JPH06310095A - Metal halide lamp and light projection apparatus using same for its light source - Google Patents

Abstract

PURPOSE:To provide a metal halide lamp of such structure that the blackening of a luminous tube can be prevented to keep the lumen maintenance factor thereof at a high level while the breaking of each electrode at its early stage of operation can be prevented to substantially improve the life characteristic of the tube, and a light projection apparatus using the lamp for its light source. CONSTITUTION:A metal halide lamp has electrodes 21a, 21b sealingly installed in its luminous tube 20, and has mercury, a rare-earth metal halide and a rare gas respectively sealed in the luminous tube 20. The proportion of bromine contained in a halogen sealed in the tube 20 to the halogen by the number of atoms is set to 60% to 90%, the voltage of a DC component is applied between the electrodes 21a, 21b to light the lamp by DC electricity, and the anode 21a is formed in large size over the size of the cathode 21b. The lamp thus has a large quantity of highly reactive bromine as the halogen sealed in the tube 20 so that the blackening of the tube 20 can be prevented, and it also has the tube 20 lit by DC electricity so that bromine of high electro-negativity can be attracted to the side of the anode 21a in large shape to prevent breaking the thick anode 21a at its early stage of operation.

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 and a light projecting device which uses the lamp as a light source and reflects light emitted from the light source by a reflector.

[0002]

2. Description of the Related Art A light projector such as a color liquid crystal projector is composed of a lamp which is a light source and a reflector which reflects light emitted from the lamp. As this type of lamp, a short arc metal halide lamp having an electrode distance of 15 mm or less is used.

The basic principle of the color liquid crystal projector will be described with reference to FIG.
A light projecting device 50 including a lamp 1 which is a light source and a reflector 2 which reflects light emitted from the light source is provided, and a condenser lens 3 which collects the reflected light reflected by the reflector 2 is provided. ing.

The light radiated forward is reflected by a dichroic mirror (wavelength selective reflecting mirror) 4 that reflects blue light, and this blue light is reflected by a mirror 5 to a liquid crystal panel (LCD) 6. The image on the liquid crystal panel 6 is illuminated with blue light and projected on the screen 10 through the other dichroic mirrors 7 and 8 and the projection lens 9.

Of the light projected from the condenser lens 3, the red and green lights pass through the dichroic mirror 4 which reflects the blue light, and the red light is reflected by the other dichroic mirror 11. LCD panel 1
2, the image on the liquid crystal panel 12 is colored red, and the red image is reflected by the dichroic mirror 7 and transmitted through the other dichroic mirrors 8 and the projection lens 9
The image is projected on the screen 10 via.

Further, the green light transmitted through the dichroic mirror 11 for reflecting the red light irradiates the liquid crystal panel 13 to color the image on the liquid crystal panel 13 green, and the green image is reflected by the mirror 14 and the dichroic mirror. It is reflected by 8 and projected on the screen 10 via the projection lens 9.

Therefore, by controlling the images of the three liquid crystal panels 6, 12 and 13, the images of three colors are superimposed and projected on the screen 10, and the color images are displayed.

As a light source for such a color liquid crystal projector, a large amount of light can be obtained in spite of the shape of a point light source and low power, and red, blue and green components are efficiently radiated, and a mirror or Even when used in combination with an optical system such as a lens, a lamp that can send abundant three primary colors of light to the necessary area and that can satisfy the conditions such as less heat generation is required. . The short arc metal halide lamp described above is suitable as a lamp satisfying such conditions.

A conventional light projecting device 50 which uses a short arc metal halide lamp as a light source and combines the short arc metal halide lamp 1 and a reflector 2 will be described with reference to FIG.

In FIG. 4, reference numeral 20 denotes an arc tube of the short arc metal halide lamp 1. This arc tube 20 is made of quartz glass and has electrodes 21 and 21 sealed at both ends thereof, and the pair of electrodes 21 and 21 is sealed. It is connected to the metal foil conductors 23 and 23 sealed to the stoppers 22 and 22. One of the metal foil conductors 23 is electrically connected to a cap 24 attached to the end portion via an external lead wire (not shown),
The other metal foil conductor 23 is connected to the external lead wire 25. The arc tube 20 is filled with mercury as a buffer metal, a metal halide as a light emitting metal, and a rare gas such as argon.

