JP2000277053A - Metal halide lamp and lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal halide lamp capable of suppressing the crack of an airtight container caused by a difference in the thermal expansion coefficient between electrodes, external conductors and the airtight container. SOLUTION: This metal halide lamp is provided with an airtight container 11, a pair electrodes 14, 15 sealed in the airtight container 11, metal foils 16 connected to the electrodes 14, 15 and sealed in the airtight container 11, external conductors 16 connected to the metal foils 16 and sealed in the airtight container 11 at one end, and a discharge medium containing a first halide, a second halide and rare gas and sealed in the airtight container 11. Tungsten powder with the grain size of 0.020-0.070 μm is stuck at least to the surfaces of the electrodes 14, 15 within the electrodes 14, 15 and the external conductors 17.

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 lighting device.

[0002]

2. Description of the Related Art A metal halide lamp in which a rare gas, a metal halide and mercury are sealed in a light-transmitting airtight container provided with electrodes is widely used for high efficiency and high color rendering.
In recent years, since environmental issues have been highlighted, metal halide lamps that do not contain mercury, which is a concern for environmental pollution as a discharge medium, are being developed.

It is conceivable that this type of lamp is frequently used, for example, as a headlight for a vehicle, but in the case of an application for an automobile, it is strongly required that the luminous flux rises quickly.

For this reason, attempts have been made to reduce the rise time of the luminous flux by supplying a current several times the normal rated current at the time of starting the metal halide lamp.

However, when an excessive current is applied at the time of starting, metal components such as electrodes and external conductors expand rapidly, and the difference in thermal expansion coefficient from that of an airtight container usually made of quartz or the like is caused. As a result, cracks occur in the sealing portion between the airtight container and these metal components, and other problems such as leakage of the airtight container have occurred.

In order to improve this problem, as disclosed in Japanese Patent Application Laid-Open No. 10-223175, a method of winding a coil as a thermal expansion buffer around an electrode, and Japanese Patent Application Laid-Open No. 10-241630 are disclosed. As shown in (1), there is known an electrode in which a spiral groove is provided to improve the fitting with quartz glass.

However, in the case of winding the former coil, a cavity in which quartz glass does not flow is formed around the coil and near the end, so that leakage of the airtight container is liable to occur. Cavities tend to occur, and further, the effect of reducing thermal expansion cannot be expected.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a metal halide lamp capable of suppressing cracks in an airtight container caused by a difference in the coefficient of thermal expansion between an electrode and an external conductor and an airtight container. And

In particular, a metal halide lamp in which mercury is not sealed has a relatively low lamp voltage, and the lamp current must be increased in order to operate at a constant lamp power.
There is a problem that the impact applied to the electrode increases,
Even in such a metal halide lamp, it is intended to effectively reduce cracks in the airtight container.

[0010]

According to a first aspect of the present invention, there is provided a metal halide lamp comprising: an airtight container; a pair of electrodes sealed in the airtight container; and a metal foil connected to the electrode and sealed in the airtight container. An outer conductor connected to the metal foil and one of which is sealed in an airtight container; a first halide, a second halide,
And a discharge medium sealed in an airtight container containing a halide and a rare gas, and a surface of the electrode and the outer conductor is coated with tungsten powder having a particle size of 0.020 to 0.070 μm. It is characterized by the following.

Therefore, the applied tungsten powder increases the fit of the tungsten powder with the airtight container, and the tungsten powder acts as a cushioning material, and causes a stress generated in the airtight container, the electrode and the external conductor due to thermal expansion. Are dispersed by the action of the points, that is, they are sealed at the points with the airtight container, so that cracks in the airtight container can be suppressed.

A metal halide lamp according to a second aspect is the one according to the first aspect, wherein the discharge medium is mercury-free, and one or more selected from the group consisting of Na, Sc, and a rare earth metal. A first halide mainly composed of various kinds of halides, Al, Fe, Z
n, Sb, Mn, Cr, Ga, Re, Mg, Co, N
It is characterized by including a second halide mainly containing a halide of one or more elements selected from the group consisting of i, Be, Ti, Zr and Hf.

