JPH10134767A - Metal halide lamp with transparent insulation coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal halide lamp in which wetting of a luminescent tube is enhanced while improving transmission rate of a visible light ray area, stability of a color temperature is ensured, missing of transmission of a luminescent tube is restrained, and efficiency is unproved. SOLUTION: A metal halide, a mercury, and a starting gas is sealed therein, and application-type non-transparent metal oxide insulation coating film 3 is formed on one end surface of a luminescent tube 2 provided with electrode 1, 1 on both ends thereof, and the material has characteristics in which an average transmission rate in visible light ray area of 3280 to 780nm is 94% or more, and an acreage reflection factors in an infrared ray area of 780 to 1500nm and 780 to 4000nm are 10 to 30% both on the remaining luminescent tube surface. A transparent insulation coating film 4 made of a plurality of layers of three or more layers of two of more kinds of metal oxides selected from Ta2 O5 , TiO2 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an effect of keeping the entire area of a light emitting portion of an arc tube warm, has excellent color temperature stability, and improves efficiency while suppressing progress of devitrification of the arc tube. The present invention relates to a metal halide lamp which has a high transmittance characteristic in the visible light region.

[0002]

2. Description of the Related Art Conventionally, metal halide lamps have been used for various purposes because of their high efficiency, long life and excellent color rendering properties. In particular, in recent years, the color rendering properties have been remarkably improved, and they have been widely used in commercial spaces such as boutiques and department stores where high-quality color rendering properties are required.

[0003] Originally, mercury lamps and metal halide lamps have been used for outdoor use on highways, outdoor sports facilities, streets, and the like. Therefore, the use of a large number of metal halide lamps on the same floor or the use of OHPs, liquid crystal projectors, and the like as optical light sources, which have not been considered in the past, have been increasing.

Therefore, unlike a conventional outdoor space or a sports facility having a high ceiling even indoors, a large number of metal halide lamps having the same characteristics have been used side by side in the same space in the same room having a low ceiling. ing. However, since the characteristics of the metal halide lamp, which should have the same characteristics, change over time, variations in the characteristics of the individual lamps may be felt as unnatural. In particular, since a metal halide lamp has a large change in color temperature at the initial lighting, a sense of discomfort due to the difference is remarkable.

[0005] In the case of metal halide lamps, the color temperature of the lamp generally tends to decrease with time, and the amount of change in the color temperature of the same type of lamp also differs slightly. What feels particularly uncomfortable is the rapid change in the color temperature of the metal halide lamps installed at the same time on the same floor and having the same color temperature in the initial lighting period of about 100 hours to 300 hours. For this reason, a difference occurs in the color temperatures of a large number of lamps on the same floor, and as a result, the user feels discomfort. A further problem arises when some lamps are burned out and replaced after a long use. In this case, the sense of discomfort is further increased as compared with the above case.

In the case of an optical metal halide lamp, for example, in use in a projection optical system for a liquid crystal, which has been increasingly used in recent years, if the color temperature changes, the blue and green rays of light projected on a screen are changed. , The balance of red changes, which is extremely inconvenient and is perceived by the audience watching the video as discomfort or discomfort with the color tone of the real image of nature.

Conventionally, as a countermeasure against a change in color temperature, for example, in the case of a double-ended arc tube in which electrode leads are led out from both ends of the arc tube, an opaque white fine powder of a metal oxide such as aluminum oxide or zirconium oxide is used. Is applied to the surface near the electrodes at both ends of the quartz arc tube to form an opaque heat-insulating film, raise the minimum temperature at the arc tube end, raise the vapor pressure of the metal halide, and cool It has been generally used to maintain the color temperature by increasing the point temperature to provide a heat retaining effect.

[0008] This conventional method has been effective to some extent. However, the drawback of this method is that when the metal oxide coating area increases, the heat retention effect increases, but the light emitting area to the outside decreases. Increasing the luminous area has the problem that the heat retaining effect is reduced, and also has the problem that the heat retaining effect of the untreated arc tube portion to which the opaque white metal oxide is not applied cannot be expected at all.

Further, quartz, which is commonly used as a material for the arc tube, is transparent in a wide wavelength range from 0.18 μm in the ultraviolet region to 4.0 μm in the infrared region. In other words, there is a problem that, in addition to visible light, light in the infrared and ultraviolet regions that one does not want to emit outside is also transmitted.

