A mercury-vapor lamp is a gas discharge lamp which uses mercury in an excited state to produce light. Gas discharge lamps are a family of artificial light sources that generate light by sending an Electrical discharge through an ionized gas i Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. Fused quartz and fused silica are types of Glass containing primarily Silica in amorphous (non- Crystalline form Borosilicate glass is a type of Glass with the main glass-forming constituents Silica and Boron oxide. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from ultraviolet radiation, and a convenient mounting for the fused quartz arc tube. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays
Mercury vapor lamps (and their relatives) are often used because they are relatively efficient. Luminous efficacy is a property of Light sources which indicates what portion of the emitted Electromagnetic radiation is usable for human vision. Phosphor coated bulbs offer better color rendition than either high- or low-pressure sodium vapor lamps. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons The CIE color rendering index ( CRI) (or colour rendering index in British-style spelling sometimes called color rendition index) is a quantitative A sodium vapor lamp is a Gas discharge lamp which uses Sodium in an excited state to produce Light They also offer a very long lifetime, as well as intense lighting for several applications.
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Theory and relations
The mercury vapor lamp is a negative resistance device and requires auxiliary components (for example, a ballast) to prevent it from taking excessive current. Negative resistance (or negative differential resistance (NDR or differential negative resistance (DNR is a property of Electrical circuit elements composed An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads An electrical ballast (sometimes called control gear) is a device intended to limit the amount of current in an electric Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. The auxiliary components are substantially similar to the ballasts used with fluorescent lamps. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor. It is used often for outside lighting (signs) and for auditoriums and stages.
Also like fluorescent lamps, mercury vapor lamps usually require a starter which is usually contained within the mercury vapor lamp itself. Fluorescence is a Luminescence that is mostly found as an A third electrode is mounted near one of the main electrodes and connected through a resistor to the other main electrode. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | When power is applied, there is sufficient voltage to strike an arc between the starting electrode and the adjacent main electrode. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical This arc discharge eventually provides enough ionized mercury to strike an arc between the main electrodes. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Occasionally, a thermal switch will also be installed to short the starting electrode to the adjacent main electrode, completely suppressing the starting arc once the main arc strikes.
Variation: Metal halide
A closely-related lamp design called the metal halide lamp uses various other elements in an amalgam with the mercury. Metal halide lamps, a member of the High-intensity discharge (HID family of lamps produce high light output for their size making them a compact powerful and efficient Sodium iodide and Scandium iodide are commonly in use. Sodium iodide is a white Crystalline Salt with Chemical formula Na[[Iodine I]] used in radiation detection treatment of Iodine deficiency Scandium (ˈskændiəm is a Chemical element that has the symbol Sc and Atomic number 21 Iodine (ˈaɪədaɪn ˈaɪədɪn or /ˈaɪədiːn/ from ιώδης iodes "violet" is a Chemical element that has the symbol I and Atomic These lamps can produce much better quality light without resorting to phosphors. If they use a starting electrode, there is always a thermal shorting switch to eliminate any electrical potential between the main electrode and the starting electrode once the lamp is lit. (This electrical potential in the presence of the halides can cause the failure of the glass/metal seal). More modern metal halide systems do not use a separate starting electrode; instead, the lamp is started using high voltage pulses as with high-pressure sodium vapor lamps. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical "MetalArc" is Osram Sylvania's trademark for their metal halide lamps; "Arcstream" and "MultiVapor" are General Electric's trademark. OSRAM is part of the industry sector of Siemens AG and one of the two leading lighting manufacturers in the world Besides their use in traditional outdoor lighting, these lamps now appear in most computer and video projectors. A video projector takes a Video signal and projects the corresponding image on a Projection screen using a lens system However, Philips' UHP lamp, introduced in 1995, contains only mercury. Koninklijke Philips Electronics NV ( Royal Philips Electronics Inc. The Utah Highway Patrol (UHP is the Highway patrol agency for Utah, which has Jurisdiction anywhere in the state As an example of application and efficiency of mercury lamps, the 61" Samsung DLP rear projection TV (HL-S6187W) uses a 132 watt Philips UHP lamp.
Operation
When the lamp is first turned on, mercury-vapor lamps will produce a dark blue glow because only a small amount of the mercury is ionized and the gas pressure in the arc tube is very low, so much of the light is produced in the ultraviolet mercury bands. Blue is a Colour, the Perception of which is evoked by Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays As the main arc strikes and the gas heats up and increases in pressure, the light shifts into the visible range and the high gas pressure causes the mercury emission bands to broaden somewhat, producing a light that appears more-white to the human eye, although it is still not a continuous spectrum. White is a Color, the perception which is evoked by Light that stimulates all three types of color sensitive Cone cells in the Human eye In Physics, continuous spectrum refers to a range of values which may be graphed to fill a range with closely-spaced or overlapping intervals Even at full intensity, the light from a mercury vapor lamp with no phosphors is distinctly bluish in color.
