JP2008210551A - Metal halide lamp, metal halide lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To substantially improve durability of a dc lighting type mercury free metal halide lamp. <P>SOLUTION: A discharge vessel 1 is formed by sealing parts 12a, 12b provided at both ends of a discharge space 14 filled with a discharge medium containing a halide and noble gas and containing no mercury in essence. An anode 3a2 and a cathode 3b2 are disposed face to face in the discharge space 14. One end part of metal foil 3a1 and one end of metal foil 3b1 are combined with the base side end part of the anode 3b2 and the base side end part of the cathode 3b2 respectively. The metal foil 3a1, 3b1 is airtightly sealed by the sealing parts 12a, 12b. The other ends of the metal foil 3a2, 3b2 are combined with external leads 3a3, 3b3 respectively, and are led out to the outside of the sealing parts 12a, 12b. The direction of a current flowing in the discharge vessel 11 is fixed, and the metal foil 3a1 on the anode 3a2 side and the external lead 3a3 connected to this metal foil 3a1 are coated with a rhenium metal film 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a discharge lamp, and more particularly to a mercury-free metal halide lamp and a metal halide lamp lighting device using direct current lighting.

Conventional mercury-free metal halide lamps that do not use mercury have a problem in that the metal foil made of molybdenum foil or the like that ensures the airtightness of the discharge vessel is likely to react with the discharge medium. In order to prevent the reaction with the discharge medium and to improve the life characteristics due to the absence of mercury. (For example, Patent Document 1)
JP 2002-260581 A

  The technique of the above-mentioned Patent Document 1 has an advantage when a mercury-free metal halide lamp is turned on by direct current, in the case of an automotive headlamp, an AC conversion circuit necessary for alternating current lighting is unnecessary, Due to the electric field in the direction, metallic elements such as Sc and Na are attracted to the cathode, and the arc tube becomes clouded and Na is lost on the cathode side. These phenomena are less on the anode side, and generally direct current emits light. It is conceivable that the cloudiness of the tube and the lack of Na are less, and the flicker is less.

However, the encapsulated metal halide decomposes into metal and halogen in the arc during lighting. Each is partially ionized, the metal becomes a cation, the halogen becomes an anion, and in the case of zinc iodide (ZnI ₂ ), Zn ⁺ and I ⁻ are present in the arc.

In a mercury-free halogen lamp, since a high vapor pressure, for example, a kind of zinc iodide as a second halide is enclosed as a lamp voltage forming substance, the amount of halogen anion (I ⁻ ) in the lamp is large. The halogen anion (I ⁻ ) is attracted to the anode in direct current lighting, and then passes between the electrode shaft and the quartz glass in a state presumed to be neutral halogen (I) and reaches the metal foil. To produce molybdenum iodide (MoI ₂ ). Since molybdenum iodide (MoI ₂ ) has a much lower density than Mo, the volume increases when Mo changes to molybdenum iodide (MoI ₂ ) and exerts a great deal of stress on the surrounding quartz glass.

In a lamp that frequently passes a large current during start-up, such as an automobile headlamp, when the above reaction occurs, a crack occurs in the quartz glass of the sealing part in a very short time, and the arc tube leaks and is inconvenient. Become. In addition, the metal foil on the anode side of DC lighting is much more likely to be molybdenum iodide (MoI ₂ ) than the metal foil on both sides of AC lighting and the metal foil on the cathode side of DC lighting. Spots are very likely to occur. For this reason, the life characteristics have been deteriorated.

  An object of the present invention is to provide a mercury-free metal halide lamp and a metal halide lamp lighting device that have improved life characteristics in a direct current lighting system.

  In order to solve the above-described problems, a metal halide lamp according to the present invention includes a discharge vessel having a discharge space and sealing portions provided at both ends of the discharge space, and an anode disposed to face the discharge space. And a cathode, a metal foil having one end bonded to the base side end of the anode and the cathode, and hermetically sealed by the sealing portion, respectively bonded to the other end of the metal foil, and A pair of external leads led out of the sealing portion; and a discharge medium enclosed in the discharge vessel, containing a halide and a rare gas, and essentially free of mercury. The direction of the current flowing in the container is constant, and at least the metal foil on the anode side and the external lead connected to the metal foil are covered with a rhenium metal film.