Therefore, the following proposals have conventionally been made to improve the heat retaining effect of the arc tube. That is, some proposals have been made to form a transparent heat insulating film made of a metal oxide on the surface of a portion of the arc tube surface where the opaque heat insulating film is not applied, and to keep the arc tube warm by the heat insulating effect. As one of them, there has been proposed a film in which a transparent heat insulating film is formed by an infrared reflecting film composed of a multilayer film (Japanese Patent Publication No. 7-101604). This multilayer infrared reflective film is formed by simply alternately laminating a thin film having a high refractive index such as titanium oxide (TiO ₂ ) and a thin film having a low refractive index such as silicon dioxide (SiO ₂ ). It is formed on the arc tube surface using an existing film forming method such as a CVD method, a dipping method, and a sputtering method. On the other hand, by using an absorption film (matte film) made of a metal oxide such as titanium oxide, which has a smaller heat-retaining effect than an infrared reflection film made of a multilayer film, multiple reflections of heat rays reduce the vapor pressure of the filling inside the arc tube. It has also been proposed to measure the rise (Japanese Patent Laid-Open No. 7-14550).

[0011]

However, when an infrared reflecting film comprising the above-mentioned multilayer film is used, light in a narrow range in the near infrared region (780 nm to 1500 nm) is efficiently reflected (average reflectance). However, there is a problem that the temperature inside the arc tube becomes too high, and the devitrification inside the arc tube progresses rapidly with lighting, resulting in a sharp decrease in luminous flux. Furthermore, since the arc tube itself becomes too high in temperature, there is a major drawback in that if a minute crack is present at the end of the arc tube, the arc tube will burst. On the other hand, in the case where an absorption film made of a metal oxide is provided, the devitrification is suppressed more than in the case of the infrared reflection film by forming the absorption film of the metal oxide on the surface of the arc tube. Due to the absorption and high index of refraction of the film, a significant reduction in luminous flux, ie a reduction in efficiency, was unavoidable.

As described above, the conventional proposal of applying a transparent heat insulating film made of a metal oxide to the surface of an arc tube and measuring the increase in vapor pressure of the sealed substance inside the arc tube by the heat insulating effect has been proposed. Transparent thermal insulation film (multilayer infrared reflective film)
Since the application of the method involves devitrification of an arc tube or absorption or coloring caused by the presence or high refractive index of a metal lower oxide that is not sufficiently oxidized and that constitutes an absorption film, the metal is not necessarily used. It did not lead to emission of larger light energy to the outside of the arc tube than before the application of the transparent heat insulating film of oxide, that is, improvement of luminous efficiency.

On the other hand, the applicant of the present application firstly deposits a metal oxide such as Ta ₂ O ₅ or TiO ₂ having a higher optical refractive index than the material of the arc tube (quartz) on the surface of the arc tube. Film thickness is λ
/ 2 (λ: any wavelength in the visible light region), and a metal halide lamp provided with a single-layer transparent heat insulating film having a transparent characteristic in the visible light region and formed. In the metal halide lamp provided with a single-layer transparent heat insulating film according to this proposal, the external emission of a part of the light in the infrared region is suppressed over the entire region of the effective quartz arc tube without substantially reducing the light in the visible light region. Multi-reflection within the arc tube to maintain high luminous efficiency at lower tube wall loads, prevent devitrification inside the arc tube, and thereby maintain a stable color temperature and maintain luminous flux for a long period of time .

As described above, the metal halide lamp proposed above has a single-layered transparent heat-insulating film formed on the surface of the arc tube to improve the heat-insulating effect and improve the luminous characteristics peculiar to the metal halide lamp such as color temperature stability. Although it can be improved, there is a problem that the transmittance in the visible light region is slightly reduced by the single-layer transparent heat insulating film.

