Electric lamp and discharge devices – With magnetic device – With envelope
Reexamination Certificate
1998-07-28
2001-06-19
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With magnetic device
With envelope
C313S637000, C313S638000, C313S639000, C313S043000
Reexamination Certificate
active
06249078
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a microwave-excited discharge lamp which emits light by discharge under a microwave electromagnetic field.
Conventionally, in a liquid crystal projection display using a liquid crystal panel, an electrode discharge lamp including a metal halide lamp and a xenon lamp has been used as a light source. As is well known, in the light source of the liquid crystal projection display, a light output must be collimated through a lens for projection into the liquid crystal panel. Therefore, as the light source, it has been necessary to reduce the size of a light emitting part as much as possible in order to increase its light utilization. Furthermore, it has been required to retain the light output even when the size of the light emitting part is reduced. In existing electrode discharge lamps including the metal halide lamp, the size reduction of the light emitting part has been achieved by shortening a gap of electrodes thereof. However, in the case that the gap of the electrodes is shortened without reducing the light output, electric power applied to the electrodes inevitably becomes large in the electrode discharge lamp. As a result, the lifetime of the electrode discharge lamp has been extremely short (several thousand hours) compared with the lifetime required for a television monitor and the like. Various efforts have been made to date, but the electrode discharge lamp that can satisfy the brightness and lifetime requirements at the same time has not yet been developed or commercially implemented.
In recent years, an inherently long life electrodeless discharge lamp, which is free from electrode deterioration determining the above-mentioned lifetime of the electrode discharge lamp, has been attracting attention. One commercial implementation of the electrodeless discharge lamp is a microwave-excited discharge lamp which emits light by discharge under a microwave electromagnetic field formed by a microwave (in the 1 GHz to several tens of GHz band).
As a conventional microwave-excited discharge lamp, there is a description in IDW (International Display Workshop), 1996 version, pp. 435-438 (“Novel High Color Rendering Electrodeless HID Lamp Containing InX). This conventional microwave-excited discharge lamp uses a discharge tube with thickness about 1.5 mm and outer diameter 15, 20, 30, or 40 mm. Inside of the discharge tube is filled with argon (Ar) and an indium halide, namely, indium iodide (InI) or indium bromide (InBr).
When such conventional microwave-excited discharge lamp is used as the aforementioned light source instead of a short arc HID lamp, the discharge tube must be made smaller with its inner diameter reduced to about 3 mm to 8 mm. However, as is well known, in the microwave-excited discharge lamp, the smaller the discharge tube is made, the closer becomes the distance between the tube wall and the plasma discharge generated in the discharge tube, resulting in higher tube wall temperature. Accordingly, in the conventional microwave-excited discharge lamp, when the discharge tube is reduced in size, it has become necessary to cool the lamp in order to maintain stable operating condition, and it has also been necessary to control the lamp temperature with high accuracy.
It is known to seal mercury as a buffer gas within the discharge tube in order to maintain the stable operating condition. However, in the conventional microwave-excited discharge lamp, there is a problem of a low luminous efficacy when the amount of the buffer gas comprising mercury is increased. As a result, in the conventional microwave-excited discharge lamp, it is necessary that the amount of mercury to be sealed inside the discharge tube is extremely small. However, accurately sealing a very small amount of mercury into the discharge tube has been impracticable in mass production, though it may be possible in the laboratory. Therefore, it has been difficult to use the conventional microwave-excited discharge lamp as the aforementioned light source.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a microwave-excited discharge lamp that can solve the aforementioned problems in the conventional microwave-excited discharge lamp and can be configured with less cost and has a long life.
In order to achieve the above-mentioned object, a microwave-excited discharge lamp comprises:
a discharge tube, and
a rare gas, a mercury halide as a buffer material, and a metal halide as a luminous material sealed within the discharge tube.
With this construction, a microwave-excited discharge lamp can be obtained which is capable of being started easily even when a discharge tube is reduced in size, and which can readily provide more stable operating condition compared with the conventional microwave-excited discharge lamp. Furthermore, the microwave-excited discharge lamp can be used as a light source for a liquid crystal projection display, and it is easily possible to realize the microwave-excited discharge lamp having a small-size discharge tube that emits a variety of light colors.
In the microwave-excited discharge lamp of another aspect of the present invention, a discharge tube, and a rare gas, tin iodide as a buffer material, and a metal halide as a luminous material sealed within the discharge tube.
With this construction, a mercuryless microwave-excited discharge lamp can be achieved.
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A. Hochi et al., “Novel High Color Rendering Electrodeless HID Lamp Containing InX”,International Display Workshop(IDW), pp. 435-438, (1996) (No Month).
Akin Gump Strauss Hauer & Feld L.L.P.
Matsushita Electronics Corporation
Patel Ashok
Santiago Mariceli
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