JP2002163911A - Electric discharge valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric discharge valve, which is made compact, has few heat degradation of an insulated sleeve, and moreover can secure insulation between an electric path of a minus side and the minus side in an insulated base, by preparing a suitable design criteria of the distance between the insulated sleeve and an arc tube. SOLUTION: The electric discharge valve is equipped with the insulating base 51, the arc tube 20 having an electric discharge light emitting part 22, which is arranged so that it may come out ahead of the insulating base 51 at both the forward and backward, and inserted into the both-ends pinch seal parts 23a and 23b, in which electrode assemblies are sealed, a lead support 52, which comes out from the insulating base 51 in parallel with the arc tube 20, and connects to a front end side lead wire c of the arc tube 20, and the insulated sleeve 53 equipped by the lead support 52. By separating between the electric discharge light emitting part center c of the arc tube 20 and the insulated sleeve 53 to estrange 5 mm or more, the degradation of the insulated sleeve 53 by generation of heat of the arc tube 20 is suppressed. Moreover, the insulation between the plus side terminal conducted to the electrode assembly of the back end side, and prepared in the back side of the insulating base 51, and the minus side terminal which conducts to the lead support, is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc tube having a discharge light emitting portion sandwiched between pinch seal portions at both ends sealing an electrode assembly, and a metal tube electrically connected to a lead wire on the front end side of the arc tube. And a discharge support having a structure in which the lead support is disposed in parallel.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional discharge bulb of this type comprises an insulating base 5, an arc tube 1 whose rear end is fixedly held by the base 5 and extends forward, and A metal lead support 3 extending forward in parallel with the arc tube 1 and supporting the front end of the arc tube 1. Reference numeral 4 denotes an adhesive for adhering and fixing the rear end side of the arc tube 1 to the base 5.

The arc tube 1 has a pinch seal 1
A closed glass bulb 2 serving as a discharge light emitting portion is sandwiched between a and 1b, and cylindrical portions 1c and 1c serving as non-pinch seal portions are formed before and after the pinch seal portions 1a and 1b. Reference numeral a denotes an electrode opposed to the sealed glass bulb 2 serving as a discharge light emitting unit, reference numeral b denotes molybdenum foil, and reference numeral c denotes a lead wire, which is integrated as an electrode assembly. Symbol 3a
Is a circular pipe-shaped insulating sleeve mounted on the lead support 3, which prevents discharge between the lead support 3 and the electrode assembly and protects the lead support 3 which is exposed to a high temperature during discharge emission of the arc tube 1. It is for.

Reference numeral 1d denotes a cylindrical shroud glass having an ultraviolet shielding effect, and is provided with a pinch seal portion 1a,
1b, it is welded and integrated to the arc tube 1 so as to cover the area of the closed glass bulb 2.

A lead wire c extending from the front end pinch seal portion 1a of the arc tube 1 is fixed to the front end of the lead support 3 by welding, and the rear end of the lead support 3 is attached to the outer periphery of the insulating base 5. It is welded and fixed to the peripheral negative terminal 7a.

On the other hand, a lead wire c extending from the pinch seal portion 1b on the rear end side of the arc tube 1 penetrates the back wall of the insulating base and is provided with a positive side cap provided to be exposed on the back side of the insulating base. It is fixed to the mold terminal 7b by welding.

Reference numeral 8 is a reflector for forming a low beam, and a discharge bulb is inserted into the bulb insertion hole 8b.
For example, when light emission from the closed glass sphere 2 is guided only to the effective reflection surface 8a, a light distribution made of metal that blocks light directed to a portion other than the effective reflection surface 8a of the reflector and forms a clear cut line of the light distribution pattern. A control shade 9 is provided.

[0008]

In recent years, a compact discharge bulb using a small arc tube has been developed. However, a high voltage of about 20 KV is applied to the discharge bulb at the start of lighting, and the arc during lighting is started. The discharge emission center of the tube has a high temperature of about 1000 ° C. For this reason, it is desired to ensure the heat resistance and the voltage resistance of the discharge bulb.

