High-intensity discharge lamps (HID lamps) are a type of electricalgas-discharge lamp which produces light by means of an electric arc between tungstenelectrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube.[1] This tube is filled with noble gas and often also contains suitable metal or metal salts.[clarification needed] 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.
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.
Many modern vehicles use HID bulbs for the main lighting systems, although some applications are now moving from HID bulbs to LED and laser technology.[2]
Construction
Diagram of a high-pressure sodium lampA high-pressure sodium lamp, Philips Master SDW-T 100W
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 watts per square centimetre (19W/in2).
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.
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.
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.
Ballasts for discharge lamps
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.
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.[3]
Krypton-85 is a gas and is found mixed in with the argon, which is in the arc tube of the lamp.[8] The thorium, which is a solid, is used in the electrodes.[8]
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.[6] 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.
The amount of gamma radiation produced by the isotopes that can escape from the lamp is negligible.[6]
Applications
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 theatres, football stadiums,[9] 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.
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.
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.
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.
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.
HID lamps have also become common on many aircraft as replacements for traditional landing and taxi lights.[citation needed]
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.
Color Temperatures
HID lamps are available in a variety of colors (commonly referred to as color temperatures) and measured in Kelvins (K). The Kelvin color temperature scale ranges from 1000K (amber) to 3000K (yellow) to 5500K (white) to 8000K (blue) to 12000K (purple).
HID Lamp Color Temperature Range
HID lamps produce different colors of light primarily through the use of various metal additives in the lamp's arc tube and the physics of the gas discharge process.[10]
Metal Additives: HID lamps contain an arc tube filled with a mixture of gases, including a noble gas (like xenon). These metal additives are crucial for producing different colors of light. Different metals emit light at specific wavelengths when energized, and this characteristic determines the lamp's color output.
Gas Discharge Process: The lamp's operation involves creating an electric arc across the electrodes within the arc tube. This arc generates intense heat and excites the gases and metal additives within the tube. As the excited atoms return to their ground state, they release energy in the form of light.
Spectrum Emission: The specific spectrum of light emitted depends on the energy levels of the excited atoms and the properties of the metal additives. Each metal emits light at certain wavelengths, resulting in specific colors
Phosphor Coating: Some HID lamps, like Mercury Vapor lamps, also utilize phosphor coatings on the inner surface of the arc tube. These phosphors absorb the ultraviolet (UV) light emitted by the excited gas atoms and then re-emit visible light. The combination of UV light and the emitted visible light creates a broader spectrum of colors.
Color Rendering Index (CRI): HID lamps are not always known for their excellent color rendering properties. Color rendering refers to how accurately the light source displays the true colors of objects compared to natural sunlight. Different HID lamps have varying CRI values, with some providing better color rendering than others.
HID Headlamp Kelvin Chart
The choice of metal additives and their concentrations enables lamp manufacturers to create HID lamps with distinct color temperatures and spectral characteristics to meet different lighting needs.
The majority of HID lamps are produced in the color temperature range of 5000K to 6000K, which is similar to natural daylight. This is useful for applications requiring high levels of luminosity such as sport stadiums, warehouses, projection TVs, and gardening lights.[11]
However, for certain applications such as automotive headlamps, HID lamps are produced in nearly every color from yellow and white to blue and purple.[12]
End of life
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.
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. 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.
Another phenomenon associated with HID lamp wear and aging is discoloration of the emitted light beam ("fading"[13]). 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.
Sometimes the quartz tube containing mercury can explode in a UHP lamp.[14] When that happens, up to 50mg 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 always require specialised disposal or recycling, which is legally mandatory in many locations depending on jurisdiction.[15]
Related Research Articles
Artificial lighting technology began to be developed tens of thousands of years ago and continues to be refined in the present day.
An arc lamp or arc light is a lamp that produces light by an electric arc.
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than an incandescent lamp. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output. For comparison, the luminous efficacy of an incandescent bulb may only be 16 lumens per watt.
A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered "cold" if it emits more electrons than can be supplied by thermionic emission alone. It is used in gas-discharge lamps, such as neon lamps, discharge tubes, and some types of vacuum tube. The other type of cathode is a hot cathode, which is heated by electric current passing through a filament. A cold cathode does not necessarily operate at a low temperature: it is often heated to its operating temperature by other methods, such as the current passing from the cathode into the gas.
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 triggered, ionizes and conducts a high-voltage pulse to make light. Flashtubes are used most in photography; they also are used in science, medicine, industry, and entertainment.