Such a lamp 1 is attached to a reflector 2. The reflector 2 is made of glass or metal and has a TiO ₂ -excellent reflective property on the inner surface of the rotating curved surface.
It has a reflecting surface 31 made of a vapor deposition film such as SiO ₂ . The front light-projecting portion of the reflector 2, that is, the opening portion is formed with an opening diameter of about 90 to 130 mm, and the support cylinder portion 32 is provided on the top of the back portion. This support tube portion 32
The base 24 portion of the lamp 1 is fixedly attached to the inside by an adhesive 33 such as insulating cement. As a result, the lamp 1 is attached to the reflector 2 such that the lamp axis O ₁ -O ₁ is substantially aligned with the central axis of the reflector 2, that is, the optical axis O ₂ -O ₂ . The reflector 2 has an introduction hole 3
4 is formed, and the external lead wire 25 of the lamp 1 is penetrated through the introduction hole 34 and is guided to the rear surface side of the reflector 2.

In such a lamp 1, the arc length, that is, the distance L between the electrodes is 15 mm or less, specifically 4 to 7 mm, and 150 W to 250 W of electric power is supplied during lighting, for example, 50 from a commercial power source. By supplying an AC cycle of -60 Hz or a high frequency of 250 to 400 Hz from a high frequency power source 50 converted by an electronic ballast,
It is used under a large load condition such that the tube wall load Z (a value obtained by dividing the input power W by the inner surface area Scm ² of the arc tube, Z = W / S) is 40 to 100 W / cm ² . Note that 250 to 40
Lighting the lamp with a high frequency of 0 Hz has the advantage of preventing the pulsation of the light output.
It is often turned on by a high frequency AC power supply of 400 Hz.

The short arc metal halide lamp 1 of this type has a high luminous efficiency, a high color temperature and a correlated color temperature of 6000 K or more as a metal halide enclosed in the arc tube 20. Rare earth metals such as dysprosium Dy and neodymium Nd are mainly used in order to obtain so-called high efficiency and high color rendering properties, which have an emission spectrum over all visible light and are suitable for efficiently emitting the three primary colors of light. . Further, in order to enhance the emission spectrum of a specific region and further improve the color rendering properties, an alkali metal such as cesium Cs and lithium Li and a halide of a metal such as indium In, thallium Tl and tin Sn are used. .

However, as described above, 40 to 100
The short arc metal halide lamp used with a high load of W / cm ^{2 on the} wall causes blackening of the wall of the arc tube early as the lighting time elapses. Such blackening causes devitrification of the quartz glass, lowers the luminous flux maintenance factor, and significantly shortens the lamp life.

When the cause of blackening of the arc tube was investigated, it was found that the presence of iodine encapsulated as halogen had a great influence. That is, this type of lamp mainly uses iodine I and bromine Br as halogens. When iodine I is used as the halogen, iodine is easily combined with a rare earth metal that enhances the color rendering property, which is effective in increasing the color temperature of the lamp, and the color rendering property is improved by the action of the luminescent metal that enhances the color rendering property. . However, when only iodine I is used as the halogen, premature blackening of the tube wall is likely to occur.

That is, this type of metal halide lamp has an arc temperature of 40 in the vicinity of the center of the arc in the arc tube.
The temperature becomes as high as about 00 to 6000 ° C., and the enclosed metal halide is decomposed by the high temperature at the center of the arc due to the rare earth metal and halogen, and further ionized. The rare earth metal and halogen thus decomposed are originally recombined in the vicinity of the wall of the tube to become a metal halide, which moves to a high temperature portion and is decomposed to repeat a so-called halogen cycle.