  According to the present invention, the life characteristics can be greatly improved by using a mercury-free lamp with a direct current lighting system and coating the anode side metal foil, the external lead and the rhenium metal film on the anode.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIGS. 1 and 2 are schematic configuration diagrams, and FIG. 2 is an enlarged configuration diagram of FIG. 1, for explaining an embodiment of a metal halide lamp according to the present invention.

  Reference numeral 1 denotes an inner tube constituting a metal halide lamp. Plate-shaped sealing portions 12a and 12b are formed at both ends of the discharge vessel 11 at the center, and cylindrical unsealed at both ends. Stop portions 13a and 13b are formed. The inner tube 1 can be used as long as it is a material excellent in heat resistance and translucency. For example, quartz glass can be used.

  Inside the discharge vessel 11, a discharge space 14 having a substantially cylindrical shape at the center and a tapered shape at both ends in the axial direction is formed. The volume of the discharge space 14 is preferably 100 μl or less for a short arc type discharge lamp, and the volume of the discharge space is preferably 10 μl to 40 μl when an application is specified for an automotive headlamp.

  The discharge space 14 is filled with a discharge medium composed of the metal halide 2 and a rare gas, and the discharge medium essentially does not contain mercury. Next, a specific example of the discharge medium will be described.

  First, as the metal halide, halides of various metal elements can be used. For example, a first metal halide that mainly contributes to light emission is used. As the first halide, a halide of one or more kinds of metal elements selected from sodium (Na), scandium (Sc), and a rare earth metal is used. Na and Sc are particularly efficient luminous materials.

  The metal halide has a vapor pressure that is relatively high and includes one or more types of metal halides that do not easily emit light in the visible light region as compared to the metal of the first halide as the second halide. Can do. The metal that does not easily emit light in the visible light region has a higher energy level than the metal of the first halide and may be in a state where the metal of the first halide mainly emits light. By adding the second halide, a lamp voltage close to that of a lamp containing mercury can be obtained, and the electrical characteristics and light emission characteristics of the mercury-free metal halide lamp can be improved. The second halide contributes to chromaticity improvement and the like.

  Examples of the second halide include magnesium (Mg), iron (Fe), cobalt (Co), chromium (Cr), zinc (Zn), nickel (Ni), manganese (Mn), aluminum (Al), and antimony. One or more selected from (Sb), beryllium (Be), rhenium (Re), gallium (Ga), indium (In), titanium (Ti), zirconium (Zr), hafnium (Hf) and tin (Sn) These metal halides are used.

  As the halogen constituting the metal halide, iodine (I) is most suitable in terms of low reactivity, and the reactivity increases in the order of bromine (Br), chlorine (Cl), and fluorine (F), but is necessary. It is possible to select appropriately according to. Further, different halogen compounds such as iodide and bromide can be used in combination.

  As for the amount of metal halide to be enclosed, for example, the first halide that mainly contributes to light emission can be enclosed in the range of 5 mg to 110 mg per 1 cc of the internal volume of the discharge vessel (volume of the discharge space). A more preferable range is 5 mg to 35 mg per 1 cc of the internal volume of the discharge vessel. In such a range, the rise of the luminous flux can be accelerated and the light color can be stabilized. The second halide can be enclosed in the range of 0.05 mg to 200 mg per 1 cc of the internal volume of the discharge vessel. About other halides, it adjusts suitably.

  In addition to the starting gas and the buffer gas, the rare gas acts to emit main light immediately after the starting. Generally, it is not particularly limited as long as it does not pass through the discharge vessel, but when the discharge vessel is formed of quartz glass, argon (Ar), krypton (Kr), or xenon (Xe) is recommended. When light emission immediately after start-up depends on a rare gas, xenon is optimal because xenon has the highest luminous efficiency.

