JPH05290807A - Metal halide lamp - Google Patents

Abstract

PURPOSE:To make light emission uniform and enhance a light utilizing rate and a light condensing rate in the case of combination with a light condensing mirror by applying a frosting treatment onto an inner surface of a light emitting tube. CONSTITUTION:A frosting treatment 5 is applied onto the inner surface of a light emitting tube 1 by a chemical etching method or a sand blast method by the use of hydrofluoric acid. Metal halide, mercury and argon are enclosed in the light emitting tube 1. A molybdenum foil 3 is welded to the base of an electrode 2 so that the electrode 2 is airtightly sealed. A molybdenum lead 4 is connected to the molybdenum foil 3. Accordingly, light is emitted from the frosted surface of a lamp, and therefore, most of the light is emitted to the outside as diffusing light. Consequently, it is possible to reduce unevenness of luminance and color without deterioration of efficiency of the lamp. Moreover, a light utilizing rate and a light condensing rate can be enhanced owing to a small light emitting portion in the case of combination with a light condensing mirror.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a metal halide lamp used as a light source for illumination or image display by utilizing light emitted from discharge of metal vapor.

[0002]

2. Description of the Related Art The structure of a metal halide lamp (hereinafter simply referred to as a lamp) arc tube is described, for example, in P1 of the Lighting Handbook (Illumination Society of Japan, Ohmsha, 1987).
45-148. In addition, recently, metal halide lamps have been published by LS-90-5, P3
1-39 (February 1990), it has come to be used also as a light source for image display, for example, a liquid crystal projector.

However, the light emission of the above-mentioned prior art lamps uses the light emitted directly from the arc of the discharge. For this reason, strong light emission of the electrode bright spots, color differences due to the temperature distribution of the arc, etc. appear as they are, and there are brightness unevenness and color unevenness. In addition, in a metal halide lamp, there is a phenomenon that the enclosed halide reacts with the quartz glass of the arc tube during lighting and the inner surface of the arc tube becomes devitrified and becomes cloudy. When this devitrification and white turbidity occur, the arc becomes unclear, and the state of light emission changes greatly compared to the initial lighting, and there is a problem in using it as the light source of the above-mentioned unevenness and optical equipment.

To improve these problems, for example,
As disclosed in Japanese Patent Application Laid-Open No. 2-244089, it is known that the surface of a lamp arc tube is frosted before use. However, when a lamp having such a structure is used, the uniformity of light emission is improved, but since the light emitting portion becomes large, there is a problem in that the light collection rate decreases when incorporated in a light collecting mirror, and the screen becomes dark. there were.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce unevenness in brightness and color of a light source, improve the uniformity of light emission, and use the light source by incorporating it into a condenser mirror or the like like an optical device. In that case, it is also necessary to improve the light collection rate and obtain a bright screen.

[0006]

The above object is achieved by providing a frosted structure (the surface is satin and semi-transparent) on the inner surface of the arc tube.

[0007]

[Function] By frosting the inner surface of the arc tube, the light emission is not the light emitted directly from the arc of the discharge,
It changes to diffused light from the frosted surface. Therefore, the uneven brightness,
Color unevenness can be reduced. In addition, when the light source is incorporated into a condensing mirror or the like and used for condensing, it is desirable that the light source be as close to a point light source as possible. The size can be made small, and when used by being incorporated in a condenser mirror, the condensing rate can be improved and a bright screen can be obtained.

[0008]

1 is a partial sectional view of an arc tube showing an embodiment of a metal halide lamp according to the present invention. In the figure, reference numeral 1 denotes an arc tube made of quartz glass, and a pair of discharge electrodes 2 are provided at both ends of this arc tube. The arc tube 1 is filled with metal halides such as dysprosium iodide and neodymium iodide, mercury, and argon as a starting gas for several thousand Pa to tens of thousands Pa. A molybdenum foil 3 is welded to the base of the electrode 2 to hermetically seal the electrode 2, and a molybdenum lead wire 4 is connected to an end of the molybdenum foil 3.

