JPH07122233A - High pressure discharge lamp - Google Patents

Abstract

PURPOSE:To provide a metal halide lamp having a high lumen maintainance factor and a long lifetime by preventing sputter of electrode while the lamp is being lighted, and reducing the blackening of a light emitting tube. CONSTITUTION:A light emitting tube includes a light emission part 1 in which a pair of electrodes 2, 3 are installed sealedly, and mercury, rare gas for starting, and metal halide are encapsulated in this light emission part 1. These electrodes 2, 3 are made of a material within the range 0.5<=TaC/HfC<=5.0, This permits suppressing the blackening of the tube inner wall to lead to achievement of a long lifetime.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high pressure discharge lamp having at least one pinch seal portion, which is applied to a metal halide lamp or the like, and more particularly to an improvement of its electrode.

[0002]

2. Description of the Related Art In recent years, high pressure discharge lamps such as metal halide lamps, sodium lamps and xenon lamps have been installed on roads,
In addition to wide area lighting such as open spaces and stadiums, there is an increasing demand for indoor lighting in stores and the like. In particular, metal halide lamps are widely used and widely used as light sources for overhead projectors, overhead type liquid crystal projection televisions, projectors, etc., in addition to lighting for display products, because of their high color rendering properties and high efficiency.

A conventional high pressure discharge lamp will be described below by using an example of a metal halide lamp with reference to the drawings. FIG. 3 is a front view showing a metal halide lamp which is a type of conventional high pressure discharge lamp. In FIG. 3, reference numeral 11 denotes an elliptical arc tube made of quartz glass,
Metal foil conductors 14 and 15 connected to a pair of electrodes 12 and 13 containing tungsten (W) as a main component are sealed at both ends. The other ends of the metal foil conductors 14 and 15 are connected to an external lead. -The wires 16, 17 are connected. Arc tube 1
1 is filled with mercury, a metal halide, and a rare gas for starting. When the lamp is turned on, the metal halide melts, and the metal halide transported to the high temperature part at the electrode tip evaporates violently. Therefore, the density of the metal halide in the arc becomes extremely high, the emission spectrum peculiar to the metal halide increases, and a highly efficient and high color rendering lamp can be obtained.

[0004]

However, in general, a high pressure discharge lamp such as a metal halide lamp has a problem that the luminous flux maintenance rate is greatly reduced during its life. That is, the decrease in the luminous flux maintenance factor during the lifetime is caused by the excessive temperature rise of the electrode tip during lighting, which causes tungsten (W), which is the main constituent material of the electrode, to scatter, and is transported by convection in the arc tube and adheres to the tube wall. The blackening phenomenon occurs, and the blackening of the tube wall blocks the transmission of visible light generated in the arc tube.

In view of the above problems, the present invention provides a high pressure discharge lamp which suppresses electrode scattering at the electrode tip, prevents blackening of the arc tube throughout the life of the lamp, and obtains a high luminous flux maintenance factor. With the goal.

[0006]

In order to solve the above-mentioned problems, the high pressure discharge lamp of the present invention comprises, as an electrode material, hafnium carbide (HfC) and tantalum carbide (TaC) in a molar ratio.
It is provided with an electrode configured in the range of 0.5 ≦ TaC / HfC ≦ 5.

[0007]

With the above-described structure, the present invention can prevent the scattering of the electrodes during the lighting of the lamp and reduce the blackening of the arc tube as compared with the conventional lamp, and the luminous flux maintenance rate during the life of the lamp is very high. It is possible to provide a high-pressure discharge lamp having a long life and high cost.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A metal halide lamp which is a kind of high pressure discharge lamp will be described below as an embodiment of the present invention with reference to the drawings. FIG. 1 shows a horizontally lit 200 W metal halide lamp arc tube according to an embodiment of the present invention.
This arc tube has a single tube structure that is not housed in the outer tube bulb. In FIG. 1, reference numeral 1 denotes an arc tube light emitting portion having an inner volume of 0.8 cc and made of quartz glass, and has a pair of electrodes 2 and 3 sealed at both ends.
The distance between the electrodes is 5.0 mm. The electrode material is composed of TaC / HfC = 4 in molar ratio. Metal foil conductors 6 and 7 made of molybdenum are sealed in the arc tube sealing portions 4 and 5, and the electrode shafts of the electrodes 2 and 3 are connected to the metal foil conductors 6 and 7, respectively, and The other ends of these metal foil conductors 6 and 7 are connected to external lead wires 8 and 9. Reference numeral 10 is a heat insulating film applied to the outer surface of the tube around the electrodes. Then, in the arc tube light emitting unit 1, 40 mg of mercury, 10 atm of xenon (Xe) gas, and 1 mg of GdI ₃ as a metal halide,
LuI ₃ 0.5 mg, NdI ₃ 0.5 mg, CsI 2 m
g is sealed.