However, for example, dysprosium iodide Dy
In the case of a lamp in which I is encapsulated as a luminescent metal, free iodine I decomposed with dysprosium Dy at the high temperature portion in the center of the arc reacts with quartz (SiO ₂ ) of the arc tube at the tube wall to produce SiI ₄ . Such a reaction is more likely to occur as the tube wall load is higher and the tube wall temperature of the arc tube is higher, and thus is particularly likely to occur particularly in the above short arc metal halide lamp. When SiI ₄ is generated, it adheres to the tip of the electrode and forms a low melting point alloy of tungsten W and silicon Si with the tungsten W forming the electrode. Since this alloy has a low melting point, it is subjected to electron impact and scattered from the tip of the electrode, and the scattered low melting point metal adheres to the inner surface of the valve, which causes the valve to blacken.

On the other hand, when bromine Br is enclosed as halogen instead of iodine I, bromine Br is iodine I.
There is a property that it is superior in reactivity compared to. Therefore, bromine Br
Is a low melting point alloy of tungsten W and silicon Si adhering to the wall of the tube and is combined with tungsten W to form tungsten W.
Has a strong effect of returning to the electrode. That is, bromine Br has a higher recovery performance for the tungsten W adhering to the pipe wall than iodine I, and is therefore effective for cleaning the pipe wall.

Further, since bromine Br has higher reactivity than iodine I, it is easy to bond with free rare earth metals such as dysprosium Dy decomposed in the high temperature portion of the arc center, and the free rare earth metals adhere to the tube wall. It also has the effect of reducing the strain.

From the above, when bromine Br is used as the halogen, it is friendly to prevent blackening of the tube wall, and therefore the luminous flux maintenance factor can be improved. However, bromine Br is excellent in the action of returning to the high temperature portion of the electrode tip by combining with the tungsten W of the tube wall as described above, but on the other hand, bromine Br is highly reactive, and therefore the electrode Tungsten W and S at the base of the shaft
It also has a function of reacting W formed between iI ₄ and tungsten W of the low melting point alloy of Si, and carrying this tungsten W to the high temperature electrode tip. Therefore, tungsten W
Is transferred from the root of the electrode shaft with a low temperature to the high temperature part of the electrode tip and is deposited on the electrode tip.As a result, the electrode becomes thin at the base of the electrode shaft and the electrode shaft breaks early. There is.

[0021]

In view of the above, an object of the present invention is to use halogen as a halogen in order to improve the luminous flux maintenance factor due to blackening of the tube wall in the case of the conventional short arc metal halide lamp having a high tube wall load. When bromine Br is used, there is a problem that the electrode root is broken early.

Therefore, an object of the present invention is to prevent the blackening of the arc tube to maintain a high luminous flux maintenance factor and prevent the electrode from prematurely being broken, which in turn makes it possible to greatly improve the life characteristics. It is intended to provide a lamp and a light projecting device using the lamp as a light source.

[0023]

According to a first aspect of the present invention, electrodes are sealed at both ends of an arc tube, and mercury, at least a rare earth metal halide, and a rare gas are enclosed in the arc tube. In the lamp, the proportion of bromine in the halogen enclosed in the arc tube is in the range of 60 to 90% in atomic number ratio, and a DC component voltage is applied to the electrodes to light the lamp with DC.
It is characterized in that the electrode serving as an anode during lighting is formed larger than the electrode serving as a cathode.

The invention according to claim 2 is characterized in that halogen other than bromine in the halogen sealed in the arc tube contains iodine, and the proportion of this iodine is 90% or more in terms of the number of atoms.

According to the invention of claim 3, the metal halide is
It is characterized by containing at least one of halides of dysprosium, indium and thallium. The invention according to claim 4 is characterized in that the metal halide contains at least one kind of halides of dysprosium, neodymium and cesium.

A fifth aspect of the invention is characterized in that the lamp is a short arc type metal halide lamp having an electrode distance L of both electrodes of 15 mm or less. The invention of claim 6 is
A light projection device comprising: the metal halide lamp according to any one of claims 1 to 5; and a reflector that reflects light emitted from the lamp.

According to a seventh aspect of the present invention, the metal halide lamp is horizontally lit, the lamp axis is arranged along the optical axis of the reflector, and the electrode serving as the cathode during lighting is arranged on the front light projecting portion side of the reflector. It is a light projecting device.