In the present invention, since mercury is not sealed as a discharge medium, the lamp voltage is relatively low, and the lamp current must be increased in order to operate at a constant lamp power. However, similarly to the first aspect of the present invention, cracks in the airtight container can be effectively reduced.

According to a third aspect of the present invention, there is provided a lighting device comprising the metal halide lamp according to the first or second aspect and a lighting circuit for lighting the metal halide lamp, and has the same operation as the above-mentioned invention. Lighting device can be provided.

[0015]

FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a front view showing the structure of a metal halide lamp as shown in FIG. As shown in FIG. 1B, one end of the arc tube 2 of the metal halide lamp 1 is connected and fixed to the base 3, and the other end is connected to the base 3 via an external conductor 17. The arc tube 2 is covered with an outer tube 4 for cutting ultraviolet rays, and both ends of the outer tube 4 are fixed to the arc tube 2.

As shown in FIG. 1A, the arc tube 2 has an airtight container 11 mainly made of quartz.
Is composed of a spheroidal light emitting portion having a diameter of 6.5 mm and a length of 7.0 mm, and a pair of elongated sealing portions 13 formed at both ends of the light emitting portion 12 in the major axis direction. The pair of electrodes 14 and 15 has, for example, a diameter of 0.4 mm and a length of 8.0.
mm and is sealed in an airtight container 11. In addition, the metal foils 16 and 16 made of Mo are sealed in the sealing portions 13 and 13 of the hermetic container 2, and the electrodes 14 and
15 are connected to each other. In addition, metal foils 16, 16
Are connected to external conductors 17 made of Mo, respectively, and one of these external conductors 17
Sealed in three parts.

In the hermetic container 11, a discharge medium containing a first halide, a second halide and a rare gas and containing no mercury is sealed. The first halide is a halide of one or more elements selected from the group consisting of Na, Sc and rare earth metals, and the second halide is Al, F
e, Zn, Sb, Mn, Cr, Ga, Re, Mg, C
It is a halide of one or more elements selected from the group consisting of o, Ni, Be, Ti, Zr and Hf.

In this embodiment, as the discharge medium,
0.6I of ScI3, 4.2mg of NaI, 0.6mg of ZnI2 and 5 atm of Xe are sealed, and the rated lamp input power is designed to be 50W.

When constructing a metal halide lamp for direct current lighting, one of the electrodes 1 operating as a cathode is used.
It is preferable to form a heat insulating film made of, for example, alumina on the surface of the sealing portion 13 only on the fifth side.

That is, at the time of DC lighting, the luminescent substance in the hermetic container 11 moves to the wall of the hermetic container 11 on the cathode 15 side. The reason is that Sc, Na, etc. sealed in the hermetic container 11 are ionized and attracted to the cathode 15. Thus, the luminescent substance in the airtight container 11 is
Since the cathode 15 moves to the wall of the hermetic container 11 and the surplus luminescent substance is present on the cathode 15 side and the anode 14 has a higher electrode temperature, the temperature of the wall of the hermetic container 11 also increases. The height on the cathode 15 side is lower. This allows
The spectral characteristic with respect to the wavelength of light changes, and the color of the light emitted by the metal halide lamp 1 changes with time.

Therefore, if a heat insulating film is formed on the surface of the sealing portion 13 only on the cathode 15 side, the wall of the airtight container 11 on the cathode electrode 15 side is prevented from cooling, and light emitted from the metal halide lamp 1 is generated. It can be made not to change even with the passage of time.

The electrodes 14, 15 and the external conductor 1
Tungsten powder having a particle size of 0.020 to 0.070 micron is applied to the surfaces of Nos. 7 and 17.