  When the enclosure pressure of the rare gas is increased, the lamp voltage is increased, and the lamp input can be increased for the same lamp current to improve the rising characteristics of the luminous flux. Good rise characteristics of the luminous flux are convenient for any purpose of use, but are particularly important for automotive headlamp devices and liquid crystal projectors. For example, the rare gas is sealed at a pressure of 3 atm or more, and is preferably sealed in a range of 5 to 15 atm.

  Further, “essentially no mercury is enclosed” is not limited to the state where mercury is not enclosed at all, and it is acceptable that less than 2 mg of mercury, preferably 1 mg or less of mercury exists per 1 cc of internal volume of the discharge vessel. Means. However, it is environmentally desirable that mercury is not encapsulated. In the case where the electrical characteristics of the discharge lamp are maintained by the conventional mercury vapor, the short arc type is filled with 20 mg to 40 mg of mercury per 1 cc of the internal volume of the discharge vessel, and in some cases, 50 mg or more of mercury. The amount of mercury used in is essentially low.

  In FIG. 1 again, mounts 3a and 3b are sealed inside the sealing portions 12a and 12b. The mounts 3a and 3b include metal foils 3a1 and 3b1, an anode 3a2, a cathode 3b2, and external leads 3a3 and 3b3. The metal foils 3a1 and 3b1 are strip-shaped thin metal plates having a high melting point such as, for example, molybdenum (Mo).

  Reference numeral 4 denotes rhenium (Re) metal coated on the metal foil 3a1 on the anode 3a2 side and the external lead 3a3 connected to the metal foil 3a1. The rhenium metal film 4 is coated with a film thickness in the range of 200 nm to 2500 nm by an ion plating method described later.

  FIG. 3 is a schematic configuration diagram for explaining a case where the metal halide lamp according to the present invention is applied to an automotive headlamp. The same components as those in FIG. The description will focus on the different parts.

  In FIG. 3, the arc tube constituting the main part of the metal halide lamp has a double tube structure, and an inner tube 1 made of, for example, quartz glass is disposed inside the arc tube. The inner tube 1 has an elongated shape in the lamp axis direction, and a substantially elliptical discharge vessel 11 is formed at a substantially central portion thereof. Plate-shaped sealing portions 12a and 12b are formed at both ends of the discharge vessel 11, and cylindrical non-sealing portions 13a and 13b are formed at both ends thereof.

  A socket 7 is connected to the non-sealing portion 13a side of the arc tube. The metal band 71 attached to the outer peripheral surface of the outer tube 9 near the non-sealing portion 13a is connected to the four metal tongue pieces 72 formed on the opening end of the socket 7 on the inner tube 1 holding side. (In FIG. 3, two are shown). And in order to strengthen a connection further, the contact point of the metal band 71 and the tongue piece 72 is welded. A terminal to which an external lead 3a3 and a support wire (not shown) are connected is formed at the bottom of the socket 7.

  The other ends of the external leads 3a3 and 3b3 whose one ends are connected to the end portions of the metal foils 3a1 and 3b1 extend to the outside of the sealing portions 12a and 12b along the tube axis. One end of an L-shaped support wire 6 made of nickel is connected to the external lead 3 b 3 extending to the outside, and the other end extends in the direction of the socket 7. A portion of the support wire 6 parallel to the tube axis is covered with an insulating sleeve 8 made of ceramic.

  Outside the inner tube 1 configured as described above, a cylindrical outer tube 9 in which a metal oxide having an ultraviolet blocking effect is added to quartz glass along the tube axis is provided substantially concentrically with the inner tube 1. It has been. The inner tube 1 and the outer tube 9 are connected by welding the outer tube 9 in the vicinity of the cylindrical non-sealing portions 13a and 13b at both ends of the inner tube 1, and the inner space is airtight. In the space, for example, a rare gas such as nitrogen, neon, argon, xenon, or the like can be sealed or mixed.

