Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1999-05-12
2001-01-30
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S624000, C313S570000
Reexamination Certificate
active
06181064
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a high pressure discharge lamp of the direct current operating type.
2. Description of the Related Art
The high pressure discharge lamp of the direct current operating type shown in
FIG. 1
is known as a high pressure discharge lamp which is used, for example, for a light source in irradiation with UV radiation. Here, an discharge vessel
91
of fused silica glass has opposite sides of a arc tube portion
91
C joined to hermetically sealed portions
91
A and
91
B. Furthermore, this lamp has a metal foil
92
A which is inserted in the hermetically sealed portion
91
A of the discharge vessel
91
, and a metal foil
92
B which is inserted in the hermetically sealed portion
91
B of the discharge vessel
91
. In addition, this lamp has a pin-shaped anode
93
A and a pin-shaped cathode
93
B. The anode
93
A is attached in the hermetically sealed portion
91
A with its base connected to the metal foil
92
A, and its tip projecting into the arc tube portion
91
C. Similarly, the cathode
93
B is attached in the hermetically sealed portion
91
B with its base connected to the metal foil
92
B, and its tip projecting into the arc tube portion
91
C. Still further, this lamp has a supply lead
94
A and a supply lead
94
B, the supply lead
94
A being attached in the hermetically sealed portion
91
A with its inner end connected to the metal foil
92
A and its outer end projects outwardly from the discharge vessel
91
, the supply lead
94
B being attached in the hermetically sealed portion
91
B with its inner end connected to the metal foil
92
B and its outer end projecting outwardly from the discharge vessel
91
.
In Japanese patent disclosure document SHO 61-263040 of the assignee of the present application, a technology is disclosed in which, in the above described high pressure discharge lamp of the direct current operating type, there are conductive components on the cathode side on the area of the outer surface of the hermetically sealed portion surrounding the metal foil and these components are used to maintain the hermetic property between the hermetically sealed portion (
91
B) on the cathode side and the metal foil (
92
B). In this technology, these conductive components are furthermore electrically connected to the metal foil.
In this technology, the electrical potential of the conductive component during lamp operation becomes the same as the electrical potential of the metal foil. In this way, a hermetic connection between the metal foil and the fused silica glass in the hermetically sealed portion is preserved.
However, in the high pressure discharge lamp known in the prior art, including the lamp described in the above described patent disclosure document, it is considered a disadvantage that the strength of the area of the fused silica glass which forms the discharge vessel and which is in contact with the pin-shaped cathode (the contact surface with the cathode rod and its vicinity) deteriorates over time as lamp operation continues and often fractures originate from this area.
Therefore, it is a good idea to prevent fractures originating from the contact area with the cathode rod and to improve the service life of the high pressure discharge lamp.
SUMMARY OF THE INVENTION
The invention was devised to eliminate the above described defect in the prior art. Thus, a primary object of the present invention is to provide a high pressure discharge lamp in which, in the silica glass which comprises the discharge vessel, no fractures arise originating from the contact area with the cathode.
As a result of dedicated research, the present inventor has found that the fractures in the silica glass of the discharge vessel that originate from the contact area with the cathode are based on the mechanism described below:
In lamp operation, cations which are present as impurities in the silica glass are sucked up by the cathode. Thus, they move and reach the contact area with the cathode. Due to these cations, micro cracks inevitably form in the contact area with the cathode, by which the silica glass in this contact area is adversely affected (strength is reduced). This is the main factor in the fractures originating from the contact area with the cathode.
The inventor has found that the movement of the cations in the silica glass in the hermetically sealed portion to the contact area with the cathode can be prevented and suppressed by the conductive component on the cathode side, over the entire area of the outside surface of the hermetically sealed portion surrounding the cathode, being in a state in which adhesion is not complete (i.e., in a state in which microscopically small glass surfaces project). The inventor has devised the invention based on this finding.
The object is achieved, in accordance with the invention, in a high pressure discharge lamp of the direct current operating type which comprises:
a discharge vessel of silica glass in which opposite sides of an arc tube portion are joined to hermetically sealed portions;
a metal foil which is inserted in the first hermetically sealed portion on the first side of the arc tube portion;
an anode, which is attached to the first hermetically sealed portion which is located on the above described first side, has a base which is connected to the metal foil and a tip which projects into the arc tube portion;
a supply lead is attached by the first hermetically sealed portion, which is located on the first side, has an inner end connected to the metal foil and an outer end which projects to the outside from the discharge vessel;
a metal foil which is inserted in the hermetically sealed portion on the second side of the arc tube portion;
a cathode, which is attached by the hermetically sealed portion which is located on the other second side, has a base which is connected to the metal foil and a tip which projects into the arc tube portion; and
a supply lead, which is attached in the second hermetically sealed portion which is located on the second side, has an inner end connected to the metal foil and an outer end which projects to the outside from the discharge vessel;
wherein a conductive component completely encloses the outer surface of the second hermetically sealed portion on the second side in the area which surrounds the cathode, and in the area of the outer surface which this conductive component encloses, there are microscopically small glass surfaces which project on the outer surface but are not contacted by the at least one conductive component.
The object is furthermore advantageously achieved in accordance with the invention in a high pressure discharge lamp by the conductive component being made of metal wire with which the hermetically sealed portion on the second side is wound.
The object is furthermore advantageously achieved in a high pressure discharge lamp by the arc tube portion being filled with at least 0.13 mg/mm
3
mercury, rare gas and halogen and by the wall load being at least 0.8 W/mm
2
.
The conductive component which is located in the area of the outer surface of the hermetically sealed portion of the discharge vessel and which surrounds the cathode (area which is adjacent to the arc tube) is irradiated with UV radiation from the arc tube portion.
Photoelectrons which are held on the microscopically small projecting glass surfaces and which are not contacted by the conductive component are emitted from the conductive component which was irradiated with UV radiation. In this way, the area of the outer surface of the second hermetically sealed portion (the area which surrounds the cathode) which is provided with conductive component is negatively charged. As a result, the cations in the silica glass are prevented and suppressed from being sucked up by the contact area with the cathode and from moving. Therefore, micro cracks present in this contact area are prevented from growing (the silica glass is prevented from being adversely affected).
Furthermore, the outer surface of the hermetically sealed portion is negative
Nixon & Peabody LLP
Patel Ashok
Safran David S.
Ushiodenki Kabushiki Kaisha
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