Electric lamp and discharge devices – With gas or vapor – Having particular electrode structure
Patent
1989-01-13
1990-06-26
O'Shea, Sandra L.
Electric lamp and discharge devices
With gas or vapor
Having particular electrode structure
313620, 313637, 313643, 372 69, H01J 1706, H01J 6116, H01S 309
Patent
active
049374966
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a xenon short arc discharge lamp having a high-pressure-proof bulb, at least the transparent zone of which comprises quartz glass. Two opposed rod-shaped electrodes located on one axis protrude into the bulb, and the anode has a larger diameter than the cathode. The bulb has a fill pressure of at least one bar in the non-operating state and an electrode spacing that is shorter than the diameter of the shaft of the cathode.
BACKGROUND
Short arc lamps, in particular xenon high-pressure short arc lamps, have the highest radial intensities per unit area of all known lamps, as well as an arc of very small diameter and very short length. To a good approximation, they are punctiform light sources, and are correspondingly used in projection systems of all kinds, such as film projectors, arc furnaces, photolithography, and in other optical equipment having high radiant intensities per unit area. They include a high-pressure-proof bulb with a spherical or ellipsoid discharge space, for instance of quartz glass; electrodes that as anodes and cathodes are connectable to a source of direct voltage, and comprise tungsten or tungsten with additives; and current ducts fused into the bulb, such as single or multiple molybdenum ribbon ducts or molybdenum cap ducts. Known short arc lamps may include fillings of xenon, mercury, argon, tin or zinc. A mercury lamp requires several minutes to warm up to full operating pressure and light output. This warm-up time is reduced by about 50 percent if xenon at a pressure exceeding one atmosphere is added to the mercury.
From British Patent No. 1,603,699, a short arc lamp of this type filled with xenon and mercury is known. For the electrode spacings in such lamps, which are also known as electrode-stabilized discharge lamps, figures of less than 10 mm to less than 1 mm are given.
A xenon short arc discharge lamp with a bulb of quartz glass and two opposed rod-shaped electrodes is also known from the journal "Illuminating Engineering", Vol. 59, 1964, No. 9, pp. 589-591. The anode has a larger diameter than the cathode; the electrode spacing is shorter than the shaft of the cathode, and the cathode tip is conical.
In the journal "Applied Optics", Vol. 10, 1971, No. 11, pp. 2517-2520, a xenon discharge lamp is described which may contain, in addition to xenon, a doping substance such as thallium iodide.
A xenon short arc discharge lamp is also known from Swiss Patent No. 297 983, in which the electrodes are as close as from 0.5 to 2 mm to one another, so that the positive column of the discharge is suppressed, and the lamp radiates only in the cathode spot. The lamp filling, which is of heavy noble gas (xenon), may have a doping gas having an atomic weight of less than 21 added to it.
In a such a case, the doping merely causes an additional appearance of spectral lines of the doping substance at reduced plasma temperature.
THE INVENTION
Based on the known short arc discharge lamps, it is the object of the invention to increase the radiant intensity per unit area of previously known short arc lamps considerably, the goal being as punctiform a discharge zone as possible, without blackening of the lamp bulb and without sacrifices in terms of burn stability.
This object is attained in accordance with the invention by. The term metal halides is also understood to include the rare earth metal halides.
In a preferred embodiment, the bulb of the lamp is completely of quartz glass. Metal halides have been inserted as doping substances. The use of thallium iodide as doping material has proved to be particularly suitable, because with it a lowering of the plasma temperature can be avoided. Instead, the plasma temperature can be increased, and thus the radiant intensity per unit area as compared with an undoped lamp is also increased. The increase of the radiant intensity per unit area is due substantially to a considerable increase in the continuum emission.
When metal iodides are used as the doping additive, a halide circuit (tungsten-halogen cycle process) is advant
REFERENCES:
patent: 1334150 (1920-03-01), Green et al.
patent: 3259777 (1966-07-01), Fridrich
patent: 3706000 (1972-12-01), Retzer et al.
patent: 3714493 (1973-01-01), Fridrich
patent: 3902090 (1975-08-01), Ekkelboom
W. Thouret et al., "High-Brightness Xenon Lamps", Sep. 1964 Illuminating Engineering, vol. 9, pp. 589-591.
C. F. Gallo, Applied Optics, vol. 10, No. 11, Nov. 1971, "Continuum Emission Spectra from Long Linear Xenon Lamps".
K. Luttio et al., "Xenon Short Arc Lamps . . . " Soc. Motion Picture & TV Eng. Jour., Feb. 1983, vol. 92, No. 2.
Hoppstock Reiner
Kleiner Bernd
Neiger Manfred
O'Shea Sandra L.
W. C. Heraeus GmbH
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