JPH0582086A - Metal halide lamp - Google Patents

Abstract

PURPOSE:To provide a metal halide lamp, with which risk of arc swings or stall is prevented, W attachment to the tip of the electrode is precluded, and the root of an electrode shaft is prevented from breakage. CONSTITUTION:An electrode 3 is installed sealedly at the end of the bulb 1 of a light emitting tube, and iodide and bromide of rare earth metal and also mercury and ware gas are encapsulated in this bulb. In this metal halide lamp, the electrode shaft 4 has a separated tip part 41 and root part 42, which are coupled together by an electrode coil 5, and the dia. d1 of the tip part is made smaller than the dia d2 of the root part. Smaller dia. of the tip part stabilizes the position where a bright point is generated in the arc and prevents generation of arc swings or stall, and thicker root of the electrode shaft precludes risk of breakage even in the occurrence of thinning and also prolongs the lifetime.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small metal halide lamp, and more particularly to improvement of life characteristics.

[0002]

2. Description of the Related Art Since metal halide lamps are discharge lamps with high efficiency and high color rendering properties, they have been conventionally used for wide area lighting such as roads, open spaces, stadiums, etc. It is also being used in floodlights such as projectors.

With the spread of such spread, this kind of lamp has come to be used in combination with a device such as a reflecting mirror, and therefore, this kind of lamp as a light source makes it easier to control light. It is desired to be close to a point light source. Therefore, this type of metal halide lamp is being shortened, that is, downsized. However, downsizing the lamp generally increases the tube wall load and tends to increase the temperature of the arc tube.

On the other hand, this type of lamp uses S as a luminescent metal in order to obtain higher efficiency and color rendering.
It has been devised to encapsulate rare earth metals such as c, Dy, Tm, and Ho as halides such as iodine I and bromine Br.

However, in such a small metal halide lamp using a halide of a rare earth metal, blackening easily occurs on the tube wall at an early stage. In other words, especially when using iodine as the halogen, the lamp filled, for example, ScI ₃ as a light-emitting metal, quartz (SiO ₂₎ of the arc tube material and the ScI ₃ reacts, SiI ₄ and Sc ₂
Generates O ₃ . This reaction is more likely to occur as the tube wall load is higher and the arc tube temperature is higher, and thus is more likely to occur in the small metal halide lamp.

When SiI ₄ is generated by the above reaction, it adheres to the tip of the electrode and forms a low melting point alloy of tungsten W and silicon Si with tungsten W which constitutes the electrode. Since this alloy has a low melting point, it is subjected to electron impact and scattered from the tip of the electrode. The scattered low-melting-point metal adheres to the inner surface of the bulb and is blackened to absorb visible light, thereby lowering the luminous flux maintenance factor.

When SiI ₄ adheres to the tip of the electrode to form a low melting point alloy with tungsten W and when the low melting point alloy is scattered, the tip of the electrode is corroded and the shape is deformed, resulting in an arc spot. It may also cause instability in the occurrence position of.

In order to prevent such a problem, when bromine Br is mixed in addition to iodine I as a halogen, bromine is combined with tungsten W adhering to the tube wall and tungsten of the low melting point alloy of silicon Si to form an electrode. It has been found that the tube wall is purified, the blackening of the tube wall is prevented, and the luminous flux maintenance factor is improved.

[0009]

However, in this case, when the temperature of the electrode tip is high, the tungsten W returned from the tube wall tries to adhere to the high temperature portion and is deposited on the electrode tip, which gradually grows. As a result, the tips of the electrodes grow more and more, and the distance L between the electrodes is shortened, resulting in a large variation in the lamp characteristics. The temperature of the electrode tip is determined by the lamp current and the diameter of the electrode shaft. If the lamp current is constant, the smaller the diameter of the electrode shaft, the higher the temperature of the electrode tip.

Therefore, in order to prevent the tungsten W from adhering to the tip of the electrode and prevent the development of the adhered tungsten W, the electrode shaft may be thickened to lower the temperature of the electrode tip.