A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric discharge in gases, and operate by ionizing the gas with an applied voltage sufficient to cause electrical conduction by the underlying phenomena of the Townsend discharge. A gas-discharge lamp is an electric light using a gas-filled tube; these include fluorescent lamps, metal-halide lamps, sodium-vapor lamps, and neon lights. Specialized gas-filled tubes such as krytrons, thyratrons, and ignitrons are used as switching devices in electric devices.
A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.
Hydrargyrum quartz iodide (HQI) is a trademark name of Osram's brand of metal halide lamps made for general floodlighting, arena floodlighting, shop and commercial and industrial lighting. Hydrargyrum is the Latin name for the element mercury. When heated, mercury vapour is created inside the lamp, and deposited when it cools.
A Geissler tube is a precursor to modern gas discharge tubes, demonstrating the principles of electrical glow discharge, akin to contemporary neon lights, and central to the discovery of the electron. This device was developed in 1857 by Heinrich Geissler, a German physicist and glassblower. A Geissler tube is composed of a sealed glass cylinder of various shapes, which is partially evacuated and equipped with a metal electrode at each end. It contains rarefied gases—such as neon or argon, air, mercury vapor, or other conductive substances, and sometimes ionizable minerals or metals like sodium. When a high voltage is applied between the electrodes, there is an electric current through the tube, causing gas molecules to ionize by shedding electrons. The free electrons reunite with the ions and the resulting energic atoms emit light via fluorescence, with the emitted color characteristic of the contained material.
A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger soda lime or borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube.
A metal-halide lamp is an electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides. It is a type of high-intensity discharge (HID) gas discharge lamp. Developed in the 1960s, they are similar to mercury vapor lamps, but contain additional metal halide compounds in the quartz arc tube, which improve the efficiency and color rendition of the light. The most common metal halide compound used is sodium iodide. Once the arc tube reaches its running temperature, the sodium dissociates from the iodine, adding orange and reds to the lamp's spectrum from the sodium D line as the metal ionizes. As a result, metal-halide lamps have high luminous efficacy of around 75–100 lumens per watt, which is about twice that of mercury vapor lights and 3 to 5 times that of incandescent lights and produce an intense white light. Lamp life is 6,000 to 15,000 hours. As one of the most efficient sources of high CRI white light, metal halides as of 2005 were the fastest growing segment of the lighting industry. They are used for wide area overhead lighting of commercial, industrial, and public places, such as parking lots, sports arenas, factories, and retail stores, as well as residential security lighting, automotive headlamps and indoor cannabis grow operations.
The induction lamp, electrodeless lamp, or electrodeless induction lamp is a gas-discharge lamp in which an electric or magnetic field transfers the power required to generate light from outside the lamp envelope to the gas inside. This is in contrast to a typical gas discharge lamp that uses internal electrodes connected to the power supply by conductors that pass through the lamp envelope. Eliminating the internal electrodes provides two advantages:
Hydrargyrum medium-arc iodide (HMI) is the trademark name of Osram's brand of metal-halide gas discharge medium arc-length lamp, made specifically for film and entertainment applications. Hydrargyrum comes from the Greek name for the element mercury.
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 to simulate sunlight, with applications in movie projectors in theaters, in searchlights, 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.
A ceramic metal-halide lamp (CMH), also generically known as a ceramic discharge metal-halide (CDM) lamp, is a type of metal-halide lamp that is 10–20% more efficient than the traditional quartz metal halide and produces a superior color rendition.
Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma.
A grow light is an electric light to help plants grow. Grow lights either attempt to provide a light spectrum similar to that of the sun, or to provide a spectrum that is more tailored to the needs of the plants being cultivated. Outdoor conditions are mimicked with varying colour temperatures and spectral outputs from the grow light, as well as varying the intensity of the lamps. Depending on the type of plant being cultivated, the stage of cultivation, and the photoperiod required by the plants, specific ranges of spectrum, luminous efficacy and color temperature are desirable for use with specific plants and time periods.
Plasma lamps are a type of electrodeless gas-discharge lamp energized by radio frequency (RF) power. They are distinct from the novelty plasma lamps that were popular in the 1980s.
Electric discharge in gases occurs when electric current flows through a gaseous medium due to ionization of the gas. Depending on several factors, the discharge may radiate visible light. The properties of electric discharges in gases are studied in connection with design of lighting sources and in the design of high voltage electrical equipment.
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