Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
2000-03-07
2001-09-25
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S624000, C313S625000
Reexamination Certificate
active
06294870
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a high-pressure discharge lamp, a high-pressure discharge lamp device and a light source device, each one of which may be used in, for example, a liquid crystal projector.
BACKGROUND OF THE INVENTION
Nowadays, projection-type image display devices are rapidly becoming commonplace. Such a display device is often equipped with a high pressure discharge lamps as its light source. Among various high pressure discharge lamps, short-arc type high pressure discharge lamps that function virtually as point sources of light and are easy to arrange and control, are widely used as the light sources of liquid crystal projectors, which are becoming particularly popular these days. Typical examples of said short-arc type high pressure discharge lamps include xenon lamps and metal halide lamps.
A liquid crystal projector is an apparatus adapted to project images onto a screen by using a liquid crystal display panel and is capable of clearly projecting not only static images but also moving pictures. As liquid crystal projectors are capable of projecting various images based on signals representing the images regardless of whether the input signals are analog or digital, they are used as a tool for making presentations, a screen in a make-shift theater, or as the screen of a large-screen television, and their demands are expected to keep increasing in the future.
Compared with such inexpensive image display devices as CRT displays, liquid crystal projectors are very expensive. Therefore, efforts are being exerted to provide a less expensive liquid crystal projector by making it compact or otherwise reducing its production costs. Furthermore, as there is still room for further improvement in brightness, progress is being made to employ a special optical system.
As it is mentioned above, a high pressure discharge lamp is popularly used as a light source device for a liquid crystal projector, and what are now required of a high pressure discharge lamp are a reduced distance between the electrodes, a higher efficiency and a longer life span. In addition to these demands, ensured reliability and reduction of production costs, which is the present objective of the liquid crystal projector, are required of high pressure discharge lamps.
In most cases, a high pressure discharge lamp used in such an image display apparatus as mentioned above is installed in the apparatus in such a manner that it will be lit in the horizontal position. When a lamp is lit in the horizontal position, a convection current generated in the arc tube makes the temperature of the upper part of the inside of the arc tube higher than the other part, thereby making the temperature distribution in the entire arc tube nonuniform. In order to solve the problem of nonuniformity of temperature distribution, an air cooling device, such as a fan, is installed.
One of the important processes of producing a high pressure discharge lamp is the sealing process to form the inside of the arc tube into an airtight space. The sealing process is conducted by the pinch sealing method, which enables the quick and efficient processing. A portion sealed by the pinch sealing method can be maintained in a sufficiently airtight state having the ability to withstand the high internal pressure and ensures reliable functioning of the lamp in desired performance characteristics for a long period of time.
The arc tube has to be provided with two sealed portions: one each at the cathode side and the anode side. A metal foil conductor which is made of molybdenum and connected to the cathode is attached to one of the sealed portions, while another molybdenum metal foil conductor, which is connected to the anode, is attached to the other sealed portion. A lead wire made of molybdenum extends from each sealed portion to the outside of arc tube. Inside each sealed portion, the metal foil conductor and the lead wire are connected by welding. As the outside atmosphere enters the portion where they are welded, the welded portion is in a condition similar to that if it were exposed to fire. As a result, when it is in a high temperature environment for a long time, it is prone to oxidation and possible breakage. There is a demand for an effective means to solve this problem by maintaining the welded portions at a lower temperature.
This may be achieved by somehow reducing the heat conducted from the heat source or cooling the welded portion to limit increases of temperature. However, a cooling method is almost never employed, because noises produced by an air blower, which may be an air cooling fan or the like, make it difficult to attain the objective of reducing noises. Therefore, lamps produced these days usually employ a method which calls for increasing the length of either one of or each sealed portion in order to reduce the heat conducted from the source of heat generation.
FIG. 7
is a characteristic graph showing the relationship between distances from various points to the surface of the discharge space of the arc tube, which is the source of heat generation, and temperatures at said points. When the distance from the surface of the discharge space of the arc tube exceeds 30 mm, the temperature is in the permissible range to ensure that the sealed portion achieves the expected life expectancy.
However, in case the lamp is a small high pressure discharge lamp described above with the length of the portion to be sealed exceeding 30 mm, it is difficult to seal the target portion by the pinch sealing method. In other words, in case of a small high pressure discharge lamp, it is impossible to provide a sufficiently long distance from the center of the arc, which serves as the source of heat generation.
Accordingly, the first object of the present invention is to ensure that the sealed portion achieves the expected life expectancy and to provide a high pressure discharge lamp, a high pressure discharge lamp device and a light source device using said high pressure discharge lamp, wherein the lamp has sealed portions formed by the pinch sealing method, and wherein a sealed portion is maintained at a desired distance from the heat source.
As described above, an arc tube to be lit in the horizontal position may be provided with an air cooling device, such as an air blower, in order to make the temperature distribution uniform throughout the inside of the arc tube. However, installing an air cooling device not only presents the problem of noises but also presents another problem in that it may become impossible to obtain necessary luminescence characteristics if the arc tube is cooled excessively. In other words, control of the air cooling device is difficult. Although this problem may be overcome by lighting the arc tube in the vertical position, vertical lighting causes substantial increase of the temperature of the upper sealed portion and, therefore, tends to enhance oxidation of the metal foil sealed therein and makes the metal foil even easier to break.
Accordingly, the second object of the present invention is to ensure that the sealed portion achieves the expected life expectancy when the lamp is used in the vertical position and to provide a high pressure discharge lamp, a high pressure discharge lamp device and a light source device using said high pressure discharge lamp, wherein the possibility of breakage of a metal foil is reduced even if the lamp is used in the vertical position.
As it is mentioned above, floodlight illumination and image display devices are rapidly becoming commonplace over recent years, and high pressure discharge lamps are used as their light sources in most cases. Among various high pressure discharge lamps, short-arc type high pressure discharge lamps that function virtually as point sources of light and are easy to arrange and control, such as metal halide discharge lamps, are widely used as the light sources of liquid crystal projectors, which are becoming particularly popular these days in addition, using a metal halide discharge lamp as the light source of a vehicle headlight i
Kawashima Hiromichi
Nishizawa Makoto
Berck Ken A
Morrison Law Firm
Patel Nimeshkumar D.
Toshiba Lighting & Technology Corporation
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