Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Patent
1996-05-30
1997-11-18
Patel, Ashok
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
313113, 313116, H01J 6130, H01J 6135
Patent
active
056891547
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is based on a metal halide gas discharge lamp, particularly suitable for video projection, endoscopy, or for medical technology, e.g. operating room lights.
They are especially suitable for video projection using liquid crystal technology (LCD), and especially for large-picture television screens with an aspect ratio of 16:9. Typical power ratings are from 100 to 1500 W.
BACKGROUND
The lamps suitable for these uses must have not only a high light yield but above all good to very good color reproduction. This is true particularly in combination with reflectors of the kind used for projection purposes. Uniform distribution of luminance and color over the projection surface is of great importance in that case.
U.S. Pat. No. 5,220,237, Maseki et al, to which European Patent Application EP-A 0 459 786 corresponds, discloses this kind of lamp with a reflector. To meet the stated requirements, the surface of the discharge vessel, in the region of a first electrode, has a reflecting/thermal insulating film--hereinafter, "heat buildup coating" for short. This is immediately followed by a region where the surface is frosted. This region extends at least as far as the middle between the two electrodes and at most as far as the middle of a wire wound around the second electrode. The lamp is designed to be installed axially in a reflector. Perpendicular to the reflector axis, one or optionally both of the arc cores that occur in the immediate vicinity of the electrode in alternating current operation is covered by the frosting. A disadvantage is that as a result a considerable portion of the radiation originating at these arc cores is lost to projection through the reflector because of scattering at the frosted portion. As a result, the effectively usable light yield of the lamp and reflector system also drops.
THE INVENTION
It is an object of the present invention is to eliminate this disadvantage and to provide a lamp for projection purposes with a better light yield that is moreover distinguished by homogeneous color distribution, good color reproduction, and a long service life.
Briefly, the frosting of the surface of the discharge vessel is limited to a region or a strip between the electrodes. The width of the frosted surface is smaller than, or at most the same width as, the spacing of the electrodes. A region of the bulb with a clear surface adjoins the frosted region. It is thus assured that a great majority of the radiation of both arc cores will pass as oriented radiation through the clear or in other words unfrosted surface. It can then be efficiently projected optically with the aid of a suitable reflector, e.g. a parabolic reflector. By suitable selections the width of the frosted surface and the roughness of the frosting, a compromise can be attained between the light flux and the uniformity of the illumination. Depending on requirements, the quotient of the width B of the frosted surface and the spacing d of the electrodes can vary in the range of 0.1 <B/d.ltoreq.1. Particularly good results are attained with quotients between 0.4 and 0.8. Preferably, the frosting is applied to the surface of the discharge vessel centrally between the electrodes.
The advantage of the invention becomes clear if one compares the drop in light flux of a lamp caused by conventional frosting--as taught by EP-A 0 459 786--to that resulting from frosting according to the invention. While in the first case, and according to the prior art, the usable light flux drops to 65% from a clear lamp, a comparable lamp according to the invention, with identical uniformity of the illumination, still attains typically 80% of the light flux of the unfrosted lamp.
The discharge vessel comprises a translucent material, such as quartz glass. It is hermetically sealed on two ends, for instance by pinch seals, and can be coated on one or both ends with a heat buildup coating. An important characteristic is that in each case, both edges of the frosted surface are initially adjoined by a clear or in o
REFERENCES:
patent: 4281267 (1981-07-01), Johnson
patent: 4701664 (1987-10-01), Larue et al.
patent: 5220237 (1993-06-01), Maseki et al.
patent: 5363007 (1994-11-01), Fromm et al.
Barthelmes Clemens
Dittrich Thomas
Seedorf Ralf
Patel Ashok
Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH
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