Color considerations
To correct the bluish tinge, many mercury vapor lamps are coated on the inside of the outer bulb with a phosphor that converts some portion of the ultraviolet emissions into red light. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons This helps to fill in the otherwise very-deficient red end of the electromagnetic spectrum. The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies These lamps are generally called "color corrected" lamps. Most modern mercury vapor lamps have this coating. One of the original complaints against mercury lights was they tended to make people look like "bloodless corpses" because of the lack of light from the red end of the spectrum. There is also an increase in red color (e. g. , due to the continuous radiation) in ultra-high pressure mercury vapor lamps (usually greater than 200 atm. ) which has found application in modern compact projection devices.
Emission Line Spectrum (peaks) - 253. 7, 365. 4 (I-line), 404. 7 (H-line), 435. 8 (G-line), 546. 1, and 578. 2 nm.
Light pollution considerations
For placements where light pollution is of prime importance (for example, an observatory parking lot), low pressure sodium is preferred. Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects An observatory is a location used for observing terrestrial and/or celestial events Parking lot (called a car park in Australia and the UK) is a cleared area that is more or less level and is intended for Parking vehicles As it emits light on only one wavelength, it is the easiest to filter out. Mercury vapor lamps without any phosphor are second best; they produce only a few distinct mercury lines that need to be filtered out.
Ultraviolet hazards
All mercury vapor lamps (including metal halide lamps) must contain a feature (or be installed in a fixture that contains a feature) that prevents ultraviolet radiation from escaping. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Usually, the borosilicate glass outer bulb of the lamp performs this function but special care must be taken if the lamp is installed in a situation where this outer envelope can become damaged. Borosilicate glass is a type of Glass with the main glass-forming constituents Silica and Boron oxide. [1] There have been documented cases of lamps being damaged in gymnasiums. The word γυμνάσιον (gymnasion was used in Ancient Greece, meaning a locality for both physical and intellectual Education of young men (see Gymnasium Sun burns and eye inflammation have resulted. A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays [2] When used in locations like gyms, the fixture should contain a strong outer guard or an outer lens to protect the lamp's outer bulb. Also, special "safety" lamps are made which will deliberately burn out if the outer glass is broken. This is usually achieved by a thin carbon strip used to connect one of the electrodes, which will burn up in the presence of air. Combustion or burning is a complex sequence of Exothermic chemical reactions between a Fuel and an Oxidant accompanied by the production of
Even with these methods, some UV radiation can still pass through the outer bulb of the lamp. This causes the aging process of some plastics used in the construction of luminaires to be sped up, leaving them significantly discolored after only a few years' service. Polycarbonate suffers particularly from this problem; and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp to have turned a dull, 'ear-wax'-like color after only a short time. Certain polishes, such as Brasso, can be used to remove some of the yellowing, but usually only with a limited success. Brasso is one of the most widely-used and well-known Metal polishes in the world
End of life
Mercury vapor lamps rarely burn out completely but suffer from lumen depreciation and the bulb produces 50% less light output every five years, to the point of becoming ineffective while still drawing the same amount of power they drew when they were new. As well as decreased light output, the warm-up time the lamp is considerably increased, from the usual of 2 - 4 mins, up to 3 - 8 mins. Varying from bulb to bulb.
Uses
Photoresist Exposure
Ultra high pressure mercury vapor lamps are used in the area of photolithography to expose various photoresists. Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate Photoresist is a Light -sensitive material used in several industrial processes such as Photolithography and Photoengraving to form a patterned coating The unique spectral emission characteristics of mercury vapor lamps are ideal for photoresists, the most common of which are generally photosensitive between 350 and 500 nm wavelengths. Photoresist is a Light -sensitive material used in several industrial processes such as Photolithography and Photoengraving to form a patterned coating
See also
- List of light sources
- History of street lighting in the United States
- Mercury laser, a high-average-power laser system using the element mercury
References
- ^ http://www.sylvania.com/content/display.scfx?id=003690196
- ^ Thun, MJ; Altman R, Ellingson O, Mills LF, Talansky ML (Nov 1982). This is a list of sources of Light, including both natural and artificial sources and both processes and devices. The use of Street lighting was first recorded in the Arab Empire from the 9th-10th centuries especially in Cordoba, and then in London from The mercury laser is a high-average-power Laser system being developed as a prototype for systems to drive Inertial confinement fusion. "Ocular complications of malfunctioning mercury vapor lamps". Ann Ophthalmol. 14 (11): 1017-20. PMID : 7181332.
- Waymouth, John (1971). Electric Discharge Lamps. Cambridge, MA: The M. I. T. Press. ISBN 0-262-23048-8.
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