JPS601746A - Metal vapor discharge lamp - Google Patents

Abstract

PURPOSE:To prevent missing of transparency and occurrence of crack even when firing through power source having no cathode inversion by coating the sealed end of cathode made by winding a coil over the electrode shaft with insulator. CONSTITUTION:Anode 3 and cathode 4 are connected through molybdenum foils 7a, 7b to be sealed air-tightly in sealed sections at the opposite ends of a light emission bulb to the external lead wires 8a, 8b to form a light emission tube 1. Said tube 1 is sealed in an outer tube to form a lamp which is fired through power source having no polarity inversion such as an inverter. In such a metal vapor discharge lamp, cathode 4 is formed by winding a coil 4b over a portion of an electrode shaft 4a while the surface of the electrode shaft 4a is coated with insulator 5 over the range longer than (l-d) from the sealed end, assuming the outer diameter of the coil 4b is dmm. while the length of the electrode shaft 4a from the cathode sealed end to the lower end of coil is lmm..

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a metal vapor discharge lamp that is operated using a power source with no polarity reversal, such as direct current.

(Technical background of the invention and its problems) In recent years, highly efficient metal vapor discharge lamps such as metal halide lamps and high-pressure sodium lamps have been widely used from the viewpoint of energy conservation.

These metal vapor discharge lamps operate at a commercial frequency of 50Hz or 60Hz.
It was customary to use a general power supply of 100 V or 200 Hz AC via a ballast to light the lamp. When these metal vapor discharge lamps are lit with an AC power source whose polarity reverses in a certain cycle, the pair of electrodes in the two arc tubes alternately serve as cathode and anode, and at this polarity change momentarily, the power source There is a current stop period when the voltage is zero. Therefore, the electrodes of AC metal vapor discharge lamps must have both the performance as an anode that can withstand the bombardment of accelerated ions, and the performance as a cathode, which requires excellent electron emissivity. is necessary.

The anode has contradictory properties, such that a larger electrode structure is suitable, while the cathode has a smaller electrode structure.9 Electrode designs are being carried out that strike a compromise between the two. Therefore, this was not necessarily a preferable form from the viewpoint of the original discharge stability of 9. Furthermore, as mentioned above, when the polarity is reversed, there is a point where the voltage becomes zero, and there is a current stop period where the discharge current becomes zero, and this is when the voltage value is sufficient to cause the discharge to occur. The longer this period is, the higher the voltage required for the next discharge will be. This high voltage value at the time of polarity reversal in each half cycle is called the restriking voltage, and this restriking voltage always occurs when AC lighting is performed with polarity reversal, and this is due to factors such as turn-off voltage and life characteristics. It is known to have a significant effect on lamp characteristics.

For these reasons, methods of lighting using a power source that does not have polarity reversal, such as direct current lighting instead of alternating current, are attracting attention. There were obstacles such as the inverter and other circuits needed to convert the power supply to a non-converting power source to be too large, and the need to develop electronic components for large currents, making it impossible to put it into practical use except for special purposes. Recently, resource saving.

From the perspective of energy conservation, there is a strong demand for the development of highly efficient compact metal vapor discharge lamps to replace the inefficient incandescent bulbs used in general households, and the performance of electronic components is also improving day by day. In view of the current situation, it is becoming urgent to review metal vapor discharge lamps that are lit using a power source that does not have polarity reversal.

In the process of developing a metal vapor discharge lamp that uses a DC or rectified power source, the inventors discovered an important problem that did not occur with conventional AC lighting. This is because metal vapor discharge lamps operated using a power source that does not have polarity reversal often develop cracks in the wall of the arc tube near the cathode, causing leaks from the two arc tubes and causing many lamps to fail. Moreover, it has been found that this phenomenon becomes even more severe in small lamps in which the cathode and the wall of the arc tube are closer together. We further observed these phenomena by comparing them with AC lamps.
It has been found that even if the lamp is stable in steady state, if the lamp is lit with a power supply that frequently reverses polarity, an arc spot will be formed on the sealed end of the cathode, and this spot may not migrate to the tip of the cathode. It was found that most of the lamps that were left on for several hours in this state caused racking as described above. On the other hand, in the case of AC lighting, although discharge started from the sealed end side of the electrode immediately after starting, the arc spot moved to the electrode tip in all lamps in a short time, and no cracks occurred.

