Electric lamp and discharge devices – With gas or vapor – Envelope composition
Patent
1995-11-20
1998-03-10
Patel, Ashok
Electric lamp and discharge devices
With gas or vapor
Envelope composition
313 25, 313573, 313571, H01J 6134, H01J 926
Patent
active
057265321
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a high-pressure discharge lamp as having a discharge vessel of quartz glass, surrounded by an outer bulb for producing such a high-pressure discharge lamp.
In particular, it relates to a high-pressure discharge lamp that is suitable for an optical projection system, such as for an automobile headlight.
BACKGROUND
European Patent Disclosure EP-A 0 570 068, Westemeyer et al., discloses such a lamp. It is used as a light source for an automobile headlight. This high-pressure discharge lamp has a quartz glass discharge vessel, sealed off on both ends on molybdenum fusing foils, with two electrodes aligned axially in it that are each fused into one end of the discharge vessel. An outer bulb of quartz glass surrounds the discharge vessel. FIG. 3 of this disclosure shows a high-pressure discharge lamp with a substantially rotationally symmetrical outer bulb, which is located coaxially with the discharge vessel and which outside the molybdenum fusing foils is fused with the sealed ends of the discharge vessel. With this type of fastening of the outer bulb, the danger is that when the outer bulb is fused to the discharge vessel ends, the molybdenum fusing of the discharge vessel will be damaged, and then the discharge vessel is no longer sealed in gas-tight fashion. This danger can be reduced in lamps in accordance with EP-A 0 570 068 by providing fusing of the outer bulb of the discharge vessel a sufficient distance away from the molybdenum foil seal.
European Patent Disclosure EP-A 0 465 083, Davenport et al., likewise describes a high-pressure discharge lamp of the type referred to. This high-pressure discharge lamp has a quartz glass discharge vessel, sealed off on two ends by means of molybdenum fusing seals, with two electrodes oriented axially inside it that are each fused into one end of the discharge vessel. Outside the fused-in molybdenum foils, the discharge vessel ends each have a platelike thickened portion, with which a quartz glass outer bulb surrounding the discharge vessel is fused in gas-tight fashion. This type of outer bulb fixation to the discharge vessel by means of the platelike thickened portions is comparatively complicated and expensive. Moreover, these platelike thickened portions must also be far enough away from the fused-in molybdenum foils that they do not threaten the sealing of the discharge vessel.
THE INVENTION
It is an object of the invention to provide a high-pressure discharge lamp as generically described above, especially being of small dimension, e.g. a low-wattage high-pressure discharge lamp up to an electrical power of approximately 150 W, which has a very simple and highly reliable attachment of the outer bulb to the discharge vessel, and to disclose a process for producing such a high-pressure discharge lamp.
Briefly, the high-pressure discharge lamps of the invention are equipped with an outer bulb, whose glass has lower viscosity and hence a lower softening temperature than the quartz glass of the discharge vessel and is fused to the pinch seals of the discharge vessel, preferably in the vicinity of the remote ends of molybdenum foils in the pinch seals. As a result, when the outer bulb is fused by melting to the discharge vessel, only the outer bulb glass but not the quartz glass of the discharge vessel softens. Because of the different softening temperatures, there is hence no danger that the sealed discharge vessel ends will be melted again and damaged when the outer bulb is fused on. It is even possible for the outer bulb to be fused directly to the pinch seals of the discharge vessel ends, without impairing the seal of the discharge vessel ends, which seal includes the molybdenum foils embedded in the seal. As a result, the structural length of the high-pressure discharge lamp according to the invention can be shortened, in comparison with the lamps cited above as prior art.
Advantageously, the outer bulb is made of a soft quartz glass provided with viscosity-reducing additives, while the thermally more sever
REFERENCES:
patent: 5196759 (1993-03-01), Parham et al.
patent: 5229681 (1993-07-01), Gordin et al.
patent: 5572091 (1996-11-01), Langer et al.
patent: 5589734 (1996-12-01), Deisenhofer et al.
Lang Dieter
Wittig Christian
Patel Ashok
Patent-Treuhand-Gesellschaft F. Elektrische Gluehlampen mbH
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