The present invention has been made in order to solve the above-mentioned problems in the conventional and previously proposed metal halide lamps. A transparent heat insulating film made of a metal oxide is provided on the surface of the arc tube as in the conventional and previously proposed metal halide lamps. Applicable, transparent heat insulation film capable of increasing the use efficiency of light radiated from the arc tube as much as possible compared to the untreated arc tube, and allowing gentle reflection in a much wider area than the conventional infrared reflection film. It is another object of the present invention to provide a metal halide lamp capable of suppressing the devitrification of the arc tube and improving the luminous efficiency as compared with before the application of the heat retaining film, together with the stability of the color temperature.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a quartz arc tube in which a metal halide, mercury and a starting gas are sealed, and a pair of electrodes are arranged inside. In the metal halide lamp having an average transmittance of 380 nm to 780 nm in a visible light region of 94% or more, an average reflectance of an infrared region of 780 nm to 1500 nm, and an average of an infrared region of 780 nm to 4000 nm, Ta, which has the property that the reflectance is 10 to 30%
₂ O ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Al
_This is to provide a multilayer transparent heat insulating film composed of a plurality of three or more layers formed by forming two or more types of metal oxides selected from the group of ₂ O ₃ and SiO ₂ . Here, the average transmittance of the multilayer transparent heat insulating film means that light generated inside the arc tube is formed on the entire back surface of the arc tube base (made of quartz glass) on which the multilayer transparent heat insulating film is formed in the thickness direction. → substrate → interface between the substrate and the multilayer transparent thermal insulation film → multilayer transparent thermal insulation film → multilayer transparent thermal insulation film surface → means the average value of the light transmittance for each wavelength when passing linearly in the order of external. Further, the average reflectance of the multilayer transparent heat insulating film means a value obtained by subtracting the average transmittance of the multilayer transparent heat insulating film from 100%.

The multilayer transparent heat insulating film having such a structure has the same spectral characteristics as a so-called "antireflection film" that transmits as much light as possible in the visible light region (the metal oxide in the film is not sufficiently oxidized). The absorption in the visible light region is almost zero). On the other hand, the infrared region has a shallow and wide reflection band even in the near-infrared region (780 nm to 1500 nm), and has a characteristic of partially reflecting the heat ray over a wide region. Therefore, the multilayer transparent heat-insulating film having such characteristics is capable of improving the transmittance in the visible light region, stabilizing the color temperature, and suppressing the devitrification inside the arc tube and improving the lamp efficiency. It can exhibit a heat retaining effect.

In the present invention, the reason why the average transmittance in the visible light region of the multilayer transparent heat insulating film is 94% or more is as follows.
In order to maximize the efficiency of using light emitted from the arc tube by increasing the transmittance (92%) of the arc tube itself made of quartz, the average reflectance in the infrared region of 780 nm to 1500 nm and 780 nm to 4000 nm The reason why each is set to 10 to 30% is that if the average reflectance is less than 10%, the heat retention effect is reduced due to insufficient reflectance itself, and if the average reflectance exceeds 30%, considerable lamination is performed. This is because a large number is required, and a large ripple occurs in the spectral transmittance curve in the visible light region, and it becomes difficult to maintain the average reflectance in the visible light region at 94% or more. The multilayer transparent heat insulating film is composed of three or more multilayer films because the average reflectance in the infrared region may be less than 10% in a two-layer film.

[0019]

Next, an embodiment will be described. FIG. 1 is a diagram showing an embodiment of a metal halide lamp according to the present invention. In this embodiment, a metal halide lamp composed of a single arc tube without using an outer bulb is 70 W.
3 shows a short arc metal halide lamp of the present invention.
In FIG. 1, reference numeral 1 denotes an electrode, 2 denotes a quartz arc tube, 3 denotes an opaque heat insulating film having the same configuration as that of the conventional art, and 4 denotes a multilayer transparent heat insulating film according to the present invention. The quartz arc tube 2 is mainly filled with scandium (Sc) and sodium (Na) iodides, mercury (Hg), and a starting gas composed of an inert gas such as argon. The dimension of the spherical portion of the arc tube 2 in the major axis direction is 11 mm, and the arc length is 2.7 mm. Arc tube 2
An opaque metal oxide is applied over the region from the other end of the arc tube 2 to 2 mm of the spherical portion so that the reflecting mirror is disposed on one end side of the light emitting tube. As the heat insulating film 3, a multilayer transparent heat insulating film 4 is formed over the entire area of the remaining 9 mm of the spherical portion by, for example, a CVD method. The multilayer transparent heat insulating film 4 in this embodiment is made of Ta ₂
It is composed of a four-layer film composed of an O ₅ film and a SiO ₂ film. The optical refractive index and the physical film thickness of each layer are shown in Table 1.
The optical refractive index is a value at a wavelength of 500 nm.