Frost processing 5 is applied to the inner surface of the arc tube 1. Frost processing can be easily performed by chemical etching using hydrofluoric acid, sand blasting, or the like.

In the manufacture of the lamp, the step of frosting may be performed in advance before sealing the electrodes on both ends of the arc tube. During electrode sealing, the sealed portion is heated until the quartz glass softens. Therefore, the frost effect disappears at the electrode base portion due to softening due to heating, but it does not cause a problem because it does not affect the arc generation portion of the discharge.

According to the present invention, the light emitted from the lamp becomes the light emitted from the frosted surface (the inner surface of the arc tube 1) and almost all is emitted to the outside as diffused light, so that the lamp efficiency is hardly reduced. In addition, uneven brightness and uneven color can be reduced.

FIG. 2 shows the basic structure of a liquid crystal projector. The lamp 10 is installed at a substantially focal position of a condenser mirror 11 having a shape such as a paraboloid of revolution, and white light emitted from the lamp 10 is reflected by a dichroic mirror 12.
Color separation into three primary colors of red, blue and green. The color-separated red, blue, and green monochromatic lights are incident on the liquid crystal panel 15 corresponding to the respective colors, and the brightness is modulated according to the image signal to become monochromatic image lights. The red, blue, and green monochromatic image lights are combined again by the dichroic mirror 13, and the projection lens 16
You can obtain a full-color large-screen image by enlarging and projecting on the screen. Reference numeral 14 is a mirror provided to bend the optical axis.

When the metal halide lamp according to the present invention is used as the light source of the liquid crystal projector, the light emitted from the lamp 10 is diffused light shining on the inner surface of the arc tube, and therefore the arc of the discharge cannot be directly observed. Brightness unevenness and color unevenness are reduced. Therefore, a light source with good uniformity can be obtained, and good image display can be performed.

Further, in the conventional lamp in which the outer surface of the arc tube is frosted, the diameter of the light emitting portion is the outer diameter of the light emitting tube. In the present invention, the diameter of the light emitting portion is the same as the inner diameter of the light emitting tube. Normal quartz glass tube has a wall thickness of 1 to 1.5 mm
By frosting the inside of the arc tube, the size of the light emitting portion can be reduced by 2 to 3 mm (about 20% depending on the tube diameter). When used in combination with a condensing mirror, it is desirable that the light source is as small as possible, and according to the present embodiment, the condensing ratio can be improved, the light utilization ratio can be improved, and a bright screen can be obtained.

Further, the frosted surface has fine irregularities, and if dirt adheres to this surface, it is difficult to remove it,
Due to this dirt, the luminous flux may be reduced or the quartz glass may be deteriorated to damage the lamp. In this embodiment, since the inner surface of the arc tube is frosted, the outer surface of the arc tube is smooth and hard to stain, and there is an advantage that such a problem does not occur.

[0016]

According to the present invention, when the inner surface of the arc tube of the metal halide lamp is frosted (the surface is satin and semi-transparent), it uniformly emits light, and when it is incorporated in a condenser mirror, Since the light emitting portion is small, the light collection rate is good, and good characteristics can be obtained when used as a light source for optical equipment. Further, since the surface of the arc tube is smooth, stains are unlikely to occur, and there is an advantage that characteristic changes such as reduction of luminous flux and deterioration of quartz glass are small.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a metal halide lamp arc tube according to an embodiment of the present invention.

FIG. 2 is a system diagram showing a basic configuration of a liquid crystal projector.

[Explanation of symbols]

1 ... Arc tube, 2 ... Electrode, 3 ... Molybdenum foil, 4 ... Lead wire, 5 ... Frost processing.

Claims (2)

[Claims] 1. A metal halide lamp having at least a pair of electrodes, wherein a rare gas for starting, a metal halide, and mercury are enclosed in an arc tube, wherein an inner surface of the arc tube has a frost structure. And a metal halide lamp. 2. The magnifying projection device according to claim 1, wherein a metal halide lamp using the arc tube is used as a light source.