a fused quartz envelope.
In combination with phosphors used to generate many colors of light. Widely used in mercury-vapor lamps. Sodium vapor (low pressure) Bright orange-yellow Widely used in sodium vapor lamps. Types
High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with noble gas and often also contains suitable metal or metal salts. The noble gas enables the arc’s initial strike. Once the arc is started, it heats and evaporates the metallic admixture. Its presence in the arc plasma greatly increases the intensity of visible light produced by the arc for a given power input, as the metals have many emission spectral lines in the visible part of the spectrum. High-intensity discharge lamps are a type of arc lamp.
HID lamps are used in high-performance bicycle headlamps, as well as flashlights and other portable lights, because they produce a great amount of light per unit of power. As the HID lights use less than half the power of an equivalent tungsten-halogen light, a significantly smaller and lighter-weight power supply can be used.
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Gas Color Spectrum Notes Image Helium White to orange; under some conditions may be gray, blue, or green-blue. Used by artists for special purpose lighting. Neon Red-orange Intense light. Used frequently in neon signs and neon lamps.
Argon Violet to pale lavender blue Often used together with mercury vapor. Krypton Gray off-white to green. At high peak currents, bright blue-white. Used by artists for special purpose lighting. Xenon Gray or blue-gray dim white.
At high peak currents, very bright green-blue. Used in flashtubes, xenon HID headlamps, and xenon arc lamps. Nitrogen Similar to argon but duller, more pink; at high peak currents bright blue-white. Oxygen Violet to lavender, dimmer than argon Hydrogen Lavender at low currents, pink to magenta over 10 mA Water vapor Similar to hydrogen, dimmer Carbon dioxide Blue-white to pink, in lower currents brighter than xenon Used in carbon dioxide lasers.
Mercury vapor Light blue, intense ultraviolet
The amount of gamma radiation produced by the isotopes that can escape from the lamp is negligible.
The light-producing element of these lamp types is a well-stabilized arc discharge contained within a refractory envelope arc tube with wall loading in excess of 3 W/cm² (19.4 W/in²).
Low-pressure lamps have working pressure much less than atmospheric pressure. For example, common fluorescent lamps operate at a pressure of about 0.3% of atmospheric pressure.
Electric arc Electric glow discharge Emission spectrum Fluorescent lamp Gas-filled tube Hydrargyrum medium-arc iodide lamp List of light sources Over-illumination
The father of the low-pressure gas discharge tube was German glassblower Heinrich Geissler, who beginning in 1857 constructed colorful artistic cold cathode tubes with different gases in them which glowed with many different colors, called Geissler tubes. It was found that inert gases like the noble gases neon, argon, krypton or xenon, as well as carbon dioxide worked well in tubes. This technology was commercialized by French engineer Georges Claude in 1910 and became neon lighting, used in neon signs.
Sometimes the quartz tube containing mercury can explode in a UHP lamp. When that happens, up to 50 mg of mercury vapor is released into the atmosphere. This quantity of mercury is potentially toxic, but the main hazard from broken lamps is glass cuts, and occasional exposure to broken lamps is not expected to have adverse effects. Philips recommends the use of a mercury vacuum cleaner, ventilation or respiratory protection, eye protection, and protective clothing when dealing with broken lamps. Mercury lamps also require special waste disposal, depending on location.
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 gases. Some include additional substances, like mercury, sodium, and metal halides, which are vaporized during startup to become part of the gas mixture. In operation, some of the electrons are forced to leave the atoms of the gas near the anode by the electric field applied between the two electrodes, leaving these atoms positively ionized. The free electrons thus released flowing onto the anode, while the cations thus formed are accelerated by the electric field and flow towards the cathode. Typically, after traveling a very short distance, the ions collide with neutral gas atoms, which transfer their electrons to the ions. The atoms, having lost an electron during the collisions, ionize and speed toward the cathode while the ions, having gained an electron during the collisions, return to a lower energy state while releasing energy in the form of photons. Light of a characteristic frequency is thus emitted. In this way, electrons are relayed through the gas from the cathode to the anode. The color of the light produced depends on the emission spectra of the atoms making up the gas, as well as the pressure of the gas, current density, and other variables. Gas discharge lamps can produce a wide range of colors. Some lamps produce ultraviolet radiation which is converted to visible light by a fluorescent coating on the inside of the lamp’s glass surface. The fluorescent lamp is perhaps the best known gas-discharge lamp.
HID lamps are typically used when high levels of light over large areas are required, and when energy efficiency and/or light intensity are desired. These areas include gymnasiums, large public areas, warehouses, movie theaters, football stadiums, outdoor activity areas, roadways, parking lots, and pathways. More recently, HID lamps have been used in small retail and even residential environments because of advances in reduced lumen bulbs. Ultra-high performance (UHP) HID lamps are used in LCD or DLP projection TV sets or projection displays as well.
Each gas, depending on its atomic structure emits certain wavelengths, its emission spectrum, which determines the color of the light from the lamp. As a way of evaluating the ability of a light source to reproduce the colors of various objects being lit by the source, the International Commission on Illumination (CIE) introduced the color rendering index (CRI). Some gas-discharge lamps have a relatively low CRI, which means colors they illuminate appear substantially different from how they do under sunlight or other high-CRI illumination.
Some HID lamps make use of radioactive substances such as krypton-85 and thorium. These isotopes help start the lamps and improve lamp operating characteristics.