Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
1999-03-16
2001-07-17
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S311000
Reexamination Certificate
active
06262533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high pressure discharge lamp such as a sodium-vapor lamp, a metal halide lamp or the like.
2. Background Art
Conventionally, a high pressure discharge lamp includes a vessel made of a non-conductive material which forms an inner space filled with an ionizable light-emitting material and a starting gas, the vessel having first and second opening portions at both ends thereof, and a non-conductive member inserted into the first opening portion of the vessel and having an outer diameter which is smaller than inner diameter of the first opening portion so as to form a gap between the vessel and the non-conductive member, the non-conductive member further having a hole. An electrode unit is inserted into the hole of the non-conductive member. The electrode unit has a first end which is exposed to the inner space of the vessel, and a second end which is exposed to outside of the vessel.
In this connection, GB-A-1421406, JP-U-52-19182 and U.S. Pat. No. 5,541,480 each discloses such a high pressure discharge lamp which is further provided with at least one starting electrode which serves to reduce the starting voltage.
In the high pressure discharge lamp according to GB-A1421406, the non-conductive member is in the form of a ring which is inserted into a gap between an envelope and a cap, and a metal layer is provided on an inner face of the ring and acts as a starting electrode. In this instance, since the ring is arranged between the envelope and the cap, it is necessary to seal the gap between the envelope and the ring, and also seal the gap between the ring and the cap. Such a structure is not very appropriate from the viewpoint of the corrosion resistance and the tightness property.
In the high pressure discharge lamp according to JP-U-52-19182 and U.S. Pat. No. 5,541,480, a linear conductive material such as carbon, platinum, palladium or the like is provided on a light-emitting portion thereof. This structure is not very appropriate because such a conductive material tends to decrease the luminous flux of the lamp.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a high pressure discharge lamp which has excellent corrosion resistance and tightness properties without reducing the luminous flux.
According to the present invention of the high pressure discharge lamp, there is provided a high pressure discharge lamp comprising: a vessel made of a non-conductive material which forms an inner space filled with an ionizable light-emitting material and a starting gas, the vessel having first and second opening portions at both ends thereof, a non-conductive member inserted into the first opening portion of the vessel and having an outer diameter which is smaller than inner diameter of the first opening portion so as to form a gap between the vessel and the non-conductive member, the non-conductive member further having a hole; an electrode unit inserted into the hole of the non-conductive member, the electrode unit having a first end which is exposed to the inner space of the vessel, and a second end which is exposed to outside of the vessel; and an starting electrode arranged in the gap between the vessel and the non-conductive member, and having a first end which is exposed to the inner space, and a second end which is exposed to outside of the vessel; the vessel, the non-conductive member and the starting electrode being an integrated body which has been formed by a co-firing process.
According to the invention, the starting electrode is arranged in the gap between the vessel and the non-conductive member, it has a first end which is exposed to the inner space and a second end which is exposed to outside of the vessel, the vessel, the non-conductive member and the starting electrode is an integrated body which has been formed by a co-firing process. Therefore, it is not necessary to provide another member when the starting electrode is provided and seals the gap therebetween, so that the discharge lamp according to the invention has excellent corrosion resistance and tightness properties. Also, as carbon, platinum, palladium or the like is not provided on an outer surface of a light-emitting portion thereof the luminous flux thereof does not decrease. Moreover, such a integrated body makes a strongly jointed structure thereamong. As used in the embodiment, the phrase “the non-conductive member” includes a capillary, a disc or both of them.
Preferably, the starting electrode is composed of a metal.
By composing the starting electrode of a metal, a good conductivity thereof the connection between the starting electrode and an outer circuit, and a good discharge by the starting electrode are realized.
The starting electrode can also be composed of a mixture of a non-conductive material and a metal.
By composing the starting electrode by the mixture, the non-conductive material in the vessel and the non-conductive member is diffused into the mixture when having been subjected to a co-firing into an integrated body, so that a strongly jointed structure is formed among the starting electrode, the vessel and the non-conductive member. Therefore, the present invention yields a discharge lamp having full tightness characteristics while maintaining full conductivity.
More preferably, the mixture contains 30 to 70 volumetric percentage of a metal.
As the volumetric percentage of a metal increases, the conductivity of the starting electrode improves. On the other hand, as the volumetric percentage of a non-conductive material increases, the tightness property of the discharge lamp improves. To compromise these properties, it is found that 30 to 70 volumetric percentage of a metal is preferable.
More preferably, the metal of the mixture contains not less than 50 volumetric percentage of molybdenum; and the non-conductive material of the mixture contains not less than 50 volumetric percentage of the material from which the vessel and/or the non-conductive member is formed.
To form a strongly jointed structure among the starting electrode, the vessel and/or the non-conductive member, it is necessary to select a metal having a melting point near that of the non-conductive material which composes the vessel and/or the non-conductive member, and a high halogen resistance. Also, the non-conductive material of the mixture used to make up the starting electrode should be formed of the material which the vessel and/or the non-conductive member is formed. To fulfill such requirements, the metal contains not less than 50 volumetric percentage of molybdenum which has a high halogen resistance and a comparatively low melting point (2623° C.), and the non-conductive material contains not less than 50 volumetric percentage of the material from which the vessel and/or the non-conductive material is formed.
More preferably, the metal of the mixture forming the starting electrode comprises molybdenum, and the non-conductive material of the mixture is the same as the non-conductive material for said vessel and said non-conductive member.
To form a strongly jointed structure among the starting electrode, the vessel and/or the non-conductive member, it is preferable that the volumetric percentage of molybdenum in the metal be as high as possible, and that of the non-conductive material which the vessel and/or the non-conductive member is formed, also be as high as possible. Therefore, it is preferred that the mixture comprises molybdenum and the material which the vessel and the non-conductive member are formed.
As used herein, the word “molybdenum” includes not only pure molybdenum, but also molybdenum which contains a small amount of impurities. Also, the phrase “material which the vessel and the non-conductive material are formed” not only the pure material which the vessel and non-conductive member are formed but also a material which contains a small amount of impurities.
Further, the starting electrode may comprise an exposed portion which is exposed to either the inner space or outside of s
Burr & Brown
Hopper Todd Reed
NGK Insulators Ltd.
Patel Ashok
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