Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
1998-12-22
2001-03-27
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S025000, C313S634000
Reexamination Certificate
active
06208070
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a metal vapor discharge lamp using a ceramic material for the discharge tube.
BACKGROUND OF THE INVENTION
A conventional high-pressure metal vapor discharge lamp using a ceramic material for the discharge tube is disclosed, for example, in Publication of Unexamined Japanese Patent Application No. Hei 6-196131.
This conventional high-pressure metal vapor discharge lamp uses a discharge tube where the two ends of a cylindrical portion are plugged with disks by shrinkage fitting. Regardless of the lamp orientation of this high-pressure metal vapor discharge lamp during operation, in other words for vertical operation, where the metal vapor discharge lamp is arranged so that the axes direction of the electrodes point in a vertical direction, as well as for horizontal operation, where the metal vapor discharge lamp is arranged so that the axes of the electrodes point in a horizontal direction, a condensed phase of the excess discharge metal compound is present in the shrinkage-fitted plug portion. Thus, a high-pressure metal vapor discharge lamp whose operating characteristics are independent from the lamp orientation can be obtained.
However, since in this conventional high-pressure metal vapor discharge lamp the ends of two cylindrical portions of the discharge tube are plugged with disks by shrinkage fitting, the airtightness of the plug portion is not very reliable, and the lamp characteristics cannot be maintained sufficiently over long-term use.
Another configuration that has been proposed for high-pressure metal vapor discharge lamps using a ceramic discharge tube relates to a discharge tube with cylindrical portions and tapered portions, wherein the ends of two cylindrical portions are plugged by shrinkage fitting without disks. This high-pressure metal vapor discharge lamp can ensure airtightness with higher reliability, because the discharge tube is shrinkage-fitted without disks. However, its operating characteristics depend on the lamp orientation, and vary when the position of the condensed phase of the excess discharge metal compound changes.
It is an object of the present invention to solve the problems of the prior art. It is a further object of the present invention to provide a metal vapor discharge lamp wherein (a) the discharge tube does not include disks among its parts and (b) the shape of the discharge tube is optimized, so that good operating Characteristics are maintained over long-term use, and the operating characteristics depend only little on the lamp orientation.
SUMMARY OF THE INVENTION
In order to achieve this purpose, a metal vapor discharge lamp in accordance with the present invention comprises a discharge tube comprising a container made of ceramic. The ceramic container has a first cylindrical portion; second cylindrical portions with an outer diameter that is smaller than an inner diameter of the first cylindrical portion; third cylindrical portions with and outer diameter that is substantially the same as an inner diameter of the second cylindrical portion; and tapered portions having an inner surface. The ceramic container contains a discharge metal compound sealed into the ceramic container. The metal vapor discharge lamp further comprises a pair of electrodes having first ends and second ends arranged in the ceramic container. The first cylindrical portion, the tapered portions and the second cylindrical portions are formed in one piece. Each of the third cylindrical portions is attached to one of the second cylindrical portions. The first ends of the pair of electrodes oppose each other inside the ceramic container. The second ends of the pair of electrodes are attached and sealed into the third cylindrical portions using a sealing member. An inner wall of the third cylindrical portions and the electrodes define a gap. The inner surface of the tapered portions and a central axis of the electrodes define an angle of 40°-80°.
This configuration raises the reliability with regard to airtightness compared to conventional configurations, which used disks for the sealing by shrinkage-fitting, because the first cylindrical portion, the second cylindrical portions and the tapered portions are formed in one piece. Moreover, a lamp whose characteristics do not depend on its orientation can be attained, because the inner surface of the tapered portions and a central axis of the electrodes define angle of 40°-80°.
It is preferable that the metal vapor discharge lamp satisfies
0.85 d≦D≦0.95 d.
wherein d (mm) in an inner diameter of the third cylindrical portions and D (mm) is an outer diameter of at least a portion of the electrodes.
This configuration makes it possible to obtain a metal vapor discharge lamp with a long lifetime whose operating characteristics depend only little on the lamp orientation, because the condensed phase of the discharge metal compound does not easily enter the space between the electrodes and the third cylindrical portions during lamp operation.
It is preferable that an axial length L (mm) of the gap defined by the inner wall of the third cylindrical portions and the electrodes of the metal vapor discharge lamp is 3 mm≦L≦10 mm.
If the axial length of the gap is less than 3 mm, the end face of the sealing member in the third cylindrical portion is close to the discharge space, so that the lamps lifetime is shortened due to the reaction between the sealing member and the discharge metal compound. On the other hand, if the axial length of the gap is more than 10 mm, the amount of the condensed phase of the discharge metal compound that enters the gap between the electrodes and the third cylindrical portions during operation becomes too large, so that the desired initial lamp characteristics cannot be attained. Consequently, in the present invention, it is preferable that that the axial length of the gap is within the above-mentioned range.
Moreover, it is preferable that the sealing member of the metal vapor discharge lamp comprises a cermet. This preferable configuration makes it possible to obtain a metal vapor discharge lamp that is very resistant against thermal shocks that occur, for example, when the discharge tube is sealed or when the lamp is turned on or off. This is because the cermet plugs have an expansion coefficient that is closer to the expansion coefficient of the ceramic of the discharge tube than the feed portions.
REFERENCES:
patent: 4734612 (1988-03-01), Sasaki et al.
patent: 4749905 (1988-06-01), Mori et al.
patent: 5416383 (1995-05-01), Genz
patent: 5424609 (1995-06-01), Geven et al.
patent: 0 215 524 (1987-03-01), None
patent: 0 587 238 (1994-03-01), None
patent: 0 841 687 (1998-05-01), None
patent: 62-283543 (1987-12-01), None
patent: 9-283083 (1997-10-01), None
Nakayama Shiki
Nishiura Yoshiharu
Nohara Hiroshi
Sugimoto Kouichi
Takeda Kazuo
Matsushita Electronics Corporation
Merchant & Gould P.C.
Patel Vip
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