JPH04292847A - Metal halide lamp - Google Patents

Abstract

PURPOSE:To improve the uniformity of brightness and color of a light receiving surface by roughening at least a part of the inner surface of a transparent light emitting tube like ground glass. CONSTITUTION:The inner surface 2 of the quartz glass light emitting tube of a metal halide lamp is subjected to a frosting process. A tungsten electrode 1 is provided in the lamp, and the predetermined amount of argon, mercury and metal iodide is sealed therein as starting rare gas. As a result, a distance between an arc and the frosted surface 2 is shortened by an amount corresponding to the wall thickness of the light emitting tube, compared with the case of frosting the external surface 3 of the light emitting tube, thereby improving apparent brightness. According to this construction, brightness and color uniformity can be easily obtained, while luminous brightness is being kept high.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal halide lamp used for general lighting, optical equipment, etc.

0002

[Prior Art] In metal halide lamps, the brightness of the arc has a distribution both in the length direction of the arc and in the radial direction centered on the arc axis, and is particularly distributed in the area called the arc spot near the electrode tip. The brightness is high and the brightness distribution within the discharge space is non-uniform.

Furthermore, during lighting, mercury mainly emits light near the central axis of the arc, and around this mercury, the metal sealed as a halide emits a unique spectrum. (For example, Dy, Tl, Sc, In) In addition, metal halide molecules (DyI, etc.) may emit light in areas closer to the glass tube wall and at a lower temperature near the arc. Therefore, the brightness and spectral characteristics differ between the center and the periphery of the arc.

Now, in optical systems such as OHP projectors, liquid crystal projectors, etc., in which the light emitted from the light source is focused using a reflecting mirror, and the image of the OHP slide or liquid crystal panel is enlarged and projected using a lens system, the light source is small and the brightness,
It is required that both color (spectral distribution) be uniform.

When a metal halide lamp is used as a light source for such a projector, the above-mentioned non-uniformity of brightness and spectral characteristics within the arc poses a serious problem. That is, the central part of the light-receiving surface corresponding to the central axis of the arc is bright and has an excess of green and lack of red due to the dominant mercury emission, while the peripheral part of the light-receiving surface is dark and has an excess of red due to the luminescence of metal atoms and molecules. Conventionally, to solve this problem, the outer surface of the arc tube was made translucent (frosted glass) by sandblasting, etc.
A known method is to improve the brightness of the arc and the non-uniformity of the spectral characteristics.

[0006]

It is known that in metal halide lamps, the quartz glass which is the material of the arc tube reacts with the filler material, and the quartz glass erodes over the life of the lamp. Furthermore, while the lamp is lit, the inside of the arc tube is under high pressure of more than 10 atmospheres. Therefore, in consideration of safety and service life, the thickness of quartz glass is often set to about 1 to 2 mm. In the optical device, the brightness of the light-receiving surface is determined by the apparent brightness of the light emitter, but when the outer surface of the arc tube is frosted using the conventional method, the distance between the arc and the frosted surface is long as a result of the use of thick quartz glass. The brightness of the light emitter decreases significantly. As a result, the light utilization efficiency decreases, and even if the brightness and color uniformity of the light-receiving surface improves, the entire light-receiving surface becomes dark.

[0007] Therefore, the balance between the brightness of the entire light-receiving surface, the brightness of the light-receiving surface, and the uniformity of color is adjusted by the degree of frosting, that is, the transparency of the quartz glass. However, since the distance from the arc to the frosted surface is long, slight differences in the degree of frosting or unevenness in processing will cause large variations in the brightness and color of the light-receiving surface.

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal halide lamp which can solve the above-mentioned problems and improve the brightness and color uniformity of the light-receiving surface without significantly reducing the light collection efficiency.

[0009]

[Means for Solving the Problems] In order to achieve this object, the present invention provides a quartz glass arc tube with an uneven structure on the inner surface like ground glass.

0010

[Operation] The present invention frosts the inner surface of the quartz glass arc tube by sandblasting or acid etching, so the frosted surface is placed closer to the luminous body than in the conventional method of frosting the outer surface of the arc tube. can be placed. In other words, the distance from the arc to the frosted surface is shortened by the thickness of the arc tube, and the drop in apparent brightness can be improved compared to when the outer surface is frosted. Therefore, it is possible to easily obtain uniformity in brightness and color while keeping the brightness of the light emitter high. It can be easily inferred that the above effect is effective not only by sandblasting or acid etching, but also by methods such as fixing a thin film with unevenness or fine powder to the inner surface of the arc tube. .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. (FIG. 1) is a schematic cross-sectional view of a metal halide lamp arc tube made of quartz glass, the inner surface of which has been frosted. The lamp is filled with predetermined amounts of argon, mercury, and metal iodide as starting rare gases. The arc length is 7 mm. In the figure, 1 is a tungsten electrode hermetically sealed via a molybdenum foil, 2 is a frosted inner surface of the arc tube, 3 is an outer surface of the arc tube, and 4 is the central axis of the arc.

First, a simple experiment was conducted to investigate the effect of the distance from the light source to the frost surface on the apparent luminance of the light emitter. A light source 5 and a frosted glass plate 6 whose thickness can be ignored are arranged as shown in FIG. Measured by. The results are shown in (Figure 3).

[0013] In this experiment, it was found that the luminance of the light emitter decreases approximately in inverse proportion to the square of the distance from the light source to the frost surface. (Fig. 1), when the inner surface of the arc tube was frosted, the brightness was 1.7 times higher than that on the outer surface. This is because even if the frost density is the same, the shorter the distance between the arc and the frost surface, the smaller the apparent size of the light emitter.

