Electric lamp and discharge devices – With temperature modifier – Double wall – jacket or casing for envelope
Reexamination Certificate
2001-01-12
2002-11-19
Wong, Don (Department: 2821)
Electric lamp and discharge devices
With temperature modifier
Double wall, jacket or casing for envelope
C313S623000
Reexamination Certificate
active
06483230
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a high-pressure metal vapor discharge lamp having a discharge tube made of transparent ceramics.
BACKGROUND ART
Conventionally, high-pressure metal vapor discharge lamps of this type often are known to have a quartz discharge tube as shown in FIG.
9
. In other words, a quartz discharge tube
34
having a pair of main electrodes
31
and
32
and an auxiliary electrode
33
therein is provided, and the auxiliary electrode
33
is disposed next to the main electrode
32
. The discharge tube
34
also has a discharge portion
35
as a discharge space and sealing portions
36
and
37
that are provided at both ends of the discharge portion
35
. In the sealing portions
36
and
37
, electrode rods
38
and
39
supporting the main electrodes
31
and
32
at their tips, metal foils
40
and
41
that are made of molybdenum and whose one end is connected to the rear end of the electrode rods
38
and
39
and external lead wires
42
and
43
whose one end is connected to the other end of the metal foils
40
and
41
are integrated to be current supply conductors for the main electrode, and an auxiliary electrode rod
44
supporting the auxiliary electrode
33
at the tip, a metal foil
45
that is made of molybdenum and whose one end is connected to the rear end of the auxiliary electrode rod
44
and an external lead wire
46
whose one end is connected to the other end of the metal foil
45
are integrated to be a current supply conductor for the auxiliary electrode. The current supply conductors for the main electrode and the current supply conductor for the auxiliary electrode are sealed by crushing so that the main electrodes
31
and
32
and the auxiliary electrode
33
at their tips are located in the discharge portion
35
. Also, a Ne—N
2
mixed gas is sealed in an outer tube
2
.
When starting the operation of such a high-pressure metal vapor discharge lamp, an auxiliary discharge first is generated between the main electrode
32
and the auxiliary electrode
33
provided next to this main electrode
32
, followed by a transition to a main discharge between the main electrodes
31
and
32
.
In particular, metal halide lamps, which are one type of the high-pressure metal vapor discharge lamps having the above-described structure, are used widely as ones to which inexpensive ballast for mercury lamps are applicable.
JP 62(1987)-150646 A, directed to a ceramic discharge lamp, discloses a ceramic discharge tube with the following structure. That is, as shown in
FIG. 10
, electrically conductive cermet disks
53
a
and
53
b
supporting main electrode rods
52
a
and
52
b
are sealed air-tight at the ends of a discharge tube
51
. The disk
53
a
supports an auxiliary electrode
54
so that the auxiliary electrode
54
is insulated from the main electrode rod
52
a
via an insulating layer
55
.
Also, JP 10(1998)-106491 A, directed to a high-pressure metal vapor discharge lamp, discloses the following structure. That is, a discharge tube
61
is disclosed to have a structure in which, as shown in
FIG. 11
, transparent ceramic disks
64
a
and
64
b
provided with slender ceramic tubes
63
a
and
63
b
in which electrode lead-in wires
62
a
and
62
b
as electrode lead-in members are sealed are provided at both ends of a main tube
68
made of transparent ceramics, and that the disk
64
a
further is provided with a slender ceramic tube
63
c
for the auxiliary electrode.
However, those types of discharge lamps have had following problems.
In the high-pressure metal vapor discharge lamp including the conventional quartz discharge tube as shown in
FIG. 9
, the sealing portions of the discharge tube are sealed by crushing during its manufacture, resulting in varying shapes. This shape variation has caused variation in lamp characteristics.
When the sealing portions are large, thermal loss from a discharge space of the discharge tube increases, making it difficult to obtain a sufficient efficiency and a high color rendition. Thus, it is necessary to reduce the size of the sealing portions as much as possible. However, in the quartz discharge tube, since it is necessary to seal the metal foil
41
on the main electrode side and the metal foil
45
on the auxiliary electrode side so as to space them away at a certain distance and prevent their contact, the size reduction of the sealing portion
37
has been difficult.
Also, in this type of high-pressure metal vapor discharge lamp, a Ne—Ar mixed gas is used as a starting gas for the purpose of lowering a starting voltage at discharge start-up. However, since Ne permeates the quartz as a discharge tube material, a mixed gas containing Ne needs to be sealed in the outer tube
2
so as to prevent this permeation. On the other hand, when the gas is sealed in the outer tube
2
, the thermal loss from the discharge tube
34
increases. Accordingly, in order to obtain sufficient characteristics, it is necessary to tolerate a deterioration of lifetime characteristics to a certain degree and increase a tube-wall load of the lamp. Such deterioration of lifetime characteristics is caused by a reaction between quartz in a wall portion of the discharge tube and a metal halide that has been sealed. Thus, it has been desired that such reaction between the quartz as the discharge tube material and the sealed metal halide is suppressed.
On the other hand, in the lamp disclosed in JP 62-150646 A using ceramics for the discharge tube, variation in the shape of the discharge tube can be suppressed, thus making it possible to improve quality regardless of the presence or absence of the gas in the outer tube. However, since an electrically conductive cermet
56
having the auxiliary electrode
54
is sealed air-tight with a sealing material
57
in a portion reaching a relatively high temperature during the lamp operation, leaks in the discharge tube during the operation or the reaction between the sealing material and enclosed metals are inevitable. Especially, in metal halide lamps using metal halide as a discharge metal, a violent reaction occurs.
In the lamp disclosed in JP 10-106491 A in which the electrode lead-in members are sealed in the slender ceramic tubes, the reaction between the sealing material and the enclosed metals can be avoided. However, when attempting to obtain a reliable mechanical strength of the disk
64
a,
it is difficult to reduce the distance between a main electrode
65
a
and an auxiliary electrode
66
and the shape of end portions of the discharge tube becomes limited. Consequently, it is difficult to design the discharge tube for the purpose of obtaining desired lamp characteristics.
DISCLOSURE OF INVENTION
The present invention was made in order to solve the problems described above, and it is an object of the present invention to provide a high-pressure metal vapor discharge lamp that prevents the occurrence of variations in characteristics caused by shape variation of a discharge tube as in a quartz discharge tube, achieves highly efficient and stable lifetime characteristics independent of the presence or absence and the composition of a gas in an outer tube, suppresses leaks during a lamp operation and characteristic changes caused by a reaction between a sealing material and an enclosed material, has stable lamp starting characteristics, and allows a free design of the discharge tube.
A high-pressure metal vapor discharge lamp of the present invention includes an outer tube sealed air-tight by a stem, and a discharge tube of transparent ceramic in which mercury, a rare gas and a discharge metal are sealed, the discharge tube being inside the outer tube. The discharge tube includes a main tube, a pair of slender tubes disposed at both ends of the main tube, at least a pair of main electrodes located in the main tube and at least an auxiliary electrode located in the main tube. The pair of main electrodes are connected to electrode lead-in members that are sealed in the slender tubes with a sealing material, the auxiliary electrode is connected to an auxili
Higashi Masanori
Nakayama Shiki
Nishiura Yoshiharu
Nohara Hiroshi
Oda Shigefumi
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Thuy Vinh
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