JPH0721981A - Metal halide lamp - Google Patents

Abstract

PURPOSE:To obtain a metal halide lamp which can improve the light flux maintaining factor without using an electrode coil or a heat insulating body. CONSTITUTION:To the inside 1a of a luminous tube 1 made of a quartz glass, mercury, a metal iodide, and xenon gas are sealed. And a pair of electrodes 2 sealed on both sides of the luminous tube 1, which feed the lamp power less than 50W are composed of a material made by including 1.0 to 4.0wt.% of sodium oxide to tungsten, by making into a cylindrical rod form with the diameter 0.2 to 0.4mm.

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.

[0002]

2. Description of the Related Art A metal halide lamp is a quartz glass arc tube filled with mercury, a metal halide and a rare gas, and an arc discharge is generated between a pair of electrodes sealed at both ends of the arc tube. This evaporates the metal halide enclosed in the arc tube and utilizes the emission spectrum peculiar to metal.

Since this metal halide lamp has higher efficiency and longer life than an incandescent light bulb, a small metal halide lamp has been developed as a light source to replace the incandescent light bulb in recent years. As a conventional example, there is known a small metal halide lamp capable of instantaneous lighting by enclosing a xenon gas together with a metal iodide in an arc tube at a relatively high pressure.

However, in a small metal halide lamp having a lamp power of 50 W or less, the lamp power is 150
There is a problem that the luminous flux maintenance factor is lower than that of a metal halide lamp of W or more. The cause of such a decrease in the luminous flux maintenance factor during lighting is that the reaction between the metal iodide and the electrode and the deformation of the tip of the electrode evaporate tungsten, which is the material of the electrode, and the blackening film is formed on the inner surface of the arc tube. This is because the light transmittance of the quartz glass arc tube is lowered.

Another cause of the lowering of the luminous flux maintenance factor is that a gap is apt to occur between the electrode of the arc tube and the sealing portion of the quartz glass. If there is a gap between the electrode and the quartz glass, The molten metal iodide enters the gap while the arc tube is lit, and the sealing parts of the electrodes that contact both ends of the arc tube become the coldest part of the arc tube, and the metal iodide that penetrates the sealing part of the electrode. Is not vaporized, and the amount of metal iodide contributing to light emission is reduced.

As a means for preventing the reduction of the luminous flux maintenance factor of the conventional metal halide lamp, an electrode coil is provided at the tip of the electrode to suppress the temperature rise of the tip of the electrode or the electrode serving as the coldest part of the arc tube. It is known to apply a heat retaining body to the end portion of the arc tube including the sealing portion.

[0007]

However, in these means, in a small metal halide lamp, it is difficult to provide an electrode coil at the tip of the electrode because the electrode diameter is small, and the arc tube is small and heat-retaining. It is also difficult to apply a heat retaining body because the influence of light shielding by the body increases.

Therefore, an object of the present invention is to provide a metal halide lamp capable of improving the luminous flux maintenance rate during lighting without using an electrode coil or a heat retaining body.

[0009]

The metal halide lamp of the present invention is a metal halide lamp having a lamp power of 50 W or less, in which 0.1 to 2.0 mg of mercury and 0.01 to 1.0 mg of mercury are internally contained. From sodium iodide, scandium iodide, cadmium iodide, indium iodide, cesium iodide, neodymium iodide, europium iodide, dysprosium iodide, holmium iodide, thulium iodide, thallium iodide and thorium iodide. A mixture of one or more kinds selected from the group consisting of, and a quartz glass arc tube having a discharge space filled with xenon gas at a pressure of 0.1 to 1.0 MPa at room temperature; A pair of electrodes sealed at both ends, the electrodes being made of a material containing 1.0 to 4.0% by weight of thorium oxide in tungsten. , And the diameter 0.2~0.4m
It has a configuration of a cylindrical rod-shaped body of m.

[0010]

According to the structure of the present invention, when electric power is supplied between the pair of electrodes, arc discharge is generated between the electrodes, and light is emitted in the emission spectrum peculiar to the enclosed material. In this case, as the electrode material, tungsten containing 1.0 to 4.0% by weight of thorium oxide was used, and the electrode was formed into a cylindrical rod-shaped body having a diameter of 0.2 to 0.4 mm. Has a good electron emission ability, the temperature rise of the tip portion of the electrode during lighting is suppressed, so that the evaporation of tungsten, which is the main material of the electrode, is reduced, and the blackening of the inner surface of the arc tube can be suppressed. Moreover, the thorium oxide contained in the electrode is also distributed on the surface of the electrode, and the thorium oxide distributed on the surface of the electrode strengthens the sealing between the electrode and the quartz glass of the arc tube. Is prevented, and molten metal iodide during lighting is prevented from entering the electrode sealing portion. Therefore, it is possible to improve the luminous flux maintenance factor during lighting without using a conventional electrode coil or a heat retaining body.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. FIG. 1 schematically shows a small metal halide lamp according to an embodiment of the present invention. In this figure, 0.2 mg of scandium and sodium iodide, 0.8 mg of mercury, and 0.7 MPa of xenon gas are sealed at room temperature in a discharge space 1a inside the arc tube 1 made of quartz glass, and A pair of electrodes 2 is sealed on both ends, and a metal foil 3 and a lead wire 4 are sealed on the sealing portion 1b. And the electrode 2 contains 2.0% by weight of thorium oxide.
It is a cylindrical rod body made of contained tungsten and having a diameter of 0.25 mm.

