JPH0447948B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a small metal vapor discharge lamp that is operated using a power source such as direct current that does not have polarity reversal. [Technical background of the invention and its problems] In recent years, from the perspective of energy saving, there has been active development of metal vapor discharge lamps with excellent luminous efficiency, such as metal halide lamps, which can be used in place of incandescent bulbs with low luminous efficiency. is being advanced. These metal vapor discharge lamps are usually lit via a ballast using a general power supply of AC 100V or 200V with a commercial frequency of 50Hz or 60Hz, and the ballast is installed in a separate location from the discharge lamp. A method is being taken. However, when considering it as an alternative to incandescent light bulbs, which are often used indoors in households and stores, it is essential that the lamp and ballast be integrated, and that the ballast be compact, lightweight, and inexpensive. be. However, it is considered difficult to satisfy the above conditions with the currently common ballast using a chiyoke coil. In recent years, with the development of transistors, ICs, etc., it has become possible to construct an electronic circuit as a ballast that can satisfy the above conditions. Possible methods for such electronic circuits include DC lighting methods and high-frequency lighting methods, but with high-frequency lighting methods, a phenomenon called acoustic resonance occurs in a specific frequency band, causing the arc to fluctuate.
This may cause the product to disappear. In particular, in the case of metal halide lamps, the frequency band in which acoustic resonance occurs is extremely wide due to the influence of the arc tube shape, the enclosed material, etc., making them unsuitable for high-frequency lighting systems. Therefore,
In particular, for electronic ballasts for metal halide lamps, it is desirable to use a lighting system that uses a power source that does not have polarity reversal, such as direct current. In the process of developing metal vapor discharge lamps such as metal halide lamps that use a DC power source with no polarity reversal, the present inventors developed an electrode with a coil wound around the tip of an electrode shaft designed for conventional AC lighting. If a discharge lamp with the above-mentioned polarity is not reversed, it will cause devitrification and cracks on the tube wall near the cathode.
It was discovered that many lamps were malfunctioning due to arc tube leaks. Furthermore, it has been found that this phenomenon becomes more severe in smaller lamps of 100 W or less, where the cathode and the wall of the arc tube are closer together. We further observed these phenomena by comparing them with AC-lit lamps, and found that even if the lamp is stable in a steady state, if it is lit with a power source that does not have polarity reversal, an arc spot will be formed on the sealed side of the cathode. It was found that there were cases in which the spot did not migrate to the cathode tip, and it was found that most of the lamps that were left on for a long time in this state caused the above-mentioned cracks. 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 in all lamps moved to the tip of the electrode 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 time passes, the temperature inside the arc tube increases,
The pressure inside the arc tube increases to a high pressure of 1 atm or more during rated lighting, for example in metal halide lamps.
It can reach around 10 atmospheres or more. 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). Then, the discharge distance d moves in the direction of becoming 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 on the entire electrode and the tip of the electrode is also heated. As the arc increases, it easily moves to the tip of the electrode, but in cases where there is no reversal of polarity, such as with direct current, the arc becomes a spot on the cathode side, concentrating only on a small part of the electrode sealing side, and only in that concentrated area. is heated. Moreover, since the coil part acts like a heat dissipation fin, the temperature at the tip of the electrode does not rise to a level sufficient to emit electrons even if the pressure inside the arc tube increases sufficiently, and furthermore, since there is no reversal of polarity, the temperature at the tip of the electrode does not rise sufficiently to emit electrons. It is inferred that the movement of the arc from the spot position may not occur unless some kind of force is applied. Therefore, if an arc spot occurs on the sealed end side of the cathode and does not migrate to the cathode tip,
The high-temperature arc approaches and contacts the arc tube wall for a long time, resulting in devitrification and cracks on the tube wall. Moreover, the fact that an arc can occur at the sealed end side or the tip of the cathode means that the arc length is different, and if the arc length is different, the lamp voltage will also be different, so the lamp voltage will remain constant each time it is lit. This results in the inconvenience of not doing so. [Object of the invention] The present invention has been made in consideration of the above circumstances, and
A small metal vapor of 100W or less that does not cause devitrification or cracks in the arc tube when lit with a power source that does not have polarity reversal, such as DC, and has stable characteristics with a long life and little fluctuation in lamp voltage. The purpose is to provide discharge lamps. [Summary of the Invention] The present invention provides a cathode in which a high-melting point metal rod is inserted into both ends of a coil, that is, the tip side, and an electrode shaft is inserted into the sealed end, and the high-melting point metal rod and the electrode are inserted into the cathode. A gap is formed inside the coil by arranging the fitting ends of the shafts apart from each other, and the length of the gap is l (mm), and the total length of the coil is L.
(mm), the outer diameter of the coil is D (mm), the inner diameter of the coil is d