This phenomenon is presumed to be due to the following reasons. That is, even in the case of an alternating current power source with no polarity reversal, the discharge starts with a long discharge distance because the pressure is low at 1 atm or less immediately after startup. However, as the temperature inside the arc tube increases over the course of one hour, the pressure inside the arc tube rises and reaches a high pressure of 1 atm or more during rated lighting, for example, around 10 atm or more in the case of a metal halide lamp.

Therefore, in order to maintain stable discharge, the arc spot moves from the electrode sealing end to the electrode tip so as to satisfy the well-known law Pd = const, (P is pressure, d is discharge distance). It moves in the direction where the discharge distance d becomes shorter. This phenomenon is caused by the fact that in the case of alternating current, each electrode acts as both a cathode and an anode in each half cycle, so when it is an anode, the arc concentrates over the entire area of the electrode and the tip of the electrode is also heated. As the current increases, the arc easily moves to the tip of the electrode, but when there is no reversal of polarity, such as with direct current, the arc becomes a spot on the cathode side and concentrates only on a small part of the electrode. Although the temperature rises only in the concentrated area, immediately after starting, the temperature at the electrode tip does not rise to a level sufficient for electron emission even if the pressure inside the arc tube increases sufficiently since the electrode is on the sealed end side. Since there is no reversal of polarity, it is inferred that the movement of the arc from the spot position once created may not occur unless there is some trigger. In an effort to shorten the distance.

Another point is that emissions are generated from locations with good electron radiation.

For example, if the temperature gradient between the electrode tip on the cathode side and the area where the arc spot occurs is small and the electrode tip also has a sufficiently high humidity, the arc will easily move to the electrode tip as the pressure inside the tube increases. It just so happens that there is a spot with particularly good emission on the electrode sealing end side, and the discharge starts from that spot.

When the altitude gradient with the electrode tip was large, the arc did not move to the electrode tip and continued to maintain discharge on the sealed end side until the end. The type with a coil wound around the electrode shaft has a thick altitude gradient, and in order to reduce the gradient, the starting characteristics have to be sacrificed.

In this case, areas with particularly good emission are, for example, cases where a metal or metal compound sealed in the arc tube with good emission adheres to the vicinity of the sealed end of the electrode, or an arc spot is formed from the same place many times. This is thought to be due to the fact that if the air continues to be emitted, it becomes easier for that area to emit emissions than other areas.

[Object of the Invention] An object of the present invention is to provide a long-life metal vapor discharge lamp that does not cause devitrification or cracks in the arc tube even when lit with a power source that does not have polarity reversal, such as direct current lighting.

[Summary of the invention]

In the present invention, the sealed end side of the electrode shaft of a cathode formed by winding a coil around the electrode shaft is coated with an insulating material, thereby preventing the formation of an arc spot at that portion.

This prevents the occurrence of cracks in the arc tube near the electrodes.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to the illustrated embodiments. Figure 1 shows the arc tube (1) of a 40W small metal halide lamp.The arc tube pulp (2) is made of quartz glass and is formed into an almost spherical shape with an inner diameter of approximately 8 tax. 100 torr, mercury 10
mg and a metal halide such as scandium iodide and sodium iodide are sealed in a heavy weight ratio of 1:5, and an anode (3) is placed at both ends of the 9 arc tube pulp (2) facing each other. and cathode (4
) are sealed. The anode (3) has a diameter of approximately 0.22 m.
The electrode axis is a tungsten rod with a diameter of approximately 0.06 mm.
A tungsten wire having a diameter of approximately 0.18 mm is roughly wound around a tungsten core wire, and then tightly wound around the electrode shaft to form an electrode coil portion having a length of approximately 1.5 mm.

On the other hand, the cathode (4) uses a tungsten rod (4a) with a diameter of about 0.121111 as the electrode shaft (4a), and a tungsten wire with a diameter of about 0.031 m with a diameter of about 0.06! A coil (4b) having a length of about 1 mm is formed by coarsely winding an In tungsten core wire and tightly winding it around the electrode shaft (4a). Both electrodes (3
) and (4) both have a protrusion length in the arc tube of about 2 degrees. Further, most of the length l) from the sealed end of the electrode shaft (4a) of the cathode (4) to the lower end of the coil (4b) is covered with an insulator (5) such as a quartz tube. covered with.