When a lamp voltage of 85 V was applied to the small metal halide lamp and a lamp power of 35 W was supplied, the initial luminous flux was 3000 lm, and the luminous flux maintenance rate during lighting was as good as 85% even after 2000 hours had elapsed. The reasons why the characteristics of this small metal halide lamp were good will be described below. First, since the thorium oxide contained in the tungsten electrode of the electrode 2 has a low work function and a good electron emission ability, the temperature of the tip of the electrode during lighting is 300 ° C. or more as compared with the one not containing thorium oxide. Because it will be lower
Evaporation of tungsten, which is the main material of the electrode 2, is reduced, and as a result, blackening of the inner surface of the arc tube 1 is suppressed. Further, the thorium oxide existing on the surface of the electrode 2 is strongly bonded to the thorium oxide and the quartz glass during the heat sealing process of the electrode 2 and the quartz glass of the arc tube 1, so that the electrode and the quartz glass are bonded together. There is no gap between them. Therefore, the metal iodide does not enter the sealing portion 1b during lighting, the amount of the metal iodide contributing to light emission does not decrease, and therefore the luminous flux does not decrease.

Next, by changing the content ratio of thorium oxide contained in the electrode 2 and the diameter of the electrode 2, small metal halide lamps constructed in the same manner as in the above-mentioned embodiment were manufactured. The results of the tests are shown in Table 1.

[0014]

[Table 1]

As is clear from Table 1, when the amount of thorium oxide contained in the tungsten electrode is less than 1.0% by weight, as in Experimental Example 2, the temperature of the electrode 2 rises and tungsten vaporizes. As a result, the blackening of the inner surface of the arc tube 1 increases. Further, in this case, a gap is formed in the sealing portion 1b, and the metal iodide penetrates into the gap, so that the luminous flux maintenance factor is significantly reduced.

As in Experimental Example 6, when the content of thorium oxide is 4.0% by weight or more, the blackening of the inner surface of the arc tube 1 due to the evaporation of thorium from the electrode 2 increases and the luminous flux maintenance factor decreases. To do. As in Experimental Example 7, the electrode 2 has a diameter of 0.
When the thickness is 2 mm or less, the temperature of the tip portion of the electrode 2 rises, the evaporation of tungsten increases, the blackening of the inner surface of the arc tube increases, and the luminous flux maintenance factor decreases.

As in Experimental Example 10, the diameter of the electrode 2 is 0.
When it exceeds 4 mm, the gap generated in the electrode sealing portion 1b becomes large, so that the amount of metal iodide penetrating into the gap increases, and thus the luminous flux maintenance factor decreases. Against these,
Like Experimental Examples 1, 3, 4, 5, 8 and 9, the diameter of the electrode 2 was in the range of 0.2 to 0.4 mm, and the electrode 2
Those containing the thorium oxide contained in 1.0 to 4.0 wt% had a good luminous flux maintenance factor.

[0018]

In the metal halide lamp of the present invention, tungsten containing 1.0 to 4.0% by weight of thorium oxide is used as the material of the electrode, and the electrode has a diameter of 0.2 to 0.4 mm. Because it is a cylindrical bar of
Since thorium oxide has a good electron emission ability, the temperature rise of the tip portion of the electrode during lighting is suppressed, so that evaporation of tungsten, which is the main material of the electrode, is reduced, and blackening of the inner surface of the arc tube can be suppressed. Moreover, the thorium oxide contained in the electrode is also distributed on the surface of the electrode, and the thorium oxide distributed on the surface of the electrode strengthens the sealing between the electrode and the quartz glass of the arc tube. Is prevented, and molten metal iodide during lighting is prevented from entering the electrode sealing portion. Therefore, there is an effect that the luminous flux maintenance rate during lighting can be improved without using a conventional electrode coil or a heat retaining body.

[Brief description of drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Arc tube 1a Internal of arc tube 1b Sealing part of arc tube 2 Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Ikeda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd.

Claims (1)

[Claims] 1. A metal halide lamp having a lamp power of 50 W or less, containing 0.1 to 2.0 mg of mercury, 0.01 to 1.0 mg of sodium iodide, scandium iodide and iodine. One or more selected from the group consisting of cadmium iodide, indium iodide, cesium iodide, neodymium iodide, europium iodide, dysprosium iodide, holmium iodide, thulium iodide, thallium iodide and thorium iodide; A mixture of two or more kinds, and an arc tube made of quartz glass in which a xenon gas having a pressure of 0.1 to 1.0 MPa is sealed at room temperature, and a pair of electrodes sealed at both ends of the arc tube. The electrode is made of a material containing 1.0 to 4.0% by weight of thorium oxide in tungsten, and is a cylindrical rod having a diameter of 0.2 to 0.4 mm. Metal halide lamp.