[0020]

[Table 1]

The tube wall load of the arc tube configured as described above is
The short arc metal halide lamp of this configuration is 55 W / cm ² and is often used in combination with a reflector.
FIG. 2 shows an example of the configuration. In FIG. 2, reference numeral 5 denotes a reflecting mirror, and the opaque heat insulating film 3 is formed by coating only on one side of the arc tube 2 on the opening side of the reflecting mirror 5 in consideration of the efficiency of using the reflecting mirror 5 and light rays.

Next, the spectral transmission characteristics of the above-described four-layered multilayer transparent heat insulating film will be described. FIG. 3 shows the spectral transmission characteristics in the visible light region, and FIG. 4 shows the spectral transmission characteristics in the infrared region.
Each of them is shown in comparison with the spectral transmission characteristics of the single-layer transparent heat insulating film and the infrared reflective film, and FIG. 3 also shows the characteristics of the untreated arc tube itself without a film. The single-layer transparent heat-insulating film has an optical thickness of Ta ₂ O ₅ of λ /
2 (peak wavelength λ: 510 nm)
Further, as the infrared reflecting film, an alternate multilayer film formed by alternately stacking six films of Ta ₂ O ₅ and SiO _{2 having} an optical film thickness of λ / 4 (peak wavelength λ: 920 nm) is used. . FIG. 5 shows the visible light region and the infrared light region based on the measured values of the spectral transmittances of the multilayer transparent heat insulating film, the single-layer transparent heat insulating film, and the infrared reflective film according to the present embodiment shown in FIGS. Is a plot of the average reflectance at. In addition,
Visible light region is a wavelength range of 380 nm to 780 nm, for the infrared region, to secure the short wavelength end to 780 nm, is changed to 500nm every long wavelength end lambda _L to 4000nm from 1500 nm, an average reflectance in each wavelength range Calculated and shown. In FIG. 5, a curve a indicates the multilayer transparent heat insulating film according to the present embodiment, a curve b indicates a single-layer transparent heat insulating film, and a curve c indicates the average reflectance of the infrared reflective film.

As can be seen from FIG. 5, first, in the visible light region, the multilayer transparent heat insulating film having a four-layer structure in the present embodiment has an average transmittance of 95% (average reflectance of 5%).
The transmittance of visible light is the highest among the three, and is higher than the transmittance (92%) of the untreated arc tube itself before the formation of the heat insulating film. On the other hand, in the infrared region, in the average reflectance from the long wavelength end (780 nm) to the wavelength of 1500 nm in the visible light region, the transparent insulating film having a four-layer structure in the present embodiment is 18%, the lowest among the three. However, when compared with the average reflectance in the entire infrared region transmitting through the quartz arc tube, that is, in the range from 780 nm to 4000 nm, the difference between them is about 18%, and there is almost no difference. This tendency is substantially the same not only in the multilayer transparent heat insulating film having the four-layer structure of the present embodiment but also in the multilayer transparent heat insulating film having the three or more layers.

As described above, in the metal halide lamp according to the present embodiment, the multilayer transparent heat insulating film having the above-mentioned structure is applied to the surface of the arc tube, and the high visible light transmittance prevents the reduction of the luminous flux and improves the efficiency. On the other hand, by gently reflecting a wide range of infrared rays, devitrification of the arc tube is suppressed, and the color temperature is stabilized.

FIG. 6 shows a lamp in which several types of multi-layered transparent heat insulating films are formed on the arc tube of a metal halide lamp having the same structure as that of the embodiment shown in FIG. Average reflectance of each film at 1500 nm)
It is a figure showing the result of having investigated the relation with the rate of change of lamp efficiency before and after film application. Note that the average reflectance in the near-infrared region (780-1500 nm) is used as the average reflectance of each film, as shown in FIG. This is because it is a region that appears greatly.