(FIG. 4) shows a projector optical system incorporating the metal halide lamp of (FIG. 1), in which 9 is an arc tube, 10 is a reflecting mirror, 11 is a condensing/projection lens system, and 12 is a light receiving surface.

In this projector optical system, the lamp is turned on at 90V and 1.7A, and the center of the light receiving surface and the 0.
The illuminance and spectral distribution of points at nine angles of view were measured. The results are shown in Table 1, together with the cases where the outer surface of the arc tube was frosted and the cases where no frosting was applied at all. The illuminance at each point in the case of the frosted inner surface and the frosted outer surface is expressed as a relative ratio with respect to the center of the light-receiving surface in the case of no frosting. In addition, the spectral distribution is evaluated by color temperature,
It is expressed as a difference from the color temperature at the center of the light-receiving surface when there is no frost, based on the color temperature at each point when the inner surface is frosted and the outer surface is frosted.

[0016]

[Table 1]

As is clear from Table 1, when the inner surface of the arc tube is frosted according to the present invention, the reduction in brightness at the center of the light-receiving surface can be improved compared to when the outer surface is frosted, and the amount of peripheral light (0.9 40% of the center (illuminance at the angle of view point)
I was able to get more than that. In addition, the difference in color temperature between the center of the light-receiving surface and the periphery has been improved from 5000K without frosting and 200K with frosting on the outer surface to 150K, and the frost on the inner surface has significantly reduced the brightness drop at the center of the light-receiving surface. It can be said that the brightness and color uniformity were improved without the need for

In general, it is difficult to achieve uniform frosting by sandblasting, but according to the present invention, even if there is a difference in the degree of frosting depending on the location on the inner surface of the arc tube, the arc and the frosted surface are close to each other, and the frosted surface and Because the reflecting mirror is farther away than before, it is less likely to be reflected in variations in brightness on the light receiving surface. This facilitates the control of the frosting process in production, which is an advantage of the present invention. In addition, as a result of frosting the inner surface of the arc tube, some of the light emitted from the arc is diffusely reflected and returns to the inside of the arc tube. Improves heat retention. As a result, the vapor pressure of the encapsulated metal halide in the metal halide lamp increases, making it easier to obtain light emission unique to the encapsulated metal.

Next, the relationship with the arc length of the metal halide lamp will be described. Generally, the life of a metal halide lamp varies depending on the arc length. For example 15
In the case of a 0W metal halide lamp, if the arc length is 3 mm, the life is 500 hours, but if it is 5 mm, the life is 1000 hours.
It's time. Further, when the arc length is 10 mm, the life is 2000 hours, and when it is 20 mm, it is 5000 hours. On the other hand, in the projector optical system that combines a metal halide lamp and a reflecting mirror, the lamp is required to be close to a point light source, that is, to have a short arc length and high brightness in terms of light collection efficiency. If the arc length is long, the luminous body becomes large and the brightness decreases. Therefore, the optimum range of arc length is determined by life and brightness. (Fig. 4) A lamp with a frosted inner surface or a frosted outer surface with only the arc length changed is placed in the projector optical system,
The illuminance at the center of the light-receiving surface was evaluated in the same manner as described above, and expressed as a relative value with respect to the case where the arc length was 7 mm and the inner surface was frosted. It is shown in Table 2 along with the lifespan.

[0020]

[Table 2]

From the results shown in Table 2, when the arc length exceeds 10 mm, the luminous body becomes large and the level of brightness itself becomes low, so the effect of the inner surface frost is not so great. The inner surface frost is more effective than the outer surface frost when the arc length is 10 mm or less. arc length is 3
If the diameter is less than mm, the life time will be less than 500 hours, and the range of application will be extremely limited, making it impractical. Combining these results and considering the lifespan, the present invention is particularly effective when the arc length is 3 mm or more and 10 mm or less.

[0022]

As described above, according to the present invention, by forming the inner surface of the transparent arc tube of a metal halide lamp into an uneven structure by frosting or the like, the luminance inside the luminous body can be increased without reducing the apparent luminance of the luminous body. , it is possible to make the spectral distribution uniform, and when used as a light source for a projector, it is possible to achieve high light-receiving surface brightness and at the same time to improve the uniformity of brightness and color within the light-receiving surface.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a quartz glass arc tube whose inner surface is frosted according to an embodiment of the present invention.

[Figure 2] Configuration diagram of the device used in the experiment

[Figure 3] Graph showing the relationship between the distance from the arc to the frost surface and the brightness

FIG. 4 is a configuration diagram of a projector optical system incorporating a metal halide lamp according to the present invention.

[Explanation of symbols]

1 Tungsten electrode 2 Inner surface of arc tube 3 Outer surface of arc tube 4 Arc center axis 5 Light source 6. Frosted glass plate 7 Luminance meter 8 Distance from light source to frost surface 9 Arc tube 10 Reflector 11 Condensing/projection lens system 12 Photo-receiving surface

Claims (2)

[Claims] 1. A metal halide lamp characterized in that at least a portion of the inner surface of the transparent arc tube has a frosted glass-like uneven structure. 2. A metal halide lamp having an arc length of 3 mm or more and 10 mm or less, in a transparent arc tube combined with a reflecting mirror, wherein at least a part of the inner surface of the arc tube has a frosted glass-like uneven structure.