JP3554340B2 - Metal halide lamp lighting method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for lighting a metal halide lamp for a vehicle headlight or the like.
[0002]
[Prior art]
BACKGROUND ART In recent years, high-pressure discharge lamps, particularly metal halide lamps, have been widely used from outdoor lighting to indoor lighting in stores and the like, and recently, development has also been promoted as lamps for automobile headlamps.
[0003]
In such a metal halide lamp, the lamp arc tube may be lit in a horizontal direction. It is well known that in such horizontal lighting, as shown in FIG. 7, the discharge arc 8 between the electrodes 4 and 5 of the quartz arc tube 1 is curved upward in an arc shape. Such a curvature adversely affects the life characteristics such as lowering the lamp luminous flux by overheating and devitrifying the upper portion 9 of the arc tube 1 during the lamp life. In the prior art, to solve such a problem, the size of the arc tube has been increased to reduce the tube wall load at the time of lighting, and the temperature of the arc tube has been reduced.
[0004]
In FIG. 7, reference numerals 2 and 3 denote metal foils, and reference numerals 6 and 7 denote external lead wires, respectively.
[0005]
[Problems to be solved by the invention]
While the reduction of the tube wall load can suppress the devitrification phenomenon of the quartz arc tube, the vapor pressure of the metal halide enclosed in the arc tube decreases, and as a result, the lamp efficiency and the color rendering property decrease. Occurs.
[0006]
Further, in a metal halide lamp for an automobile headlamp, as described later, a high pressure xenon gas of 5 atm or more is sealed in an arc tube, and a discharge arc at the time of horizontal lighting (hereinafter, referred to as an arc curve) has a large curvature. Quartz devitrification on the upper side of the arc tube during the life is severe, and in an extreme case, a phenomenon that the upper portion of the arc tube swells is observed. Such bulging of the arc tube further increases the arc curvature, which also leads to a vicious cycle, such as accelerating the bulging of the arc tube. To solve such a problem, it is impossible to adopt a method of reducing the tube wall load of the arc tube in the related art. That is, as described later, in a metal halide lamp for an automobile headlamp, a luminous flux rising characteristic at the time of starting and an arc curvature at the time of lighting are defined as use conditions. This is because it is difficult to make these characteristic values within the specified values by delaying the rise of the light flux and increasing the degree of arc curvature.
[0007]
An object of the present invention is to provide a method for lighting a metal halide lamp which does not delay the rise of the luminous flux and suppresses bulging of an arc tube such as a metal halide lamp for automobiles which cannot be dealt with by the prior art.
[0008]
[Means for Solving the Problems]
A method for lighting a metal halide lamp according to the present invention is directed to a metal halide lamp having an arc tube in which electrodes are sealed at both ends and in which, in addition to a metal halide and mercury, xenon of 5 atm or more is enclosed as a starting auxiliary rare gas. The lamp is lit horizontally with a square wave lamp current having a crest factor exceeding 1 and not more than about 1.1 (crest factor = maximum value / effective value), and the arc curvature when lit horizontally is 0.75 mm or less. It is.
[0009]
[Action]
In the metal halide lamp used in the present invention, xenon having a high pressure of 5 atm is sealed in the arc tube in order to speed up the rise of the luminous flux immediately after the lamp is started. As a result, the vapor density in the arc tube, that is, the vapor specific gravity increases, the buoyancy of the discharge arc increases, and the arc curvature increases. That is, as shown in FIG. 2, if the inside of the arc tube 1 is approximated by a two-channel temperature model (the discharge arc and the peripheral temperature are assumed to be constant values Ta and Tw, respectively), the buoyancy Fa received by the discharge arc is expressed by the following equation. Is represented by
[0010]
Fa = πr _o ² g (ρ _w −ρ _a )
(However, r _o : radius of discharge arc, ρ _a : specific gravity of steam in discharge arc, ρ _w : specific gravity of steam around discharge arc, g: acceleration of gravity)
By encapsulating high-pressure xenon, the vapor specific gravity ρ _w around the discharge arc increases, and the buoyancy Fa increases. However, it has been found that when the metal halide lamp is operated with a square wave lamp current having a crest factor of 1.1 or less as in the present invention, the arc curvature is reduced. Regarding the lamp life characteristics, it was found that the quartz devitrification phenomenon on the upper side of the arc tube at the time of horizontal lighting was also slight, and that the swelling of the arc tube could be completely prevented. Since this is a low peak current value even effective current values are the same in the square wave lamp current, discharge arc temperature Ta is effectively reduced, as a result, the discharge arc vapor density [rho _a is smaller buoyancy Fa to increase Because it becomes.
[0011]
【Example】
FIG. 1 is a sectional view of an arc tube of a metal halide lamp used in the method of the present invention.
[0012]
In FIG. 1, tungsten electrodes 4 and 5 are sealed at both ends of a quartz arc tube 1 via metal foils 2 and 3 such as molybdenum foil. Further, external lead wires 6 and 7 are welded to outer ends of the metal foils 2 and 3, respectively. In the arc tube 1, iodides such as sodium and scandium as luminous substances and mercury as a buffer gas are enclosed. Further, high-pressure xenon is sealed in the arc tube 1 as a starting rare gas in order to speed up the rise of the luminous flux immediately after starting. The amount of enclosed mercury is 0.70 mg. The dimensions of the arc tube 1 are such that the inner diameter at the center is 3.1 mm, the distance between the electrodes is 4.3 mm, and the inner volume of the tube is 0.03 cm ³ .