(mm), the diameter of the electrode shaft on the sealed end side is d ₁ (mm), and the steady state discharge current is I _L (unbeared), 1.5≦D/d=4 ...(1) 14≦I _L /d ² ₁ ≦350...(2) l≧L/3...(3). [Embodiments of the Invention] Details of the present invention will be described below with reference to illustrated embodiments. Figure 1 shows the arc tube 1 of a 40W class small metal halide lamp, with a maximum inner diameter of approximately 8.
Inside the light-emitting bulb 2 made of quartz glass formed into an approximately spherical shape of mm, 100 Torr of argon gas, 10 mg of mercury, and a total of 2 mg of metal halides such as scandium iodide and sodium iodide are sealed. Further, an anode 3 and a cathode 4 are sealed facing each other at both ends of the arc tube bulb 2 with an interval of 4 mm between them. Cathode 4 has a wire diameter of 0.1mm
The total length L of the tungsten wire wound is 2 mm.
A high melting point metal rod 6 made of tungsten, for example, is inserted into the tip side of the coil 5 having an outer diameter D of 0.35 mm and an inner diameter d of 0.15 mm, and an electrode shaft 7 also made of tungsten is inserted into the sealed end side. It consists of The ends of the rod-shaped body 6 and the electrode 7 inserted into the coil 5 are spaced apart from each other, thereby forming a gap 8 with a length l of 1 mm inside the coil. The body 6 is configured to protrude by approximately 0.4 mm. In other words, the coil outer diameter DN
The ratio D/d to the coil inner diameter d is given by the above equation (1), 1.5≦
D/d=0.35mm/0.15mm=2, which satisfies D/d≦4, and the relationship between the length l of the void 8 formed in the coil 5 and the total length L of the coil 5 is as shown above (3 ) formula l≦L/
3 is satisfied. l=L/2. On the other hand, the anode 3 is constructed by winding a tungsten wire with a wire diameter of 0.06 mm around a tungsten wire with a wire diameter of 0.19 mm into a coil, which is further wound into a double coil 10 around a tungsten electrode shaft 9 with a diameter of 0.22 mm. The total length of the double coil 10 is 1.5 mm. Anode 3
and the cathode 4 are sealed at both ends of the arc tube bulb 2,
Molybdenum foil 12 hermetically sealed inside 11b
External lead wires 13a, 13b via a, 12b
are connected to each other to form an arc tube 1. Although not shown, the arc tube 1 is normally sealed within an outer tube with a cap attached to one end, and the external lead wires 13a and 13b are connected to the cap and the terminal, respectively, to form a lamp. A lamp having such a configuration is connected to an AC power source 15 via a DC lighting electronic circuit ballast 14, as shown in FIG. 2, for example. The ballast 14 is AC/
It includes a DC converter 16 and a current detection circuit 17. A starting circuit 18 applies a starting pulse voltage between the cathode 4 and the anode 3. The ballast 14 and starting circuit 18 apply a discharge current I _L of 0.56 A (ampere) to the arc tube 1 during steady operation, and control the lamp input to 40 W (watts) during stable lighting. . Therefore, light axis d ₁ is 0.15mm
The current density at the cross section of the electrode shaft 7 is: discharge current I _L /(light diameter d ₁ ) ² = 0.56 A/(0.15 mm) ² ≒25, and this value is expressed by equation (2) above, 14≦I _L / d ₁ ² ≦350 is satisfied. Each of the above 10 lamps is lit by the above lighting device.
When a flashing test was conducted 100 times, no phenomenon was observed that occurred at the base of the cathode 4 (the sealed end side of the electrode shaft 7) of the arc during stable lighting. The reason for this is that the void 8 is provided in the cathode coil 5, so even if an arc occurs at the root of the cathode 4 during startup, the entire inside of the coil 5 is filled with the electrode shaft and the void is filled. Since the mass of that part is smaller than that of a part without it, that is, its heat capacity is small, the temperature easily rises, and the cathode tip quickly rises to a temperature at which an arc is likely to occur. Then, as the stable lighting state progresses, the metal inside the arc tube 1 evaporates and the vapor pressure rises, and the arc attempts to shorten the distance as much as possible, eventually transitioning to an arc between the tips of the electrodes 3 and 4. reach. Therefore, during stable lighting, there is no arc generation point at the base of the cathode 4, so the quartz glass of the arc tube 1 will not be abnormally heated and cause devitrification or cracks, resulting in a long life and stable lighting. Since the arc length does not change over time, there is no inconvenience that the lamp voltage changes. Moreover,
Since the cathode 5 is provided with a coil 5, the glow voltage is low, and by providing a void 8 in the coil, the mass can be reduced compared to an electrode with the same appearance but the entire inside of the coil is filled with electrode shafts. , the transition from glow discharge to arc discharge is good and the starting characteristics are also excellent. Furthermore, since the arc is generated from the protruding tip of the rod 6 at the tip of the cathode during steady lighting, there is also the advantage that the arc spot is stable. Next, the results of tests conducted to determine the preferred range of cathode structure will be described. The test lamp was a 40W metal halide lamp having the same structure as the above example, and only the structure of the cathode 4 was changed to examine the effect on the lamp characteristics. The table shows the test contents and results, and the factors that cause variations in the cathode structure include the shaft diameter d ₁ of the electrode shaft 7.
(mm), the outer diameter of the coil D (mm), the inner diameter d (mm), the overall length L (mm), the length l (mm) of the internal cavity 8, and the coil type (single layer and multilayer). The evaluation was determined by comparing and examining the starting characteristics and life characteristics, taking into account the difficulty of transitioning from glow discharge to arc discharge, the difficulty of transitioning the arc spot from the cathode root to the cathode tip, etc. In addition, in the cathode shape used in this test, as can be seen from Fig. 1, the shaft diameter d ₁ of the electrode shaft 7 and the coil inner diameter d
are substantially the same. Further, the entire length of the rod-shaped body 6 inserted into the tip end side of the coil 5 and the length of the rod-shaped body 6 protruding from the coil 5 are all the same dimensions as in the above embodiment.