As for the number of layers of the multilayer transparent heat insulating film, design studies were conducted from two to seven layers, and among them, five types of lamps having two to five transparent heat insulating films were prepared. Of the five types of lamps, four types are the multilayer transparent heat-insulating films according to the present invention, which include those having the film configurations shown in Table 1, and the results of the investigation are indicated by circles in FIG. Have been. In addition, as a comparative example, the lamp having the remaining one kind of the two-layered transparent heat-insulating film is shown as a comparative example by the black circles. In addition, two types of metal halide lamps to which two types of single-layer transparent heat insulating films having different film materials and film thicknesses are applied, and two types of infrared rays having different numbers of layers, for comparison with the lamp provided with the multilayer transparent heat insulating film. Two types of metal halide lamps to which respective reflective films were applied were prepared, and the results of similar investigations were indicated by □ and Δ, respectively.

As can be seen from FIG. 6, in the metal halide lamp using the multilayer transparent heat insulating film according to the present invention,
The average reflectance at 780-1500 nm is 10% or more and 30% even if the number of layers, film thickness, etc. of the films constituting the multilayer transparent heat insulating film are different.
In the following cases, the lamp efficiency is improved by about 1 to 2%. On the other hand, in the metal halide lamp provided with the single-layer transparent heat insulating film and the infrared reflective film, it is apparent that the lamp efficiency is generally inevitably reduced by about 1%. Incidentally, even when the same multilayer transparent heat insulating film having an average transmittance in the visible light region of 94% or more is used, 780 to 1500 nm
If the average reflectance is less than 10% (the number of layers is 2 layers or less), the heat retention effect is insufficient due to the lack of reflectance itself, and if it exceeds 30% (the number of layers is approximately 20 layers or more), , To cause a large ripple in the spectral transmittance curve in the visible light region,
It is difficult to maintain the average reflectance in this region at 94% or more, and the improvement in lamp efficiency is less than 1%, which is not preferable.

FIG. 7 shows the emission characteristics (solid line) of the metal halide lamp comprising the arc tube of the present embodiment after the formation of the multilayer transparent heat insulating film, and the emission characteristics of the metal halide lamp comprising the arc tube before the formation of the multilayer transparent heat insulating film (solid line). Table 2 also shows various characteristics of the metal halide lamp having the multilayer transparent heat insulating film of the present embodiment formed thereon, and Table 2 shows the characteristics of the metal halide lamp including the arc tube before the formation of the multilayer transparent heat insulating film. Are shown in comparison with the various characteristics.

[0029]

[Table 2]

As can be seen from FIG. 7, in the metal halide lamp according to the present embodiment, the light emission of Hg is suppressed by the heat insulating effect of the multilayer transparent heat insulating film, and conversely, the light emission of the added metal halide Sc unique to the metal halide lamp is promoted. You can see that it is done. For the emission of Na, N
As the vapor pressure of a increases, the peak intensity decreases due to self-absorption, while the peak width increases somewhat. Therefore,
As shown in FIG. 7, the decrease in the peak intensity of Na emission and the increase in the peak width indicate that the heat retaining effect of the film is obtained. In Table 2, this corresponds to the lamp characteristic change in which the color temperature is lowered and the color rendering index is improved in the present embodiment in which the multilayer transparent heat insulating film is formed as compared to before the film formation. In Table 2, further improvement of the total luminous flux and efficiency, and lamp voltage and Duv
(Distance from the blackbody locus) shows little change.

As described above, the multilayer transparent heat insulating film in the present embodiment not only functions as an anti-reflection film in the visible light region, but also increases the vapor pressure of the filling in the arc tube due to the gentle reflection function in the infrared region. This has the effect of keeping the heat warm, and as a result, contributes to the improvement of the lamp efficiency and a slight increase in the total luminous flux.

In order to check the progress of devitrification in the metal halide lamp according to the present embodiment, a lighting test was performed.
No devitrification of the arc tube was observed even after the lapse of 00 hours.

