Electric lamp and discharge devices – With gas or vapor – With particular gas or vapor
Reexamination Certificate
1998-11-12
2001-04-03
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
With particular gas or vapor
C313S113000, C313S639000, C313S642000, C313S571000
Reexamination Certificate
active
06211616
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high pressure discharge lamp for use in general lighting fittings and optical apparatuses etc., and to a lighting optical apparatus comprising the high pressure discharge lamp and a reflecting mirror which are integrated into one unit, and to an image display system comprising the lighting optical apparatus and an image forming device.
BACKGROUND OF THE INVENTION
Conventionally, a lighting optical apparatus, which is used as a light supply in an image display system used in a liquid crystal projector or the like, usually comprises a light source and a reflecting mirror, which are integrated into one unit. Examples of the light source include halogen lamps, metal halide lamps, xenon lamps, extra-high pressure mercury lamps, and the like.
Recently, because of its good efficiency, high luminance, good balance of red, blue and green in the emitted light, long lifetime, and others, an extra-high pressure mercury lamp having a short electrode spacing, that is, with a short arc, which is dose to a point light source, has been used as a light source for a lighting optical apparatus.
Previously, this type of lighting optical apparatus as shown in
FIG. 8
, which comprises a high pressure discharge lamp, e.g. an extra-high pressure mercury lamp
17
, and a concave reflecting mirror
9
having a paraboloidal or ellipsoidal reflection surface (hereinafter referred to as the reflecting mirror
9
) integrated into one unit, has been used.
The light radiated from the extra-high pressure mercury lamp
17
is reflected by the reflecting mirror
9
and then it is radiated forward. If such a lighting optical apparatus is combined with an image display system with a condenser lens or an image forming device such as a liquid crystal panel, the light radiated forward is led into the condenser lens with a determined area, or into the image forming device such as a liquid panel in the image display system.
If the light reflected forward by the reflecting mirror
9
is parallel rays, the condensing efficiency becomes high. Thus, the light source is preferably a point light source. Therefore, an extra-high pressure mercury lamp having a short electrode spacing, i.e. with a short arc, which enables a point light source, may be used.
As an example of a conventional extra-high mercury lamp,
FIG. 8
illustrates the extra-high pressure mercury lamp
17
which comprises a luminous vessel
17
a
containing a pair of electrodes therein, and sealing parts
17
b
connected to each end of the luminous vessel
17
a
. An installation body as described below is sealed in each of the sealing parts
17
b
. The installation body comprises an electrode
18
comprising an electrode rod
18
b
and a coil
18
a
connected to the top end of the rod
18
b
, a metallic foil
5
comprising molybdenum whose one end is connected to the bottom end of the rod
18
b
, and an external lead wire
6
whose one end is connected to the other end of the metallic foil
5
. The installation body is sealed in the sealing part
17
b
in such a way that the electrode
18
is located in the luminous vessel
17
a.
One external lead wire (not shown) is electrically connected to the base
7
, and the other external lead wire
6
is connected to a power-supplying wire (not shown).
The luminous vessel
17
a
is filled with mercury as a light-emitting metal and rare gases, e.g. argon. The extra-high pressure mercury lamp
17
is attached to and integrated with the reflecting mirror
9
. The reflecting mirror
9
is made of a material selected from the group consisting of glass, metals and ceramic, and also has a reflecting surface comprising a deposited film of TiO
2
—SiO
2
and the like with excellent reflection property on the inner surface of the concave mirror. A front light-projecting portion of the reflecting mirror
9
, i.e. the opening portion, has a diameter of about 50 to 120 mm. The mirror
9
is further provided with a cylindrical support
10
at the back portion thereof. A base
7
of the extra-high pressure mercury lamp
17
is fixed to the cylindrical support
10
with an adhesive
11
, e.g. an insulating cement. Thereby, the extra-high pressure mercury lamp
17
is attached to the reflecting mirror
9
in such a way that the axis of the lamp corresponds approximately to the center of the reflecting mirror
9
. Furthermore, a lead-in hole (not shown) is formed through the reflecting mirror
9
, and above-mentioned power-supplying wire penetrates through the hole and is lead into the back side of the reflecting mirror
9
. In the case of power consumption at 80 to 150 W, such a conventional extra-high mercury lamp
17
has an electrode spacing as short as 1.0 to 2.0 mm, and is usually lighted up by a high-frequency alternating current power source at 125 to 400 Hz.
When such a discharge lamp with a short arc and a high luminance is lighted, the temperature at the end of the electrodes becomes very high, so that tungsten used as a material of the electrodes is scattered and adheres to the inner wall of the discharge tube. Thus, blackening of the discharge tube occurs within several tens of hours. In order to inhibit such blackening of the discharge tube, a method of filling a halogen gas in the discharge tube, so as to prevent blackening of the tube by utilizing a reaction called halogen cycle, has been proposed (Japanese Published Unexamined Patent Application (Tokkai) No. HEI 2-148561). The extra-high pressure mercury lamp as proposed in this publication is filled with more than 0.2 mg/mm
3
of mercury, and is also filled with at least one halogen selected from the group consisting of Cl, Br and I in an amount of 10
−6
to 10
−4
&mgr;mol/mm
3
.
However, in such a lamp, the pressure in the discharge tube during operation exceeds 2.0×10
7
Pa (200 bars), so that even a little blackening of the discharge tube can cause deformation of the tube, which may result in bursting of the discharge tube. Furthermore, residual impurity gases remained in the discharge tube, and impurity gases discharged from the electrodes and the quartz glass, which is used as a material of the discharge tube, inhibit the halogen cycle, resulting in shortening the lifetime of the lamp.
Thus, although such a conventional high pressure discharge lamp with a short arc and a high luminance has excellent initial properties, it has a disadvantage with respect to the lifetime of the lamp.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high pressure discharge lamp with a long lifetime, a lighting optical apparatus having such a high pressure discharge lamp as a light source, and an image display system using the lighting optical apparatus, by optimizing the amount of mercury filled and the halogen gas concentration in the discharge tube, and further by inhibiting generation of residual gases in the discharge tube and unnecessary gases which are generated during lighting.
In order to achieve the above-mentioned object, the high pressure discharge lamp of the present invention is provided with a discharge tube which contains a pair of electrodes therein and is filled with mercury, an inert gas and a halogen gas, the amount of the mercury filled being 0.12 to 0.35 mg/mm
3
, the halogen gas being at least one gas selected from the group consisting of Cl, Br and I, and being present in the range of 10
−7
to 10
−2
&mgr;mol/mm
3
, and the electrodes mainly being composed of tungsten, wherein the tungsten as a material of the electrodes contains not more than 12 ppm of potassium oxide (K
2
O). Accordingly, blackening of the discharge tube due to potassium oxide contained in the tungsten, and decrease in illumination maintenance can be prevented, so that a high pressure discharge lamp with a long lifetime can be obtained. The content of the potassium oxide (K
2
O) in the tungsten may be any amount in the range of not more than 12 ppm, but it is preferably 0 ppm to not more than 8 ppm, particularly preferably 0 ppm to not more than 5 ppm.
In the high pressure
Kitahara Yoshiki
Takeuti Nobuyosi
Tsutsumi Takeharu
Matsushita Electronics Corporation
Merchant & Gould P.C.
Patel Nimeshkumar D.
Williams Joseph
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