JPS6222221B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a metal halide lamp, and its efficiency and light color unevenness are improved. A metal halide is selected and sealed in the arc tube of a metal halide lamp so as to produce white light with high efficiency. Metal halides are often sealed in excess of the amount that evaporates to reach the saturated vapor pressure during lamp operation.
The unevaporated metal halide becomes a liquid and condenses at the lowest or lowest temperature part of the arc tube. When lighting vertically, it condenses at the rear of the lower electrode of a normal arc tube. As a result, the metal halide is not exposed to high temperatures and sufficient vapor pressure cannot be obtained, resulting in a decrease in efficiency, and differences in vapor pressure between lamps occur due to variations in temperature at the rear of the electrode, resulting in light color. Causes unevenness. In order to eliminate this inconvenience, heat insulating means such as providing a metal oxide film on the outer wall of the arc tube around the electrode or surrounding it with a metal cap have been conventionally used, but these measures have not been sufficient. The arc tube is housed in an outer tube, and a protective gas is sealed inside the outer tube.
When a metal halide lamp is lit, the temperature of the protective gas inside the outer bulb increases due to heat conduction from the arc tube, causing convection. In other words, the high-temperature protective gas that touches the wall of the arc tube moves upward, touches the inner wall of the outer tube, lowers its temperature, moves downward, and then touches the arc tube again, creating a convection current that increases the temperature. wake up However, when the protective gas that has been cooled by contacting the inner wall of the outer tube due to convection comes into contact with the wall of the arc tube again, it cools the vicinity of the outer wall around the lower electrode of the arc tube. With conventional metal oxide films and metal caps as mentioned above,
It is susceptible to the cooling effect of this convection and is not sufficient as a heat retention means. In addition, as a measure against the cooling effect of the outer wall around the lower electrode of the arc tube due to convection, the present inventor previously proposed the following:
We proposed that a translucent heat shielding plate, such as a mica plate, be placed in the sealing part of the arc tube, which is the lower side when the lamp is lit.
However, the heat resistance temperature of mica board is 550 to 750℃.
At higher temperatures, crystallization water begins to decompose, releasing moisture and becoming brittle. Due to the release of moisture, the starting voltage of the metal halide lamp increases,
Furthermore, the mica plate becomes brittle and becomes difficult to fix to the sealing portion. For this reason, it is possible to use mica board as a translucent heat shielding plate in low-wattage metal halide lamps of around 100W, but
When it exceeds 400W or 1000W, it becomes difficult to use because the heat resistance is insufficient. Further, heat-resistant glass is difficult to securely hold in the sealing portion and does not have sufficient mechanical strength. The present invention has been made in view of the above-mentioned disadvantages, and it is an object of the present invention to provide a metal halide lamp that can sufficiently improve efficiency and light color unevenness. An embodiment of the present invention will be described below with reference to the drawings. In the figure, inside the arc tube 1 is sodium,
A halide such as thallium or indium is sealed, and electrodes 2 and 3 are sealed at both ends. Both electrodes are electrically connected to stem wires 4 and 5, respectively. Stem wire 5 approaching arc tube 1
is covered with an insulating protective tube 6 such as an insulator tube or a quartz tube to prevent sodium from disappearing outside the arc tube due to well-known photoelectron emission. Lower electrode 3
A heat insulating film 7 is applied to the wall of the arc tube around the arc tube 1, and of the sealing parts formed at both ends of the arc tube 1, the lower sealing part when lit, that is, the lower electrode is sealed. A metal heat shielding plate 9, for example, a disc made of nickel, stainless steel, etc., is inserted into the insulating protective tube 6 through a tab 10 formed by cutting and cutting a metal heat shielding plate 9 into the sealing portion 8 in a direction substantially perpendicular to the arc tube axis. It is welded to the attached clasp 11. The metal heat shielding plate 9 has a width D (mm) at its longest part of 1 to 2.5 d, where d (mm) is the outer diameter of the arc tube 1 .
The arc tube 1 is provided within an outer tube (not shown) filled with a protective gas such as nitrogen, neon-nitrogen, or other inert gas. A metal halide lamp with such a configuration has a D/d
A metal heat shielding plate whose temperature is within the above range is installed in the sealing part 8 of the arc tube 1, which is on the lower side during lighting, in a direction almost perpendicular to the tube axis of the arc tube. Without blocking the light, without being adversely affected by the cooling effect of the wall of the arc tube 1 around the lower electrode 3 due to the convection of the protective gas inside the outer tube, the heat retention effect is significantly improved.
Efficiency and light color unevenness can be improved. Furthermore, since the metal heat shielding plate 9 is in an electrically free state, the inclusions in the arc tube 1 are not electrically attracted by photoelectrons or potential difference, and the composition of the inclusions is always stable and the arc is generated. Stabilize. Experiments have shown that the relationship between the longest width D (mm) of the metal heat shield plate and the outer diameter d (mm) of the arc tube is important for improving the efficiency and light color unevenness of the metal halide lamp. Ta. In other words, the outer diameter of the arc tube is 21.5 mm, and the distance between electrodes is 41 mm.
For a 400W metal halide lamp with the structure shown in which sodium, thallium, and indium iodides are sealed in an arc tube whose end outer wall is coated with a graphite heat-retaining film, a disk-shaped nickel plate is used as the metal heat shield. When the outer diameter of this nickel plate was varied and the effects on efficiency, light color unevenness, etc. were investigated, the results shown in Table 1 were obtained.
In addition, the unevenness of light color is evaluated by the variation in color temperature, and the presence or absence of shadows due to the metal heat shield plate is evaluated based on the lamp itself.
The illuminance of a circular irradiation surface with a diameter of 1 m was measured directly below the irradiation surface, and the evaluation was made by comparing the relative value of the illuminance when the case without a metal shielding plate was set as 100.