In the above-described embodiment, the multi-layer transparent heat insulating film having the film configuration shown in Table 1 is used.
Not only this film configuration but also the visible light range (380 ~ 780
780nm ~ 1500nm with average transmittance over 94%
As long as the average reflectance in the infrared region and the average reflectance in the infrared region of 780 to 4000 nm both have a characteristic of 10 to 30%, the same effect as that described in the above embodiment can be obtained. Further, when the tube wall load of the arc tube using the multilayer transparent heat insulating film having such characteristics is 40 to 70 W / cm ² , an excellent effect is exhibited, that is, the heat insulating effect of the multilayer transparent heat insulating film on the arc tube is remarkably exhibited. Thus, the light emission characteristics can be improved by increasing the vapor pressure, the lamp efficiency can be improved, and the lamp lighting posture can be arbitrarily selected by making the arc tube wall temperature uniform. In addition, tube wall load is 70W / cm
^If it exceeds ² , the luminous flux maintenance factor becomes small and the service life becomes short, and the color rendering index Ra deteriorates.
If it is less than / cm ² , light emission of the encapsulated metal does not occur, the color temperature becomes extremely high, and the color rendering property deteriorates. Therefore, the tube wall load is preferably set to 40 to 70 W / cm ² .

In the above embodiment, the lamp of 70 W is shown, but if the output of the lamp is 150 W or less,
The same effect can be obtained by forming the multilayer transparent heat insulating film. However, in the case of a lamp having a lamp output exceeding 150 W, the lamp wall load may exceed 70 W / cm ² and the color rendering index Ra may be deteriorated. Therefore, the lamp output is preferably set to 150 W or less. In the above embodiment, the arc length of the arc tube is set to 2.7 mm.
The same effect can be obtained even when the above-mentioned multilayer transparent heat insulating film is formed for an arc tube having an arc length of.

[0035]

As described above with reference to the embodiments, according to the present invention, the average transmittance in the visible light region is 94%.
A transparent heat insulating film composed of a plurality of three or more layers having characteristics such that the average reflectance in the infrared region of 780 nm to 1500 nm and the average reflectance in the infrared region of 780 to 4000 nm are both 10 to 30%. Therefore, the heat retention of the arc tube is enhanced while the transmittance in the visible light region is improved, the color temperature is stabilized, the devitrification of the arc tube is suppressed, and the lamp efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a metal halide lamp according to the present invention.

FIG. 2 is a diagram showing an embodiment in which the metal halide lamp according to the embodiment shown in FIG. 1 is used in combination with a reflector.

FIG. 3 is a diagram showing the spectral transmission characteristics in the visible light region of the multilayer transparent thermal insulation film in the embodiment shown in FIG. 1 in comparison with the spectral transmission characteristics of a single-layer transparent thermal insulation film and an infrared reflective film.

FIG. 4 is a view showing the spectral transmission characteristics of the multilayer transparent heat insulating film in the infrared region in comparison with the spectral transmission characteristics of the single-layer transparent heat insulating film and the infrared reflective film.

FIG. 5 is a diagram showing the average reflectance of a multilayer transparent heat insulating film in comparison with the average reflectance of a single-layer transparent heat insulating film and an infrared reflective film.

FIG. 6 is a diagram showing a change in a change rate of a lamp efficiency with respect to a change in an average reflectance in a near infrared region of a metal halide lamp using a multilayer transparent heat insulating film, a single-layer transparent heat insulating film, and an infrared reflecting film.

FIG. 7 is a view showing emission characteristics of an arc tube before and after forming a multilayer transparent heat insulating film in the metal halide lamp according to the embodiment shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 arc tube 3 opaque heat insulating film 4 multilayer transparent heat insulating film 5 reflector

Claims (2)

[Claims] 1. A metal halide lamp having a quartz arc tube in which a metal halide, mercury and a starting gas are sealed and a pair of electrodes are arranged inside, wherein a surface of the arc tube has a wavelength of 380 nm to 780 nm. Ta has a characteristic that the average transmittance in the visible light region is 94% or more, and the average reflectance in the infrared region from 780 nm to 1500 nm and the average reflectance in the infrared region from 780 nm to 4000 nm are both 10 to 30%.
₂ O ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Al
A metal halide lamp comprising a multilayer transparent heat insulating film composed of a plurality of three or more layers formed by forming two or more types of metal oxides selected from the group consisting of ₂ O ₃ and SiO ₂ . 2. The light-emitting tube according to claim 1, wherein the light-emitting tube has no outer bulb and is exposed, the tube wall load is 40 to 70 W / cm ² , and the lamp output is 150 W or less. Metal halide lamp.