However, if the tip of the electrode shaft is enlarged, the temperature of the entire tip is lowered, but the point where the arc spot is generated is not fixed, and since the arc spot of this type of lamp is thin, the large surface of the tip of the electrode shaft can be scattered around. It moves, thus causing an arc swing and easily disappearing.

Further, as described above, when bromine Br combines with tungsten in the low melting point alloy of tungsten W and silicon Si and returns to the high temperature portion of the electrode tip, the temperature of tungsten is relatively low. It comes to be supplied from the base of the electrode shaft. That is, tungsten at the base of the electrode shaft forms a low melting point alloy of W and Si with SiI _4, and tungsten W of this low melting point alloy is attached to the high temperature part of the electrode tip by the action of bromine Br. Is transported from the base of the electrode shaft having a low temperature to the high temperature portion of the electrode tip and is deposited on the electrode tip. For this reason, the electrode is thinned at the base of the electrode shaft, and the electrode shaft is broken. Therefore, it is desired that the base of the electrode shaft be thick.

The present invention has been made in view of the above circumstances. An object of the present invention is to prevent tungsten W from adhering to the electrode tip without causing arc shaking and extinguishing, and to prevent the electrode shaft. An object of the present invention is to provide a metal halide lamp that prevents breakage of the root and has improved life characteristics.

[0014]

In order to achieve the above-mentioned object, the present invention encloses an electrode at the end of an arc tube bulb, in which iodide and bromide of rare earth metal, mercury, and a rare gas are contained. In a metal halide lamp in which a gas is enclosed and the electrode is formed by winding an electrode coil around the tip of the electrode shaft, the electrode shaft separates the tip and the root, and the tip and the root are separated by an electrode coil. It is characterized in that the diameter d _{1 of the} tip portion is smaller than the diameter d _{2 of the} root portion while being connected.

[0015]

According to the present invention, the electrode shaft is separated into the tip portion and the root portion, and the diameter d _{1 of the} tip portion is made smaller than the diameter d _{2 of the} root portion, so that the arc bright spot generation position is stable. Then, the occurrence of arc shaking and extinction is prevented, and since the electrode shaft root is thick, it is less likely to break even if thinning occurs, and moreover, by forming the diameter of the root part of the electrode shaft as a whole larger than before, It is possible to reduce the temperature rise of the entire electrode and prevent tungsten W from adhering to the tip of the electrode.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

The drawing shows a small metal halide lamp with a rated output of 2 KW, and 1 is an arc tube bulb, which is made of transparent quartz glass. The valve 1 has a substantially elliptical shape, for example, an inner diameter of 40 mm in the major axis direction and an inner diameter of about 36 mm in the minor axis direction.

Sealing tubes 2 and 2 are joined to both ends of the valve 1, respectively. These sealing tubes 2 and 2 are made of translucent quartz glass or hard glass, and are fused to both ends of the bulb 1.

The sealing tubes 2 and 2 are sealed with electrodes 3 and 3. The electrodes 3 and 3 are configured by attaching an electrode coil 5 to the tip of an electrode shaft 4 described later. These electrodes 3 and 3 are exposed in the bulb 1, and the tips of the electrode shafts 4 and 4 are opposed to each other in the bulb 1 with a predetermined interelectrode distance L, for example, 30 mm.

The base end portion of the electrode shaft 5 is welded to a first metal foil conductor 6 such as molybdenum, and the first metal foil conductor 6 is joined to an intermediate lead wire 7 made of molybdenum or the like. There is. The intermediate lead wire 7 is welded to a second metal foil conductor 8 made of molybdenum or the like, and the second metal foil conductor 8 is joined to an outer lead wire 9 made of molybdenum or the like.

The one metal foil conductor 6, the intermediate lead wire 7, the second metal foil conductor 8 and the outer lead wire 9 as described above are crushed in the above sealing tubes 2 and 2. By sealing, it is hermetically sealed. The external lead wires 9, 9 are connected to a cap (not shown) attached to the ends of the sealing tubes 2, 2.