[Table] As shown in Table 1, Sample 1 had almost no difference in various properties such as efficiency compared to the sample without the disk (Sample 6), and there was no improvement effect. In sample 2, the efficiency increased to 85 lm/W, the variation in color temperature decreased to 4000 to 4600 K, the relative illuminance value was 102, and there was no shadow. For samples 3 and 4, the efficiency increased to 84.5lm/W, the color temperature variation was further reduced to 4000-4500K, and the relative illuminance values were 99 and 98, respectively.
However, the presence of the shadow was almost invisible. In sample 5, the color temperature was improved from 4000 to 4500K, but the efficiency decreased to 79 lm/W, and the relative illuminance value also became 90, so that shadows were clearly visible. Furthermore, even when used in combination with a floodlight, shadows could not be eliminated. Further, similar results were obtained when an experiment was conducted by changing D/d with an arc tube outer diameter of 18.5 mm and an electrode distance of 60 mm. Furthermore, the metal heat shielding plate may be polygonal, such as hexagonal or octagonal, other than circular. In addition, if a metal heat shield plate is installed at a position away from the arc tube, as in the case of reflective mercury lamps, which is used to reduce the heat at the top of the reflective glass tube, the efficiency and light color will be reduced. It was not possible to improve unevenness, etc. The metal halide lamp proposed in Japanese Patent Publication No. 41-2865 has a reflective shielding plate in combination with a glass tube surrounding the arc tube to keep the arc tube warm. The purpose is completely different from that of the invention, which prevents the cooling effect of the lower end of the arc tube by convection. In addition, in this structure, the reflective shielding plate is not electrically isolated and a potential is always applied to it, so that the inclusions in the arc tube are attracted by photoelectrons and potential difference. There is an inconvenience that the light is lost outside the arc tube. As explained above, the present invention prevents cooling of the protective gas sealed in the outer bulb by convection, increases the temperature of the lowest temperature part of the arc tube, and improves efficiency without blocking light from the arc tube. It is possible to provide a metal halide lamp that can prevent light color unevenness and the like.

[Brief explanation of the drawing]

The figure is a front view of essential parts of a metal halide lamp which is an embodiment of the present invention. 1... Arc tube, 2, 3... Electrode, 8... Sealing part, 9... Metal heat shielding plate.

Claims (1)

[Claims] 1. An arc tube equipped with electrodes at both ends and a metal halide sealed inside, an outer tube containing the arc tube and filled with a protective gas, and a seal formed at both ends of the arc tube. Only the sealed portion of the arc tube, which is on the lower side when lit, is provided with a metal heat shield plate that is disposed in an electrically free state in a direction substantially perpendicular to the tube axis of the arc tube, and the metal heat shield Width at the longest part of the board D
(mm) and the outer diameter of the arc tube is d (mm), the ratio D/d of D and d is 1 to 2.5.