However, if the distance between the lead support 3 and the arc tube 1 is made too short in order to pursue a compact discharge bulb, there is a problem that the heat generated by the arc tube 1 deteriorates the insulating sleeve 3a. If the distance between the lead support 3 and the arc tube 1 is too short, the distance between the plus side and the minus side terminals 7b and 7a on the back side of the insulating base 5 also becomes short.
There is a possibility that a dielectric breakdown such as discharge between a and 7b may occur. On the other hand, if the distance between the lead support 3 and the arc tube 1 is too large in order to enhance the insulation (withstand voltage), the insulating base 5 becomes large, or the valve insertion hole 8b provided in the reflector 8 becomes large. As a result, problems such as a reduction in the area of the effective reflection surface 8a of the reflector 8 occur.

Therefore, when designing a discharge bulb,
Design multiple discharge bulbs with different distances between the lead support and the arc tube, repeat the heat resistance and insulation tests for each prototype, and mass-produce products with appropriate test data. Had become.

That is, conventionally, since there is no appropriate design standard for the distance between the lead support and the arc tube, for example, various types of discharge bulbs having different distances between the lead support and the arc tube are designed, prototyped, and tested. Must be performed, and before deciding on the product configuration,
There was a problem that it took a lot of time and effort.

If the inventor sets an appropriate design standard for the distance between the insulating sleeve and the center of the arc tube discharge / light emitting portion, the design options are narrowed down and the design is facilitated. We thought that the number of target prototypes could be reduced, reducing the time and effort spent deciding on a product configuration.

The present invention has been made on the basis of the above-mentioned problems of the prior art and the above-mentioned knowledge of the inventor. Accordingly, an object of the present invention is to provide an inexpensive discharge bulb which is compact and does not cause thermal deterioration of the insulating sleeve, and which can ensure insulation between the current supply paths on the plus side and the minus side in the insulation base.

[0014]

In order to achieve the above object, in a discharge bulb according to the present invention,
An insulating base, an arc tube having a discharge light emitting portion sandwiched between pinch seal portions at both ends which are arranged so as to extend forward and backward in front of the insulating base and seal the electrode assembly, and from the insulating base. In a discharge bulb comprising: a lead support extending in parallel with the arc tube and conducting to a front end side lead wire of the arc tube; and an insulating sleeve mounted on the lead support, a discharge light emitting portion of the arc tube. The center and the insulating sleeve were separated from each other by 5 mm or more.

(Function) When the distance between the center of the discharge light emitting portion, which is the highest temperature in the arc tube, and the insulating sleeve is 4 mm or less, the insulating sleeve may be deteriorated by the heat generated by the arc tube. By separating the insulating sleeve from the center by 5 mm or more, deterioration of the insulating sleeve due to heat generated by the arc tube is suppressed.

Generally, on the back side of the insulating base, a first terminal for conducting to the electrode assembly on the rear end side of the arc tube is provided substantially coaxially with the discharge axis of the arc tube, and at the front end side of the arc tube. A second terminal electrically connected to the electrode assembly (via a lead support) is provided substantially coaxially with the insulating sleeve. In the embodiment, the second terminal is provided on the outer periphery of the cylindrical portion on the back side of the insulating base surrounding the first terminal in the form of a belt separated by the distance between the insulating sleeve and the center of the arc tube discharge light emitting portion. When the distance between the center of the discharge light emitting portion and the insulating sleeve is short (4 mm or less), the distance between the first terminal and the second terminal also becomes short, and one becomes a plus side and the other becomes a minus side. Discharge occurs between the two terminals (between the first terminal and the second terminal), and insulation between the two terminals cannot be obtained, which may result in dielectric breakdown. However, the center of the discharge light emitting portion and the insulating sleeve are separated by 5 mm or more. Thus, the distance between the positive and negative current paths including the terminals is separated by 5 mm or more, and the discharge between the positive and negative current paths is suppressed.

Further, the discharge bulb is designed based on an appropriate design standard (5 mm or more) of the distance between the insulating sleeve and the center of the arc tube discharge light emitting section, and a prototype is manufactured and tested, thereby forming the discharge bulb as a product. The time and effort spent on determining is reduced.