[0028]

In the short arc metal halide lamp according to claim 1, since the amount of bromine Br enclosed as halogen is large, the tungsten W having bromine Br attached to the tube wall has a reactivity higher than that of iodine I. Has a strong effect of returning the tungsten W to the electrode by combining with, thus purifying the tube wall. In addition, bromine Br easily binds to the free rare earth metal decomposed at the high temperature portion in the central part of the arc, thereby reducing the adhesion of the free rare earth metal to the tube wall. As a result, blackening of the tube wall can be prevented, and the luminous flux maintenance factor can be improved. Moreover, since the metal halide lamp of the present invention is lit by direct current, bromine Br having high electronegativity is mainly attracted to the anode side. In this case, since the anode is made larger than the cathode, even if bromine Br causes the erosion of the anode electrode shaft, the electrode shaft is originally thick, so that it is prevented from breaking early.

In general, when a discharge lamp is lit by direct current, the anode becomes hot due to electron impact. At this time, in order to increase the heat resistance, it is necessary to increase the shape of the anode to increase the heat capacity. On the other hand, the cathode is required to rapidly emit electrons and therefore needs to quickly raise the temperature, and therefore is relatively thin to increase the temperature. Therefore, the lamp of the present invention is lit by direct current,
By attracting bromine Br having a high electronegativity to the thick anode side, it is possible to prevent breakage from occurring earlier than when corrosion progresses on the thin cathode side and prolong the life of the electrode.

Furthermore, when direct current lighting is performed, the released rare earth metal ions are electrically attracted to the cathode side,
A so-called catalysis phenomenon occurs. For this reason, the ions of the rare earth metal are kept away from the high temperature center portion of the arc tube and the quartz glass of the tube wall near the anode side, so that the rare earth metal and quartz react in the high temperature portion of the central portion of the arc tube. Suppressed. As a result, devitrification due to turbidity of the quartz is prevented, and a decrease in the amount of light emitted from the lamp is suppressed.

From the above, according to the metal halide lamp of the first aspect, it is possible to prevent blackening of the arc tube and maintain a high luminous flux maintenance rate by increasing the enclosing ratio of bromine. Prevents breakage of the electrode shaft by attracting bromine Br with high electronegativity to the thick anode side,
Therefore, the life of the lamp can be extended.

When the proportion of bromine Br in the halogen is less than 60% in terms of the number of atoms, the amount of bromine Br enclosed is small and the blackening preventing ability of the arc tube deteriorates, and exceeds 90%. Then, the amount of bromine Br, which is excellent in reactivity, is excessively filled, and the electrode shaft breaks faster.

In the lamp according to the second aspect, iodine I is enclosed as a halogen other than bromine, so that the color temperature of the lamp is maintained at an appropriate level and it is easy to combine with a luminescent metal for improving the color rendering property. It is possible to improve the sex.
From this point, it is preferable that all halogens other than bromine among the enclosed halogens are iodine, but if the proportion of iodine among halogens other than bromine is 90% or more in terms of the number of atoms, color rendering improves. I understood.

In the lamp according to the third aspect, the metal halide contains at least one kind of halides of dysprosium, indium and thallium, so that high efficiency and high color rendering can be obtained.

According to the invention of claim 4, the metal halide is
Since at least one kind of halides of dysprosium, neodymium and cesium is contained, the color rendering property becomes high. The lamp according to claim 5, wherein the distance L between the electrodes is L.
Since it is applied to a short arc type metal halide lamp having a length of 15 mm or less, the function as a point light source can be maintained.

The invention according to claim 6 is a floodlighting device comprising the metal halide lamp according to any one of claims 1 to 5 and a reflector for reflecting the light emitted from this lamp. The high luminous flux maintenance rate and the extended lamp life of the metal halide lamp can be effectively used to improve the life characteristics of the light projecting device and prevent devitrification of quartz. Deterioration is suppressed. Therefore, it is possible to prevent the illuminance of the screen from decreasing.