The structure of the electrode 3 is shown in FIG. 3B. To explain this, the electrode shaft 4 is divided into a tip portion 41 and a root portion 42, and the tip portion 41 and the root portion are separated from each other. The portion 42 is mechanically coupled by the electrode coil 5 wound so as to extend over these portions, and is electrically connected. The tip portion 41 of the electrode shaft 4 is made of tungsten W (tritan) containing thoria (ThO ₂ ), and has an outer diameter d ₁ of 2.
It is formed to have a thickness of about 3 to 2.5 mm.

The base portion 42 of the electrode shaft 4 is made of Thor (ThO).
₂ ) Pure Tungsten W that does not contain, or Doped Tungsten that contains an oxide such as K or Al,
The outer diameter d ₂ is always larger than the diameter d ₁ of the tip portion 41 (d ₁
<D ₂ ), for example, about 2.5 to 3.0 mm. The electrode coil 5 is made of tungsten W (tritan) containing thoria (ThO ₂ ) and has a wire diameter of 1.5 to
It is wound 6 to 7 times with a length of about 2.0 mm. The arc tube bulb 1 is filled with a rare earth metal halide and a rare gas such as mercury and argon.

The rare earth metal halide is, for example, Dy.
Br₃Is 4 mg, HoBr₃Is 4 mg, TmBr₃Is 4 mg,
HgBr₂10 mg, CsI 12 mg, HgI₂Is 3 mg
It is said that. Mercury Hg is 100 mg and argon is
Enclosed in 100 Torr. And this Metal Harai
When the lamp is lit at 2kW, the lamp current I_LBut
It becomes 19.0 amps. Therefore, the lamp current I_LAnd electric
Diameter d of the tip 41 of the polar axis 4₁The relationship with₁ ² = 0.28I_L  Has become. Metal halide lamp with such a configuration
The operation will be described.

The electrode shaft 4 of the above embodiment has a diameter d of the root portion 42.
₂ is formed to be, for example, about 2.5 to 3.0 mm and is larger than the diameter (about 2.0 mm) of the conventional equivalent rated lamp electrode shaft, so that the temperature rise of the entire electrode is suppressed. You can

Therefore, since the temperature of the electrode tip portion 41 is also suppressed, it is attempted to combine bromine with tungsten W attached to the tube wall and tungsten of the low melting point alloy of silicon Si to deposit on the electrode tip portion 41. And prevents tungsten from gradually growing and extending at the electrode tip. For this reason, the distance L between the electrodes does not change, and fluctuations in the lamp characteristics are prevented. Further, since the deposition of tungsten on the electrode tip portion 41 is reduced, the ratio of being carried from the electrode shaft root portion 42 is reduced, and the electrode shaft is also thinned.

Since the electrode shaft 4 is divided into the tip portion 41 and the root portion 42 and the diameter d ₁ of the tip portion 41 is made thin, the arc spot generation point becomes constant and the arc swing is prevented. At the same time, there is less disappearance.

Further, since the diameter d ₂ of the root portion 42 is made thick, even if the tungsten of the root portion 42 is carried to the high temperature portion of the electrode tip and becomes thin, since it is originally thick, it takes time to break. It takes longer and has a longer life than before. An experiment was conducted to confirm the effect of the configuration of the present invention, and the results are shown in Table 1.

[0029]

[Table 1]

From the results shown in Table 1 above, in the conventional case where the electrode shaft is formed of a single shaft having the same thickness, tungsten W is deposited on the tip of the electrode, the erasing voltage is lowered and the erasing is apt to occur, and In many cases, the base of the electrode was thin.

On the other hand, as in the present invention, the tip portion 41 and the root portion 42 of the electrode shaft 4 are separated and the diameter d of the tip portion 41 is increased.
_{When 1} is made thinner than the diameter d ₂ of the root portion 42, tungsten W is less likely to be deposited on the electrode tip, arc swing is reduced, the extinguishing voltage is lowered, and the electrode root portion is less thinned. .. Therefore, it was confirmed that the lamp life was extended.