【table】

〔Effect of the invention〕

As detailed above, according to the present invention, when lighting is performed using a power source that does not have polarity reversal, such as DC lighting, even if an arc occurs at the base of the cathode during startup, it quickly moves to the tip of the arc tube. Loss of clarity and cracks due to abnormal heating of the tube wall can be prevented, resulting in a long service life.Also, during steady lighting, the arc is generated from the high melting point metal rod at the tip of the cathode, so the arc spot is stable and the arc is removed every time the tube is lit. Since the length does not change, the lamp voltage remains constant. Moreover, since the cathode is equipped with a coil, the glow voltage is low.
Furthermore, since there is a void inside the coil, the mass can be reduced, so that effects such as good transition from glow discharge to arc discharge and excellent starting characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a front view of an arc tube of a small metal halide lamp according to an embodiment of the present invention, and FIG. 2 is a diagram showing a lighting device for the same lamp. DESCRIPTION OF SYMBOLS 1... Arc tube, 2... Arc tube bulb, 3... Anode, 4... Cathode, 5... Cathode coil, 6... High melting point metal rod, 7... Cathode electrode shaft, 14...
Ballast, 16... AC/DC converter, 17...
Current detection circuit, 18...starting circuit.

Claims (1)

[Scope of Claims] 1. An arc tube comprising an anode and a cathode sealed opposite to each other at both ends of the bulb, and a starting rare gas and a filler containing at least mercury sealed inside. In a small metal vapor discharge lamp of 100W or less that is lit by a power source with no polarity reversal, the cathode has a high melting point metal rod on the tip side of the coil and an electrode shaft on the sealed end side. The ends of the high melting point metal rod and the electrode shaft are spaced apart from each other to form a gap inside the coil, and the length of this gap is l (mm), and the length of the gap is l (mm), The total length of is L (mm), the outer diameter of the coil is D (mm), the inner diameter of the coil is d (mm), the diameter of the electrode shaft on the sealed end side is d ₁ (mm), and the discharge current at steady state is I _L
(Ampere), 1.5≦D/d=4 14≦I _L /d ² ₁ ≦350 l≧L/3.