According to a seventh aspect of the present invention, the metal halide lamp is horizontally lit, the lamp axis is arranged along the optical axis of the reflector, and the electrode serving as a cathode during lighting is arranged on the front light projecting portion side of the reflector. Therefore, even if devitrification occurs due to clouding of quartz on the cathode side due to the rare earth metal attracted near the cathode due to the catalysis phenomenon, transparency is maintained on the anode side and the central part, so The emitted light can be effectively directed to the reflecting surface of the reflector, and the deterioration of the light projecting function can be reduced.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in FIGS. The present embodiment is applied to the color liquid crystal projector shown in FIG. 3 described above, and since it is duplicated, its description is omitted. The short arc metal halide lamp of the floodlight shown in FIG. 1 may have almost the same structure as the conventional short arc metal halide lamp of FIG. 4, and the short arc metal halide lamp of FIG. 1 is different from the conventional one. The electrode is the anode 21
a and the cathode 21b, and the anode 21a
Is thicker than the cathode 21b, and is a point to be lit by direct current by a high frequency.

That is, the short arc metal halide lamp 1 shown in FIG. 1 has a rated input of 250 W, and the light emitting part of the arc tube 20 is a substantially elliptical rotating body made of quartz glass having a thickness of 1.4 mm. Has a major axis of about 15 mm and a minor axis of about 10.5 mm, and has an internal volume of about 0.9 CC. The electrodes sealed at both ends of the arc tube 20 are, for example, one anode 21a made of a tritan rod having a diameter of 1.6 mm and the other cathode 21b made of a tritan rod having a diameter of 0.6 mm.
The distance L between the electrodes 1a and 21b is 6 mm.

In the arc tube 20, 20 mg of mercury, 1.0 mg of dysprosium bromide DyBr ₃ and 0.375 of dysprosium iodide DyI ₃ were used as metal halides.
mg, cesium iodide CsI 0.125 mg, tin bromide Sn
Br ₂ 0.6 mg, indium bromide InBr 0.2 m
g, 0.4 mg of thallium bromide TlBr is enclosed,
Argon Ar is filled as a rare gas at room temperature at 300 Torr. In this case, in all halogens, bromine Br
Is 86.8% in terms of the number of atoms.

In such a lamp 1, the base 24 and the external lead wire 25 are connected to the DC power source 70 to supply the lamp power of 25.
By lighting at 0 W, the tube wall load is 40 to 100 W
Used under a large load condition of about / cm ² . Such a short arc metal halide lamp 1 has a lamp axis O ₁ -O.
₁ is attached to the reflector 2 so that the center axis of the reflector 2, that is, the optical axis O ₂ —O ₂ is substantially aligned. In this case, the cathode 21b of the lamp 1 is positioned on the front light projecting portion side of the reflector 2. A heat insulating film 28 made of a heat resistant oxide such as alumina is formed at least on the outer side of the arc tube on the cathode 21b side.

The operation of the projection light source device 50 having such a configuration will be described. As shown in FIG. 1, the light projecting light source device 50 is used with the reflector 2 having its optical axis O ₂ -O ₂ oriented substantially horizontally, and the short arc metal halide lamp 1 is lit horizontally. This lamp has a color temperature of 7500 K and a lamp efficiency of 82 lm / W when operated with a lamp power of 250 W.

Since the short arc metal halide lamp 1 has a relatively large amount of bromine Br as a halogen, the low melting point alloy of floating tungsten W and silicon Si which tends to adhere to the tube wall. It has a function of returning to the electrode by combining with tungsten, and therefore, the tube wall can be purified, the tube wall can be prevented from being blackened, and the luminous flux maintenance factor can be improved.

Moreover, since this lamp 1 is connected to the DC power source 70 and is lit by direct current, bromine B having a high electronegativity is obtained.
r is attracted to the anode 21a side, and the bromine density becomes high on the anode 21a side. Such bromine may react with W formed at the base of the electrode shaft and tungsten W of the low melting point alloy of Si and carry to the high temperature electrode tip, and thus the base of the electrode shaft may be thinned. However, since the electrode shaft of the anode 21a is made thick in order to increase the heat capacity and heat resistance, a problem such as breaking of the electrode does not occur even if it is slightly thin. Therefore, it is possible to prevent a decrease in life due to breakage of the electrode.