Furthermore, the anode (3) and cathode (4) are connected to external leads through molybdenum foils (7a) and (7b) that are hermetically sealed within the sealing parts (6a) and (6b) at both ends of the arc tube pulp. Line (8a).

(8b) are connected to each other to form an arc tube (1). This arc tube (1) is sealed in an outer tube with a cap attached to one end (not shown), and the external lead wire (8a)
, (sb) are connected to the base and the terminal to form a lamp. Such a lamp (indicated by a dotted line) is powered by a lighting device as shown in Figure 2, for example, through an inverter that converts a general commercial frequency AC power source (9) into a DC power source with no polarity reversal.

A voltage is applied to both ends of the arc tube (1) via a ballast connected in series with the lamp to control the current.

It will be lit.

Next, the above example lamp and the electrode shaft (4a) of the cathode (4)
We manufactured 30 lamps each with the same rating (comparison product) that have arc tubes that are not covered with any insulating material, and then divided them into half of each, 15 lamps, and lit them vertically using the above lighting device (with the arc tubes positioned vertically). ) and horizontal lighting (the arc tube position is horizontal), ON and OFF flashing tests were conducted, and the position of the arc spot, devitrification of the arc tube near the cathode, crack occurrence, etc. were observed. . As a result, in the example, no devitrification or cracking occurred even after 1000 flashes in both vertical and horizontal lighting, and no arc spots were generated on the root side (sealed end side) of the cathode electrode axis. Ta. On the other hand, the rate of occurrence of devitrification and cracks in the luminous tube of comparative products, that is, lamps whose electrode shafts are not covered with an insulating material, is 2/15 for the vertically lit lamp and 2/15 for the horizontally lit lamp after 1000 blinks. 15 pieces/15 pieces or 10
The rate was as high as 0%. Also.

Further detailed examination of the two defective electrodes due to vertical lighting revealed that the angle between the electrode axes connecting the ends of the electrode axes of nine electrodes and the vertical was 5 degrees or more.

Next, the relationship between the lighting direction of the comparative lamp, that is, the angle at which the electrode axial gravity line crosses the lead line, and the state of change in the arc shape will be explained with reference to FIG. Figure A shows the case of vertical lighting, where the high-temperature arc a comes into contact with a part of the coil of the cathode (4), so the temperature of the coil rises and the arc spot (10a)
As the pressure inside the arc tube (1) increases, the cathode (4) gradually increases.
) It is considered that devitrification and cracks do not occur in the arc tube (1) because the light is transferred to the tip. Figure B shows vertical lighting, but when the angle between the electrode axis and the vertical is 5 degrees or more, the arc 00 moves away from the cathode (4) due to gravity and approaches the arc tube wall, so the arc in the coil section Since the thermal influence from The wall of the arc tube close to α0) is exposed to extremely high temperatures for a long period of time, making it susceptible to devitrification and cracking.

Furthermore, when the horizontal lighting in Figure C, that is, the angle the electrode axis makes with the vertical reaches 90 degrees, the arc (IG) becomes susceptible to the influence of the cautious force, and the arc (a) is pushed up significantly and the arc tube Contacting or getting too close to the wall overheats the tube wall, and since the transfer of the arc spot (10a) to the cathode tip is less likely to occur than in the case of Figure B, the tube wall of the arc tube becomes more devitrified and cranks. considered to be a thing.

To summarize the above results, as the angle between the electrode axis and the vertical increases toward the horizontal lighting direction, the incidence of devitrification and cracking in the arc tube near the cathode sealing end gradually increases. In addition, if the cathode is coated with an insulating material over most of the surface of the root side of the electrode shaft, that is, the length l) from the sealed end to the bottom end of the coil, devitrification occurs regardless of whether the cathode is lit vertically or horizontally.

This means that no cracks will occur.

Next, the range covered by the insulator (5) was examined.