When the lamp assembled as described above was horizontally lit and it was examined how the luminous flux maintenance factor changes with the lapse of lighting time, the results shown in FIG. 2 were obtained. In FIG. 2, the characteristic A is TaC / H as an electrode material.
a metal halide lamp having an electrode with fC = 4,
Characteristic B is a metal halide lamp including an electrode containing W as a main component (99% by weight or more). As can be seen from FIG. 2, the lamp provided with the electrode having TaC / HfC = 4 according to the present embodiment has a luminous flux maintenance factor of about 90% after being lit for 10,000 hours, which is higher than that of the lamp containing W as a main component. It was very expensive. Further, during the lamp life, only a slight blackening of the arc tube due to the scattering of the electrodes was observed.

Although no additive was added to the electrode in the above-mentioned examples, excellent effects were obtained even with an electrode to which an electron emitting substance such as thorium oxide or dysprosium oxide was added.

The reason why such an excellent effect is obtained is that Ta is
This is because the electrode configured with a molar ratio of C / HfC = 4 has a much higher melting point than W, so that the electrode does not easily scatter even if the electrode tip temperature rises excessively. Furthermore, W is a reaction (water cycle) with residual water in the arc tube and S
The scattering of the electrode becomes more intense due to the reaction with i, but HfC
-The TaC electrode is considered to be stable because it hardly reacts with the substance remaining in the arc tube.

Further, the range of TaC / HfC is 0.5 to.
The reason why it is limited to 5 is that Hf is limited to compounds in other ranges.
The characteristics are almost the same as those of the electrode containing C as the main component (99% or more) or the electrode containing TaC as the main component (99% or more). Is.

The electrode of this embodiment is more effective than the conventional electrode containing W as its main component, as the electrode operating temperature becomes higher, and a short arc type with an interelectrode distance of 10 mm or less or a tube wall load of an arc tube. Suitable for use in high high watt lamps.

Further, although a lamp having a single tube structure is used in the above-mentioned embodiment, it can be used for a high pressure discharge lamp such as a lamp having a double tube structure, and the same effect as above can be obtained.

[0015]

As described above, according to the present invention, hafnium carbide (HfC) and tantalum carbide (T) are used as electrode materials.
Since the aC) is provided with an electrode having a molar ratio of 0.5 ≦ TaC / HfC ≦ 5, the effect of preventing scattering of the electrode is particularly large, and blackening of the arc tube can be suppressed. As a result, it is possible to obtain a long-life high-pressure discharge lamp having a high luminous flux maintenance rate.

[Brief description of drawings]

FIG. 1 is a front view of a kind of metal halide lamp of a high pressure discharge lamp according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the rate of change in the luminous flux maintenance factor with the passage of lighting time.

FIG. 3 is a front view of a type of metal halide lamp of a conventional high pressure discharge lamp.

[Explanation of symbols]

 1 Quartz glass arc tube light emitting part 2, 3 Electrode 4, 5 Arc tube sealing part 6, 7 Molybdenum metal foil conductor 8, 9 External lead wire 10, Thermal insulation film

 ─────────────────────────────────────────────────── ─── Continued front page (72) Hideaki Omura Inventor Hideaki Omura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kazutaka Koyama 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A high pressure discharge lamp comprising an arc tube having at least one pinch seal portion, wherein hafnium carbide (HfC) and tantalum carbide (Ta) are used as the electrode materials.
A high pressure discharge lamp comprising an electrode made of a material having a molar ratio of C) of 0.5 ≦ TaC / HfC ≦ 5.