  FIG. 4 is an explanatory diagram for explaining a method of coating the rhenium metal film on the base side of the anode 3a2, the metal foil 3a1, and the external lead 3a3 connected to the metal foil 3a1 by ion plating. . FIG. 5 is an explanatory diagram for explaining a mount to which a rhenium metal film is applied.

  In FIG. 4, reference numeral 41 denotes a vacuum chamber that has been evacuated. A large number of mounts 3 a shown in FIG. 5A are attached to a substrate 43 installed on a substrate support 42 that serves as a cathode above the vacuum chamber 41. . At this time, the external lead 3a3 is fixed to the substrate 43 with the anode 3a2 facing downward. The rhenium metal Re placed on the evaporation table 44 below the vacuum chamber 41 is heated and evaporated by electrode discharge. By the high frequency coil 45 installed between the evaporation table 44 and the substrate 43, the evaporated rhenium metal Re is ionized and accelerated to cover the surface of the mount 3 a as the rhenium metal film 4.

  The entire vacuum chamber 41 is uniformly coated on the entire surface of the mount 3a by, for example, applying two types of rotation in the X-axis and Y-axis directions. At this time, the film thickness of the coating can be determined by controlling the output and time of the high frequency coil 45.

  Note that the anode 3a2 is bulky when the rhenium metal film is formed. Therefore, as shown in FIG. 5B, when the mount 3a ′ without the anode 3a2 is formed, the number of rhenium metal films that can be formed at a time can be increased. There is. The anode 3a2 and the metal foil 3a1 are joined using a joining means such as laser welding or resistance welding.

  The mount 3a thus coated with the rhenium metal film 4 is used in the metal halide lamp shown in FIG. The rhenium metal film 4 covered with the metal foil 3a1 prevents reaction of halogen (I) or the like to the metal foil 3a1. Further, the high-quality rhenium metal film 4 formed on the surface of the metal foil 3a1 can further strengthen the adhesion between the metal foil 3a1 and the quartz glass of the sealing portion 12a, and the sealing of the sealing portion 12a. It was found that the flashing characteristics could be improved by improving the power.

  The rhenium metal film 4 can be formed by a plating method in addition to the ion plating method. In the case of the plating method, the rhenium metal film 4 of the mount 3a is plated by supporting the external lead 3a3 side and plating the rhenium metal Re by immersing the mount 3a in FIG. Can be coated.

  Here, a specific example of application as a vehicle headlamp using the metal halide lamp of the present invention will be described with reference to FIG.

  The discharge vessel 1 made of quartz glass has an inner diameter A of 2.6 mm and is formed into a spheroidal shape. Elongated sealing portions 12a and 12b are provided at both ends of the major axis of the ellipse. The tip portions of the anode 3 a 2 and the cathode 3 b 2 are projected into the discharge space 14. The base portions of the anode 3a2 and the cathode 3b2 are welded to one ends of the metal foils 3a1 and 3b1, respectively, in the sealing portions 12a and 12b. The tip of the anode 3a2 has a sphere with a diameter B of 0.65 mm, an axial shape with a diameter C of 0.35 mm, and the material is doped tungsten. The cathode 3b2 has an axial shape with a diameter D of 0.35 mm, and the material is tungsten containing 1.0% tria. The distance E between the anode 3a2 and the cathode 3b2 is set to 4.2 mm.

  Further, the diameter F of the sealing portion 12a is 5 mm, and the metal foil 3a1 has a length of 12 mm, a thickness of 20 μm, and a width of 2.0 mm. In the discharge vessel 1, a rare gas, a first halide and a second halide are sealed as a discharge medium. The length of the metal foil 3b1 of the cathode 3b2 is 7 mm.

As the rare gas, 11 atm of xenon was enclosed. Further, 0.10 mg of scandium iodide (ScI ₃ ) and 0.25 mg of sodium iodide (NaI) were sealed as the first halide, and 0.12 mg of zinc iodide (ZnI ₂ ) was sealed as the second halide. .

