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Mercury Projection
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Updated
16-XII-2022 |
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The high intrinsic brightness of the mercury vapour discharge at once attracted the interest of optical engineers, to create a more effective lamp for image projection applications than had been possible with tungsten filament technologies. Early variants consisted of the arc tubes of MB High Pressure lamps sealed into a compact clear outer bulb, to enable it to be brought closer to an optical system.
Efforts then focussed on overpowering these lamps at still higher pressure to achieve even greater brightness, but soon reached the limits of strength of the quartz arc tubes. In 1935 Philips of the Netherlands developed the MD class of Capillary lamps, whose pressure is typically in the range 50-200 atmospheres with a power dissipation >100W per cm. To prevent immediate destruction of the quartz arc tube, its outer surface must be chilled by a flow of water having sufficiently high velocity to prevent the water from boiling. Despite such extreme measures, the life of MD lamps is rather short. Failure is due to devitrification of the inner surface of the arc tube, which may either become so opaque that the intensity falls off and the lamp becomes useless for its application, or it will become sufficiently weakened that it cannot contain the internal pressure and will explode. Despite the immensely high pressure within the arc tube the explosion is not particularly violent in view of the small tube volume. Typical service life is of the order of fifty hours.
Almost in parallel with the Dutch development of MD lamps, the British and Germans explored an alternative concept consisting of an extremely short arc within a spherical thick-walled quartz arc tube. That work led to introduction of the ME Short Arc lamps, having power loadings in the region of 1000 watts per centimetre of arc length and mercury pressures of around 25-100 atmospheres. The reduced thermal loading of the enlarged spherical arc tubes obviated the need for complex water cooling, and dramatically extended lamp life. ME lamps were produced in a wide variety of powers from 50W to 25,000W, sometimes with the addition of cadmium to increase the red ratio (type MEC lamps). Such lamps have an extremely rich shortwave ultraviolet spectrum, which makes them the favoured radiation sources for microlithographic printing in the semiconductor industry. Following the development of metal halide lamps, the pure mercury short arc ME types were almost completely supserseded by the MEI class containing metal iodide salts to improve the colour rendering.
Around the turn of the last century, there was a return to pure mercury discharges running at Ultra High Pressures above 200 atmospheres. Their benefit over metal halide types is an improved spatial colour uniformity, and the fact that their arc gap can be made much shorter. This is of profound importance in digital image projection devices, a technology which became commonplace largely thanks to the development of this remarkable projection light source. |
| | High Pressure |
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GEC |
80W |
| MB/D Projector lamp with handmade arctube |
| 1942 |
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GE |
85W |
| H85A3/UV Lab-Arc Ultraviolet Source |
| 1952 |
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Mazda |
80W |
| MB/D for monochrome slide projection |
| 1962 |
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Mazda |
125W |
| MBL/D with diaphragms for laboratory use |
| 1967 |
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Philips |
125W |
| HPK 125 for laboratory use |
| 1975 |
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| | High Pressure Capillary |
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Mazda |
1000W |
| MD/H arc tube with water jacket |
| 1947 |
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Philips |
500W |
| SP500 arc tube mounted in reflector housing |
| 1961 |
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GE |
1000W |
| AH-6 Super pressure water-cooled arc tube |
| 1961 |
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ARC |
1000W |
| Mercury Capillary with curved & coated tube |
| ~2000 |
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| | High Pressure Short Arc |
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Osram |
250W |
| ME/D Compact Source Glass 3-Pin style |
| 1959 |
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Mazda |
250W |
| ME/D Compact Source Glass 3-Pin style |
| 1963 |
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Thorn |
250W |
| ME/D Compact Source Glass Pre-focus style |
| 1980 |
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Osram |
250W |
| ME/D Compact Source Metal box 3-Pin style |
| 1964 |
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Mazda |
250W |
| ME/D Compact Source Metal box Prefocus style |
| 1950 |
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Osira |
500W |
| ME/H Bombing Teacher Glass Pre-focus style |
| 1945 |
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Westinghouse |
250W |
| SAH-250B Short Arc DC Mercury |
| 1942 |
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Osram |
3500W |
| HBO deep UV source for semiconductr fabrication |
| 2000 |
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| | Ultra High Pressure |
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Philips |
120W |
| UHP 120W projector First Generation lamp |
| 1995 |
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Philips |
120W |
| UHP 120W for LCD Video Projector |
| 2001 |
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