Further, since the rare earth metal is attracted to the cathode 21b side by the catalysis phenomenon, the rare earth metal can be kept away from the high temperature portion, and the whitening due to the reaction between the rare earth metal and quartz is prevented. Further, even if devitrification occurs in the arc tube due to turbidity, it is concentrated in the vicinity of the cathode 21b, and it is possible to prevent devitrification from occurring at the center of the light emitting portion or the anode side.

For example, in the case of the above lamp, 2
Even after lighting for 000 hours, no blackening of the arc tube was observed, of course no breakage of the electrodes occurred, and no clouding of the tube wall was observed. Further, among the enclosed halogens, the halogens other than bromine Br occupy 90% or more of the atomic ratio of iodine I, so that they react well with the rare earth metal that enhances the color rendering, and the color rendering can be enhanced. .

Particularly, in the case of the short arc metal halide lamp 1 having an electrode distance of 15 mm or less, it is advantageous that it is close to a point light source. The advantage can be further utilized.

From this, it is possible to prevent a decrease in the amount of light projected from the light projecting light source device 50, and the screen 1
It is possible to suppress a decrease in illuminance of 0, and as shown in FIG. 2, it is possible to maintain the luminous flux on the screen 10 surface at 80% or more of the initial level even after lighting for 2000 hours.

Explaining an example of a lamp having other specifications, the arc tube 20 has a major axis of about 10 mm and a minor axis of about 9.0.
It is formed so as to have a size of mm and has an internal volume of approximately 0.5 CC. The electrodes sealed at both ends of the arc tube 20 are
One is, for example, an anode 2 made of a tritan rod having a diameter of 1.2 mm.
1a and the other is a cathode 21b made of a tritan rod having a diameter of 0.5 mm, for example, and the electrode-to-electrode distance L between these electrodes 21a and 21b is 5 mm. In the arc tube 20,
13 mg of mercury, 0.5 mg of dysprosium bromide DyBr ₃ as a metal halide, neodymium iodide Nd
0.35 mg of I ₃ and 0.12 of cesium iodide CsI
5 mg and 0.2 mg of tin bromide SnBr ₂ were enclosed, and 300 Ar of argon Ar was enclosed at room temperature as a rare gas. In this case, the proportion of bromine Br in all the halogens is 67% in terms of the number of atoms.

This lamp is 2,000 at 180W DC.
After lighting for a while, as shown in FIG. 2, the luminous flux on the screen 10 surface could be maintained at 74% of the initial value. As can be seen from the above example, the encapsulation ratio of bromine Br is preferably 60 to 90% in terms of atomic number ratio. That is, FIG. 2 shows the screen 10 when the encapsulation ratio of bromine Br is variously changed.
The luminous flux maintenance ratio on the surface was investigated. When the bromine Br is less than 60% in atomic number ratio, the luminous flux is reduced due to blackening or clouding of the tube wall, and the screen 10 after lighting for 2000 hours Since the luminous flux maintenance factor on the surface is lower than the initial 70%, the bromine Br inclusion amount is desired to be 60% or more in terms of atomic number ratio.

If the bromine Br content exceeds 90%, the electrode becomes thinner due to the high reactivity of bromine Br, causing early breakage. In addition, since the proportion of iodine I decreases, the reaction with the rare earth metal having excellent color rendering properties in which iodine I plays a role decreases, the color temperature deteriorates, and the color rendering property decreases,
Moreover, the light emission is significantly reduced, and sufficient efficiency and color rendering cannot be obtained.

For these reasons, the proportion of bromine Br in halogen is desired to be 60 to 90% in terms of the number of atoms. Further, iodine I has a function of reacting with a rare earth metal having an excellent color rendering property to maintain the color temperature of the lamp at an appropriate level and improving the color rendering property, so that the presence of iodine cannot be ignored. From this point, bromine Br in the enclosed halogen is
It is preferable that all halogens other than iodine are iodine I,
It was found that there is no problem in practice if the proportion of iodine I in halogens other than bromine Br is 90% or more in terms of the number of atoms.