(Example 1)
In Comparative Example 1, the thickness of the metal foil 3a1 of the anode 3a2 was 20 μm, the width was 2.0 mm, and the length was 7 mm. In Comparative Example 2, the thickness of the metal foil 3a1 of the anode 3a2 was 20 μm, the width was 2.0 mm, and the length was 14 mm.

  In the example, like the comparative example 1, the thickness of the metal foil 3a1 on the anode 3a2 side is 20 μm, the width is 2.0 mm, and the length is 7 mm. The metal foil 3a1 and the external lead 3a3 are joined by welding. The mount 3a ′ in the state 5 (b) was formed by forming a rhenium metal film 4 with a film thickness of 400 nm by an ion plating method.

  Three types of metal halide lamps with the specifications of metal foil 3a1 and external lead 3a3 are manufactured, and the following lighting tests A to D are performed using a DC lighting circuit. The DC power is 75W at start-up and 35W DC at steady-state. I went there.

(1) Lighting test A
The three types of lamps of Comparative Examples 1 and 2 and Example were subjected to a continuous lighting test with 35 W input for 10 lamps.

  Regarding the joint between the metal foil 3a1 of the anode 3a2 and the external lead 3a3, the comparative example 1 was oxidized, and all the quartz in the vicinity cracked within 700 hours. In Comparative Example 2, since the metal foil 3a1 is long, the temperature of the joint portion between the metal foil 3a1 and the external lead 3a3 is lower than that of the comparative example 1, and the total number is cracked from the joint portion between the metal foil 3a1 and the external lead 3a3 until 700 hours. There was no.

  On the other hand, in the example, the temperature of the joint between the metal foil 3a1 and the external lead 3a3 was the same as that in Comparative Example 1, but the heat-resistant rhenium metal film 4 is coated, so that it is made of molybdenum. The external lead 3a3 and the metal foil 3a1 were not oxidized, and even after lighting for 5000 hours, the joint did not crack.

  If the metal foil 3a1 is lengthened as in the comparative example 2, cracks can be avoided, but the length of the sealing portion 12a increases and the compactness is lost, which is particularly a problem with automotive headlamps. Further, when the metal foil becomes longer, foil cracks are likely to occur.

  As for the reaction of the metal foil 3a1, in both Comparative Examples 1 and 2, the metal foil 3a1 is blackened from the anode 3a2 side by lighting for about 200 hours, and cracks enter the quartz glass in the vicinity thereof. In this case, the metal foil 3b1 on the cathode 3b2 side has a slow reaction and much less black discoloration, which is evidence of the formation of molybdenum iodide.

  In Comparative Example 2, cracks are not generated at the joint between the metal foil 3a1 and the external lead 3a3, but the reaction of the metal foil 3a1 and the accompanying crack in the quartz glass forming the sealing portion 12a from the vicinity of the metal foil 3a1. All the points became unsatisfactory within 1000 hours due to leakage.

  On the other hand, in the example, these two types of quartz cracks were hardly present, and lighting was possible for a total of 5000 hours.

(2) Lighting test B
A lighting test was performed in a cycle of lighting 10 seconds for each of the three types of lamps of Comparative Examples 1 and 2 and Example, with a cycle of lighting 0.5 seconds and lighting 4 seconds. This test eliminates the influence of the reaction between the metal foil 3a1 and free iodine (I) as much as possible, and evaluates the influence of the stress at the start-up related to the adhesion between the quartz glass of the sealing part 12a and the metal foil 3a1. It is to do.

  In Comparative Example 1, leakage and astigmatism occurred when the average blinked 8000 times, and in Comparative Example 2 leakage and astigmatism occurred when the average blinked 5000 times. It has been confirmed that the longer the metal foil 3a1, the more easily the foil cracks are generated.

  On the other hand, the example was able to blink more than 30,000 times. Comparing Comparative Example 1 and Examples, it was found that the adhesion between the quartz glass of the sealing portion 12a and the metal foil 3a1 was improved in the Examples. This is considered to be an effect that the rhenium metal film 4 is interposed between the sealing portion 12a made of quartz glass and the metal foil 3a1.