In the above example, most of the surface of the length from the sealed end of the cathode electrode shaft to the bottom end of the coil was covered with the insulator (5). The occurrence of arc spots, devitrification, and cracks in the arc tube was observed when the length 1) of the coated portion was varied. Note 9
The lighting direction is devitrified as shown above.

The test was carried out with horizontal lighting where cracks are most likely to occur.

As a result, the outer diameter d@ of the electrode coil (4b) of the cathode (4)
m), the length l (mm) from the sealed end of the cathode electrode shaft (4a) to the lower end of the coil, and the length t (111711) of the covered portion of the insulator (5) from the sealed end If the relationship is t≧ld, the arc spot always moves to the tip of the cathode, and no devitrification or cracking occurred in the arc tube 9.

In other words, if the insulator (5) is covered within the above range, an arc spot will be formed at the part (2-1) where the insulator (5) of the electrode shaft (4a) is not covered immediately after discharge. Even if the arc occurs, the temperature of the coil (4b) increases as the arc comes into contact with a part of the coil (4b), and the arc spot gradually moves toward the coil as the pressure inside the arc tube increases, eventually reaching the cathode. It moved to the tip of (4). As a result, the arc tube near the cathode (4) is not heated to a very high temperature by the arc spot for a long period of time, and devitrification and cracks are prevented from occurring.

On the other hand, the area where the insulator of the electrode shaft is not covered (
l-1) becomes larger, that is, the closer the arc spot is generated to the sealing end, the arc 1 becomes closer to the coil (4b
), the temperature rise in the coil (4b) section becomes slow, and the arc spot does not move to the cathode tip, resulting in devitrification of the arc tube.

This makes it easier for cracks to occur.

Further, the above results were similar even when the electrode shape was different, for example, when the tip of the electrode shaft did not protrude from the upper end of the coil.

It should be noted that the present invention is not limited to the small metal halide lamp of the above embodiment, and the same effects can be obtained with medium and large metal halide lamps. A similar effect can be obtained with other metal vapor discharge lamps that are lit in the same manner, such as high-pressure mercury lamps and high-pressure sodium lamps. That is, the arc tube of the high-pressure sodium lamp is formed by sealing the openings at both ends of a translucent ceramic tube with a closure body, such as a ceramic closure body, that supports an electrode. The lower end of the electrode shaft is joined to and supported by a lead-in wire made of niobium or the like that passes through the electrode shaft. Therefore, during discharge, an arc spot is formed on the electric gauge axis or lead-in wire near the joint, and if this state continues for a long time, devitrification may occur in ceramic tubes, but not in quartz glass tubes. In particular, problems such as the occurrence of cracks in the glass lead-in portion that airtightly holds the lead-in wire due to overheating occur, but by applying the present invention, such problems can be prevented. In the case of this lamp, the range l of the electrode axis is the sum of the length of the lead-in wire protruding from the glass-and-ruder sealed end and the length of the electrode axis up to the lower end of the coil.

〔Effect of the invention〕

As described in detail above, according to the present invention, a long-life metal vapor discharge lamp can be obtained in which no devitrification or cracks occur in the arc tube even when the lamp is lit with a power source such as DC lighting whose polarity is often reversed.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between changes in the metal halide shape according to an embodiment of the present invention) 11'n 1-tF>S. (1)... Arc tube, (2)... Arc tube bulb, (3
)···anode. (4)...Cathode, (4a)...Cathode electrode axis. (4b)...Cathode coil, (5)...Insulator. (6a), (6b)...Representative for the sealing department of arc tube bulbs: Kensuke Chika, patent attorney (and one other person)

Claims (1)

[Claims] The anode and cathode are sealed facing each other at both ends of the arc tube pulp.
In a metal vapor discharge lamp, which has an arc tube filled with a starting rare gas and a filler containing at least mercury, and is lit by a power source with no polarity reversal, the cathode is a part of the electrode shaft. It is made by winding a coil, and the outer diameter of the coil is d.
(gm), where the length of the electrode shaft from the cathode sealed end to the lower end of the coil is l (gm), the surface of the electrode shaft is insulated over a range of (ld) or more from the sealed end. A metal vapor discharge lamp characterized by being covered with a material.