That is, when the metal halide lamp is turned on, cracks and leaks occur due to stress applied to the hermetic container due to the difference in the coefficient of thermal expansion between the hermetic container and the electrode and the external conductor (particularly, the electrode that becomes hot). There is a possibility that.

Therefore, as described above, the surfaces of the electrodes 14 and 15 and the external conductors 17 and
If tungsten with a particle size of 0 micron is deposited, the electrode 1
Since the external conductors 4 and 15 and the external conductors 17 and 17 are fixed to the hermetic container 11 at points, it has been experimentally confirmed that the stress applied to the hermetic container 11 can be dispersed to suppress the occurrence of cracks. .

More specifically, a plurality of metal halide lamps according to the above embodiment and a conventional metal halide lamp having the same specifications except that no tungsten powder is adhered were manufactured. After performing start-up lighting for reducing the current to the rated current of 1.2 A for 3 minutes, turning off the light for 5 minutes, and then performing a blinking test in which the above-mentioned start-up lighting state and light-off state are repeated, the conventional example is 3000. While cracks occurred in the sealing portion and leaked within the blinking cycle of less than ten times, in the present embodiment, no cracks occurred even after approximately 20,000 blinking cycles.

FIG. 3 is a circuit diagram of a lighting device 21 according to the first embodiment of the present invention. This lighting device comprises the metal halide lamp 1 and a lighting circuit 22 for driving and driving the metal halide lamp 1. Lighting circuit 2
2, a DC power supply 23, a smoothing capacitor 24, a chopper circuit 25 for converting a DC voltage to a voltage of a predetermined value, a control circuit 26 for controlling the chopper circuit 25, a lamp voltage sensor 27 for detecting a lamp voltage, It comprises a lamp current sensor 28 for detecting the lamp current.

The control circuit 26 includes a lamp voltage sensor 27,
The chopper circuit 25 is controlled based on the detection signal of the lamp current sensor 28 to control the metal halide lamp 1 at a constant power. Immediately after lighting, a current that is at least three times the rated lamp current is supplied to the metal halide lamp 1, and control is performed such that the lamp current is reduced as time passes.

[0028]

According to the first aspect of the present invention, the tungsten powder adhered to the airtight container increases the fitting property of the airtight container, and the tungsten powder acts as a cushioning material, and the airtight container is thermally expanded. Then, the stress generated in the electrode and the external conductor is dispersed by the action of the point, that is, the sealing is performed at the point with the airtight container, so that the crack in the airtight container can be suppressed.

Further, in the metal halide lamp according to the second aspect, since mercury is not sealed as a discharge medium, the lamp voltage is relatively low, and the lamp current must be increased in order to operate at a constant lamp power. However, cracks in the airtight container can be effectively reduced as in the first aspect of the present invention.

The lighting device according to the third aspect has the same effect as the invention according to the first or second aspect.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a lighting circuit of the lighting device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal halide lamp 3 Base 4 Outer tube 11 Airtight container 13 Sealing part 14 Electrode 15 Electrode 16 Metal foil 17 External conductor

Claims (3)

[Claims] An airtight container; a pair of electrodes sealed in the airtight container; a metal foil connected to the electrode and sealed in the airtight container; one of the airtight containers connected to the metal foil. A discharge medium sealed in an airtight container containing a first halide, a second halide, and a rare gas, and a surface of the electrode and the outer conductor is provided with particles. 0.020-0.
A metal halide lamp, which is coated with a 070 micron tungsten powder. 2. A discharge medium comprising mercury-free, a first halide mainly composed of one or more halides selected from the group consisting of Na, Sc and rare earth metals; , Zn, Sb, Mn, Cr,
It contains a second halide mainly containing a halide of one or more elements selected from the group consisting of Ga, Re, Mg, Co, Ni, Be, Ti, Zr and Hf. The metal halide lamp according to claim 1, wherein 3. A lighting device comprising: the metal halide lamp according to claim 1; and a lighting circuit for lighting the metal halide lamp.