(3) Lighting test C
A lighting test was performed in a cycle of lighting for 3 seconds and turning off for 4 seconds for each of the three types of lamps of Comparative Examples 1 and 2 and Example. In this test, the influence of the reaction between the metal foil 3a1 and free iodine (I) increases.

  In Comparative Example 1, the average was 3000 times, and in Comparative Example 2, the average was 2500 times. In both cases, the metal foil 3a1 turns black due to the reaction, cracks are generated in the quartz glass near the metal foil 3a1, and leakage occurs from this, which becomes inconvenient. On the other hand, in the Example, blinking was possible 20,000 times or more.

(4) Lighting test D
A lighting test was performed in accordance with the flashing method of the Japan Light Bulb Industry Association Standard “JEL215”, 10 of the three types of lamps of Comparative Examples 1 and 2 and Example. This blinking is a combination of various lighting times and extinguishing times in one cycle and two hours, and evaluates overall life characteristics.

  Both Comparative Example 1 and Comparative Example 2 were all unsatisfactory within 300 hours of lighting. On the other hand, in Example, it was possible to turn on a total of 2000 hours or more.

(Example 2)
The lamp specification of Example 2 is the same as that of Example 1, and is the state shown in FIG. 5B in which a metal foil 3a1 having a thickness of 20 μm, a width of 2.0 mm, and a length of 7 mm is joined to an external lead 3a3 The mount 3a ′ is coated by changing the film thickness of the rhenium metal film 4 by an ion plating method. The film thickness was changed from 100 nm to 4000 nm (4 μm) by 100 nm.

  A lighting test was performed on each of the two metal halide lamps using a standard flashing method. As a result, the lighting time of 2000 hours or longer was in the range of film thickness 200-2500 nm. Furthermore, the suitable range in which the lighting time of 2500 hours or more was obtained was the range of 400-2000 nm. When the thickness of the rhenium metal film 4 is small, the reaction with the free halogen becomes remarkable as the lighting time elapses. On the other hand, when the film thickness is large, the adhesion of the sealing portion 12a to the quartz glass is lowered, and cracks are likely to occur in the quartz glass due to flashing stress.

(Example 3)
The lamp specification of this Example 3 is the same as that of Example 1, and the anode 3a3, the metal foil 3a1 having a thickness of 20 μm, the width of 2.0 mm, and the length of 7 mm, and the external lead 3a3 are joined together. Example 3A is a lamp in which the mount 3a in the state of) is covered with a 400 nm rhenium metal film 4 by ion plating.

  Similarly, the mount 3a ′ in the state of FIG. 5B in which the metal foil 3a1 having a thickness of 20 μm, a width of 2.0 mm, and a length of 7 mm and the external lead 3a3 are bonded to each other with a 400 nm thickness is formed by an ion plating method. A lamp in which the rhenium metal film 4 is coated and then the anode 3a3 is joined is referred to as Example 3-B.

  200 pieces of each of the two types of lamps of Examples 3-A and 3-B were lit up to 300 hours by the lighting system of the Japan Light Bulb Industry Association.

  During this lighting time, no flicker occurred in Example 3-A, but 12 flickers in Example 3-B. In Example 3-B, the electrode deformation of the anode is large and therefore flickering easily occurs. However, in Example 3-B, since the rhenium metal film 4 is coated on the anode 3a2, the deformation of the anode 3a2 is small, and flickering occurs. It never happened.

  FIG. 6 is a circuit diagram for explaining an embodiment relating to the lighting device of the present invention. In this embodiment, the metal halide lamp of the present invention is configured to be lit by direct current.

  In the figure, 61 is a DC power source, 62 is a chopper, 63 is a control unit, R is a lamp current detection means, VR is a lamp voltage detection means, 64 is a starting part, and 65 is a metal halide lamp having the configuration shown in FIG.