The tip portion 41 of the electrode shaft is made of thoria.
Since it was formed of the contained tungsten,
Emission action improves startability. Against this
However, the root portion 42 is made of tungsten containing no thoria.
Since it is formed, an arc spot is generated at the root portion 42.
Can be prevented. That is, the root portion 42 has a diameter d
₂The larger surface area increases the distance between the electrodes.
It is a short arc type metal halide lamp with a short separation L.
Therefore, there is concern that glow discharge may occur from the root 42.
However, the root portion 42 is made of tungsten containing no thoria.
When formed with
The emission of electrons is reduced at the root portion 42, and
It is possible to prevent the occurrence of dark spots. Also, the electrode shaft
Diameter d of tip 41₁(Mm) and lamp current I_L(Ampe
The relationship with (a) (current density) is 0.12 · I_L<D₁ ² <0.47 · I_L  The range of is desirable.

That is, d ₁ ² Is 0.12 · I _L or less, the current density becomes high, the temperature of the electrode shaft tip portion 41 rises, the amount of tungsten W deposited on the tip increases, and the inter-electrode distance L shortens. Conversely, d ₁ ² If is or 0.47 · I _L, but decreases the temperature of the whole tip, not fixed generation point of the arc spot, A - with causing click shaking,
It becomes easy to disappear.

Furthermore, when bromine Br is mixed in addition to iodine I as a halogen, as described above, bromine is combined with tungsten W adhering to the tube wall and tungsten of the low melting point alloy of silicon Si to form an electrode. A returning action is caused, so that the tube wall is purified, blackening of the tube wall is prevented, and the luminous flux maintenance factor is improved. In this case, the ratio Br / I of the bromine atom Br to the iodine atom I is preferably in the range of 1-5.

When the ratio Br / I of bromine to iodine is less than 1, the initial purpose of mixing bromine Br cannot be achieved, and there is a phenomenon that the arc becomes thick and the color temperature lowers. When Br / I exceeds 5, bromine directly reacts with the tungsten at the electrode tip and the root, adheres to the tube wall, and the luminous flux maintenance factor decreases. The present invention is not limited to the above embodiment. That is, the tip portion 41 and the root portion 42 of the electrode shaft 4 may be in contact with each other if they have different diameters, or may be integrally molded.

[0036]

As described above, according to the present invention, the electrode shaft is separated into the tip portion and the root portion, and the diameter d _{1 of the} tip portion is made smaller than the diameter d _{2 of the} root portion. The bright spot generation position is stable and prevents arc shake and extinction.Because the base of the electrode shaft is thick, it is less likely to break even if thinning occurs, and the diameter of the base of the electrode shaft as a whole is conventional. By making it larger, it is possible to reduce the temperature rise of the entire electrode and prevent tungsten W from adhering to the tip of the electrode. For this reason, the lamp characteristic does not fluctuate over a long period of time, the electrode shaft can be prevented from being broken, and the life is extended.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, (A) is a sectional view of a metal halide lamp, and (B) is a sectional view showing a structure of an electrode thereof.

[Explanation of symbols]

1 ... Valve, 2 ... Sealing tube, 3 ... Electrode, 4 ... Electrode shaft, 5 ...
Electrode coil, 6, 8 ... Metal foil conductor, 7 ... Intermediate lead wire,
9 ... External lead wire, 41 ... Tip of electrode shaft, 42 ... Root of electrode shaft.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Ito Inventor Hideki Ito 4-28, Mita, Minato-ku, Tokyo Inside Toshiba Lighting & Technology Corporation

Claims (3)

[Claims] 1. An electrode is sealed at the end of an arc tube bulb, and a rare earth metal iodide and bromide, mercury, and a rare gas are sealed in the bulb, and the electrode has an electrode coil at the tip of an electrode shaft. In a metal halide lamp constructed by winding, the electrode shaft separates a tip portion and a root portion, and the tip portion and the root portion are connected by an electrode coil, and a diameter d _{1 of the} tip portion is changed to a diameter d of the root portion. A metal halide lamp characterized by being smaller than ₂ . 2. The metal halide lamp according to claim 1, wherein a tip portion of the electrode shaft is made of tungsten containing thorium, and a root portion thereof is made of tungsten containing no thorium. 3. The diameter d of the tip of the electrode shaft₁(Mm) is
The lamp current is I_L0.12 · I_L<D₁ ² <0.47 · I_L  The method according to claim 1 or claim 2, wherein
Metal halide lamp.