mercury-vapour lamp



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A 175W mercury-vapor yard light approximately 15 seconds after starting
A Mercury-vapor lamp is a gas discharge lamp which uses mercury in an excited state to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger 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 ultraviolet radiation, and a convenient mounting for the fused quartz arc tube.

Mercury vapor lamps (and their relatives) are often used because they are relatively efficient. Phosphor coated bulbs offer better color rendition than either high- or low-pressure sodium vapor lamps. They also offer a very long lifetime, as well as intense lighting for several applications.

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. The auxiliary components are substantially similar to the ballasts used with fluorescent lamps. 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. A third electrode is mounted near one of the main electrodes and connected through a resistor to the other main electrode. When power is applied, there is sufficient voltage to strike an arc between the starting electrode and the adjacent main electrode. This arc discharge eventually provides enough ionized mercury to strike an arc between the main electrodes. 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. Sodium iodide and Scandium iodide are commonly in use. 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. "MetalArc" is Osram Sylvania's trademark for their metal halide lamps; "Arcstream" and "MultiVapor" are General Electric's trademark. Besides their use in traditional outdoor lighting, these lamps now appear in most computer and video projectors. However, Philips' UHP lamp, introduced in 1995, contains only mercury. 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). 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). 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. This helps to fill in the otherwise very-deficient red end of the electromagnetic spectrum. 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.

Emits Wavelengths - 253.7, 365.4, 404.7, 435.8, 546.1, and 578.0 nm.

Light pollution considerations

For placements where light pollution is of prime importance (for example, an observatory parking lot), low pressure sodium is preferred. 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. 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.[1] There have been documented cases of lamps being damaged in gymnasiums and sun burns and eye inflammation have resulted.[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.

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.

End of life

At the end of life, mercury-vapor lamps commonly exhibit a phenomenon known as cycling. These lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge. As a lamp gets older, the maintaining voltage for 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.

See also

References

1. ^ [1]
2. ^ Thun, MJ; Altman R, Ellingson O, Mills LF, Talansky ML (Nov 1982). "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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Suigintou (水銀燈 Suigintō
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Gas discharge lamps are a family of artificial light sources that generate light by sending an electrical discharge through an ionized gas, i.e. a plasma. The character of the gas discharge critically depends on the frequency or modulation of the current: see the entry on a
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Lamp (from Greek λαμπάς: torch) can be:
  • An oil lamp, the original use of the term.
  • A portable light fixture such as a table lamp or reading lamp (common usage)

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2, 1
(mildly basic oxide)
Electronegativity 2.00 (scale Pauling)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.
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Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
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Fused quartz and fused silica are types of glass containing primarily silica in amorphous (non-crystalline) form. They are manufactured using several different processes.
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Borosilicate glass is a type of heat-resistant glass. Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century and sold under the brand name "Duran" in 1893.
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A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons).

The chemical element phosphorus (Greek.
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thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer.

Heat is transferred from one material to another by conduction, convection and/or radiation.
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Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. It is so named because the spectrum starts with wavelengths slightly shorter than the wavelengths humans identify as the color violet
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A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons).

The chemical element phosphorus (Greek.
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The Color Rendering Index (CRI) (sometimes called Color Rendition Index), is a measure of the ability of a light source to reproduce the colors of various objects being lit by the source. It is a method devised by the International Commission on Illumination (CIE).
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sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure.
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Negative resistance or negative differential resistance (NDR) is a property of electrical circuit elements composed of certain materials in which, over certain voltage ranges, current is a decreasing function of voltage.
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An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. Components are intended to be connected together, usually by soldering to a printed circuit board, to create an electronic circuit
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electrical ballast (sometimes called control gear) is a device intended to limit the amount of current flowing in an electric circuit.

Ballasts vary greatly in complexity. They can be as simple as a series resistor as commonly used with small neon lamps.
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Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.

Definition

The amount of electric current (measured in amperes) through some surface, e.g.
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fluorescent lamp is a gas-discharge lamp that uses electricity to excite mercury vapor in argon or neon gas, resulting in a plasma that produces short-wave ultraviolet light. This light then causes a phosphor to fluoresce, producing visible light.
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Fluorescence is a luminescence that is mostly found as an optical phenomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of another photon with a longer wavelength.
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Starter may refer to:
  • Automobile self starter, or motor starters, used to start large electrical motors
  • Fluorescent lamp Starter, used to jump start fluorescent lights since they require a charge in order to turn on (Refer to section 2.

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An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron
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resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: The electrical resistance
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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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 light source.
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amalgam is any mixture or blending of mercury with another metal or with an alloy. Most metals are soluble in mercury, but some (such as iron) are not. Amalgam also may be a solution of metal-like ion complexes, such as ammonium. Amalgams are commonly used in dental fillings.
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Sodium iodide is a white, crystalline salt with chemical formula NaI used in radiation detection, treatment of iodine deficiency, and as a reactant in the Finkelstein reaction.
H2O 184
Liquid ammonia 162
Liquid sulfur dioxide 15
Methanol 62.5 - 83.
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Scandium (IPA: /ˈskandiəm/) is a chemical element that has the symbol Sc and atomic number 21. A soft, silvery, white metal, scandium ore occurs in rare minerals from Scandinavia and elsewhere, and it is
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Iodine (IPA: /ˈaɪədaɪn, ˈaɪədɪn/, or /ˈaɪədiːn/; from Greek: iodes
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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