In the light projecting device of FIG. 1, when the cathode 21b is arranged on the front light projecting side of the reflector 2, even if quartz becomes cloudy near the cathode 21a due to the catalysis phenomenon. Since the transparency is maintained on the side of the anode 21a and in the central portion, the light emitted from the arc tube 20 is effectively directed to the reflecting surface 31 of the reflector 2, and the deterioration of the light projecting function is reduced.

The present invention is not limited to the above embodiments. That is, in the metal halide lamp of FIG. 1, the structures of the anode 21a and the cathode 21b are different, but both the anode 21a and the cathode 21b are formed by winding an electrode coil around the electrode shaft, like the electrode shown in FIG. You may. However, the anode 21a needs to have a larger heat capacity by making both the electrode shaft and the electrode coil thicker than the cathode 21b. Further, in the present invention, the direct current lighting is not a direct current in a strict sense, but a rectified alternating current,
It may be pulse lighting.

[0055]

As described above, according to the present invention, since the amount of bromine as a halogen is increased, it is possible to prevent the blackening of the arc tube and maintain a high luminous flux maintenance rate, and further, it is operated by direct current and is electronegative. Since bromine having a high degree is attracted to the side of the anode having a large shape, it is possible to prevent early breakage of the electrode due to the thick electrode, and thus the life characteristics of the lamp are significantly improved.

When such a metal halide lamp is used as a light source of a light projecting device, it is possible to prevent a decrease in illuminance on an object to be irradiated such as a screen, maintain a high luminous flux for a long time, and Since the state of the point light source is maintained for a long period of time, there is an effect that it is possible to reduce color unevenness between the central part and the peripheral part on the irradiated surface.

[Brief description of drawings]

FIG. 1 is a sectional view showing a light projecting device including a metal halide lamp and a reflector according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram in which the relationship between the enclosing ratio of bromine, the lighting time of the lamp, and the luminous flux maintenance factor on the screen is measured.

FIG. 3 is an explanatory diagram showing the principle of a color liquid crystal projector.

FIG. 4 is a cross-sectional view showing a conventional light projector including a metal halide lamp and a reflector.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal halide lamp 2 ... Reflector 4, 7, 8, 11 ... Dichroic mirror 6, 12, 13 ... Liquid crystal panel 10 ... Screen, 20 ... Arc tube 21a ... Anode 21b ... Cathode 70 ... DC power supply

Claims (7)

[Claims] 1. A metal halide lamp in which electrodes are sealed at both ends of an arc tube, and mercury, at least a halide of a rare earth metal, and a rare gas are sealed in the arc tube. The proportion of bromine among them is in the range of 60 to 90% in atomic number ratio, and the voltage of the direct current component is applied to the above electrodes to turn on this lamp by direct current, and the electrode which becomes the anode during lighting is the electrode which becomes the cathode. A metal halide lamp characterized by being formed larger than 2. The halogen other than bromine among the halogens enclosed in the arc tube contains iodine, and the proportion of this iodine is 90% or more in terms of atomic number ratio. Metal halide lamp. 3. The metal halide according to claim 1, wherein the metal halide contains at least one kind of halides of dysprosium, indium, and thallium.
Metal halide lamp described in. 4. The metal halide according to claim 1, wherein the metal halide contains at least one of dysprosium, neodymium, and cesium halides.
Metal halide lamp described in. 5. The metal halide lamp according to claim 1, wherein the lamp is a short arc type metal halide lamp having a distance L between the electrodes of 15 mm or less. 6. A metal halide lamp according to any one of claims 1 to 5, and a reflector for reflecting light emitted from the lamp.
A light projecting device comprising: 7. The metal halide lamp is horizontally lit, the lamp axis is arranged along the optical axis of the reflector, and the electrode serving as a cathode during lighting is arranged on the front light projecting portion side of the reflector. The light projecting device according to claim 6.