[0013]
In the above-mentioned arc tube, an arc tube in which the sealing pressure of xenon is variously changed from 1 atm to 15 atm is prepared, and each arc tube is horizontally lit by a lamp current (square wave, trapezoidal wave, sine wave, triangular wave) having a different crest factor. The arc curvature (defined by the distance d _O from the center line connecting the tip portions of both electrodes to the center axis of the discharge arc 8) was measured. In addition, the measurement was performed with the arc tube at a constant tube input of 35 W, and the arc curvature (distance d _O ) was measured by magnifying and projecting the arc tube on a screen. As a result of the measurement, the following became clear.
[0014]
(1) FIG. 3 shows the result of lighting a lamp in which the sealing pressure of xenon was changed with a triangular wave current. As the gas pressure of xenon increases, the degree of arc curvature increases, especially at 5 atm and above. When the metal halide lamp according to the present invention is used as a headlight for an automobile, the xenon sealing pressure needs to be 5 atm or more from the viewpoint of the rise of the luminous flux immediately after starting. In addition, in combination with a reflecting mirror, it is desirable to suppress the distance d _O as an arc curvature degree to 0.75 mm or less. The arc degree of curvature increases as the xenon filling pressure increases because the vapor specific gravity ρ _W around the discharge arc increases and the buoyancy Fa received by the discharge arc region increases.
[0015]
(2) On the other hand, FIG. 4 shows the result of lighting with current waveforms having different crest factors (frequency is constant at 400 Hz). 5A shows a square wave, FIG. 5B shows a trapezoidal wave, FIG. 5C shows a sine wave, and FIG. 5D shows a triangular wave. As the crest factor decreases and the current approaches a square wave, the curvature of the discharge arc decreases. This is because the peak value of the effective value also the lamp current equal to the lamp current with decreasing the crest factor is low, the discharge arc temperature effectively steam gravity [rho _a arc region is increased to decrease, as a result, This is because the buoyancy Fa applied to the discharge arc region decreases.
[0016]
As is clear from FIG. 4, when the crest factor is 1.1 or less, the rate of decrease in the degree of arc curvature increases.
[0017]
Next, using a luminous tube filled with 10 atm of xenon, observe the lamp life characteristics when horizontally lit with lamp currents with different crest factors (frequency 400 Hz), that is, observe the quartz devitrification state and the bulging phenomenon of the luminous tube on the upper side of the luminous tube. did. In the lighting cycle, a cycle of lighting for 9 minutes and 45 seconds / light-off for 15 seconds was repeated five times, and then light-off was performed for 10 minutes. Thereafter, the cycle for 60 minutes was repeated. The result at a life time of 2000 hours is shown in FIG. It is apparent from this that the bulging of the arc tube is significantly reduced when the crest factor is 1.1 or less.
[0018]
The above measurement was performed in a low frequency region of 12 KHz or less as a lighting frequency in order to avoid an acoustic resonance phenomenon in the arc tube. In particular, in the measurement of the life characteristics, the lamp was turned on at 400 Hz. In the frequency range of the measurement of 12 KHz or less, the dependence of the arc curvature on the lighting frequency is small, and it can be said that there is no problem.
[0019]
Further, the luminous flux rising characteristics depended on the size of the arc tube, and there was no difference due to the crest factor of the lamp current, and no delay in luminous flux rising was observed.
[0020]
【The invention's effect】
As described above, according to the present invention, in a metal halide lamp in which high-pressure xenon is sealed as a starting rare gas, the crest factor is 1 even in a lamp in which the xenon sealing pressure is 5 atm or more and the arc curvature during horizontal operation is increased. beyond horizontally turned about 1.1 or less square-wave lamp current, by arc curvature when the horizontal lighting is less than 0.75 mm, without delaying the rising light beam, yet with reduced arc curvature Further, it is possible to provide a metal halide lamp in which the bulging of the arc tube is suppressed and the life characteristics are remarkably improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an arc tube of a metal halide lamp used in the method of the present invention. FIG. 2 is a diagram for explaining buoyancy of a discharge arc region in the arc tube. FIG. 3 is a relationship between xenon sealing pressure and arc curvature. FIG. 4 is a diagram showing the relationship between crest factor and arc curvature. FIG. 5 is a waveform diagram of a square wave, FIG. 5B is a waveform diagram of a trapezoidal wave, FIG. 5C is a waveform diagram of a sine wave, and FIG. FIG. 6 is a diagram showing the relationship between crest factor and bulging of the arc tube. FIG. 7 is a diagram for explaining the curvature of a discharge arc in the arc tube.
1 arc tube 4,5 electrode

Claims (1)

Electrodes are sealed at both ends, and a metal halide lamp equipped with an arc tube in which xenon with a filling pressure of 5 atm or more is filled as a starting rare gas, in addition to metal halide and mercury, has a crest factor of 1. Yue example 1. A method for lighting a metal halide lamp, wherein the lamp is horizontally lit with a square wave lamp current of 1 or less, and the arc curvature at the time of horizontal lighting is 0.75 mm or less.

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