  As the DC power source 61, a battery or a rectified DC power source is used. In the case of an automobile, a battery is generally used. However, it may be a rectified DC power source that rectifies AC. If necessary, the electrolytic capacitor C is connected in parallel to perform smoothing.

  The chopper 62 converts the DC voltage into a voltage having a required value and controls the metal halide lamp 65 as required. When the DC power supply voltage is low, a step-up chopper is used, and when it is high, a step-down chopper is used.

  The control unit 63 controls the chopper 22. For example, immediately after the lamp is turned on, a lamp current more than three times the rated lamp current is supplied from the chopper 62 to the metal halide lamp 65, and thereafter, the lamp current is gradually reduced with the passage of time, and is controlled so as to eventually reach the rated lamp current. . In addition, the control unit 63 performs constant power control of the chopper 62 by generating a constant power control signal when a detection signal of the lamp current and the lamp voltage is fed back. Further, the control unit 63 includes a microcomputer in which a temporal control pattern is previously incorporated, and is configured to control the lamp current.

  The lamp current detection means R is inserted in series with the lamp, detects the lamp current, and inputs the control input to the control unit 63. The lamp voltage detection means VR is connected in parallel with the lamp, detects the lamp voltage, and inputs the control voltage to the control unit 23. The starting unit 64 is configured to supply a pulse voltage of 20 kV to the metal halide lamp 65 at the time of starting.

  Then, when the metal halide lamp is DC-lit using the metal halide lamp lighting device of this embodiment, a required light flux is generated immediately after lighting. As a result, it is possible to realize lighting with a luminous flux of 25% and a luminous flux of 80% after 4 seconds 1 second after turning on the power necessary as a vehicle headlamp. Further, the DC-AC conversion circuit is unnecessary, and it is possible to improve the life characteristics while enjoying the advantages of the metal halide lamp that is lit by DC.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram for demonstrating one Embodiment regarding the metal halide lamp of this invention. The block diagram which shows the enlarged view of the principal part of FIG. The schematic block diagram for demonstrating the case where the metal halide lamp of this invention is applied for vehicle headlamps. The conceptual diagram for demonstrating the film-forming of rhenium metal by an ion plating method. Explanatory drawing for demonstrating the target object which applies the rhenium metal film of this invention. The circuit diagram for demonstrating one Embodiment regarding the metal halide lamp lighting device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner tube 11 Discharge container 12a, 12b Sealing part 13a, 13b Non-sealing part 14 Discharge space 2 Metal halide 3a, 3b Mount 3a1, 3b1 Metal foil 3a2 Anode 3b2 Cathode 3a3, 3b3 External lead 4 Rhenium metal film 61 DC power supply 62 Chopper 63 Control unit 64 Start unit 65 Metal halide lamp R Lamp current detection means VR Lamp voltage detection means

Claims (4)

A discharge vessel having a discharge space and sealing portions provided at both ends of the discharge space;
An anode and a cathode disposed opposite to each other in the discharge space;
A metal foil having one end bonded to the base side end of the anode and the cathode and hermetically sealed by the sealing portion;
A pair of external leads respectively joined to the other end of the metal foil and led out of the sealing portion;
A discharge medium enclosed in the discharge vessel, containing a halide and a noble gas, and essentially free of mercury,
A metal halide lamp characterized in that the direction of current flowing in the discharge vessel is constant, and at least the metal foil on the anode side and the external lead connected to the metal foil are covered with a rhenium (Re) metal film.   2. The rhenium metal film is formed by coating the anode, the metal foil having one end coupled to the anode, and the external lead having one end coupled to the metal foil. Metal halide lamp.   3. The metal halide lamp according to claim 1, wherein the rhenium metal film has a thickness in a range of 200 nm to 2500 nm. The metal halide lamp according to any one of claims 1 to 3,
A metal halide lamp lighting device comprising: a lighting circuit that supplies a current that is always in a single direction to a metal halide lamp so that the current flows in the discharge vessel without changing with time.

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