According to a second aspect of the present invention, in the discharge bulb according to the first aspect, the discharge bulb is used as a light source of a vehicular lamp provided with a reflector for reflecting light emitted from a discharge light emitting portion of the arc tube forward. Wherein the distance between the center of the discharge light emitting portion of the arc tube and the insulating sleeve is 13 mm or less. (Function) When the distance between the insulating sleeve and the arc tube is too short (when the distance between the center of the discharge light emitting portion of the arc tube and the insulating sleeve is 4 mm or less), the shadow of the insulating sleeve is included in the light distribution formed by the reflected light of the reflector. However, since the insulating sleeve is separated from the center of the discharge light emitting portion of the arc tube by 5 mm or more, the shadow of the insulating sleeve that appears in the light distribution of the lamp is small and inconspicuous.

The discharge bulb is used as a lamp by being inserted into a bulb insertion hole which is an insulating base mounting portion provided at the rear top portion of the reflector. The reflector reflects the light emitted from the discharge light emitting portion of the arc tube and contributes to the formation of the light distribution.However, near the center of the reflector, the light distribution per unit area is larger than that at the periphery, and the light distribution is higher. This is the site that most affects light formation. If the distance between the insulating sleeve and the arc tube is large, the area of the effective reflecting surface of the reflector is reduced by an increase in the size of the insulating base or the size of the bulb insertion hole. It is not preferable because it decreases. Therefore, the distance between the center of the discharge light emitting portion of the arc tube and the insulating sleeve is reduced to 13 mm or less to reduce the size of the insulating base and the diameter of the bulb insertion hole.

According to a third aspect of the present invention, in the discharge bulb according to the first or second aspect, the discharge bulb is used as a light source of a vehicle lamp equipped with a metal light distribution control shade. The portion or the front end side lead wire exposed from the insulating base of the lead support,
Each was configured to be separated from the light distribution control shade by 5 mm or more.

(Function) If the distance between the portion of the lead support, which is an energizing path, exposed from the insulating base or the front end side lead wire and the light distribution control shade is too short, the light distribution control of the lead support or the front end side lead wire is performed. The part closest to the shade is discharged toward the light distribution control shade, and insulation may not be obtained. However, the parts closest to the shade of the lead support and the front end side lead wire are each 5 mm.
By separating as described above, the discharge between the lead support, the front end side lead wire, and the light distribution control shade can be suppressed.

[0022]

Next, embodiments of the present invention will be described based on examples.

FIGS. 1 to 3 show a first embodiment of the present invention. FIG. 1 is a longitudinal section showing a first embodiment of the present invention in which a discharge bulb is inserted into a low-beam forming reflector. FIGS. 2A and 2B show the thermal degradation of the insulating sleeve and the change in the distance between the center of the discharge light emitting portion of the arc tube and the insulating sleeve.
FIG. 3 is a diagram showing the withstand voltage (insulation) of the insulating base and the suitability of light distribution, and FIG. 3 is a diagram showing the suitability of insulation with respect to a change in the shortest distance between the lead support / lead wire and the light distribution control shade.

In FIG. 1, the arc tube 20 has a sealed glass bulb 22 which is a discharge light emitting portion formed in the middle of the glass tube in the longitudinal direction, and pinch seal sections 23a, 23b having a rectangular cross section before and after the sealed glass bulb 22. Are formed so that cylindrical portions 24a and 24b, which are non-pinch seal portions, extend in front of and behind the pinch seal portions 23a and 23b, respectively, and have a rod shape as a whole.

The electrodes a, a are opposed to each other in a hermetically sealed glass bulb 22 sealed by pinch seal portions 23a, 23b in which an electrode assembly in which the electrode a, the molybdenum foil b, and the lead wire c are integrated is sealed respectively. At the same time, a sealing material such as a starting rare gas, mercury, and a metal halide is sealed. Pinch seal portions 23 at both ends of closed glass bulb 22
a, 23b, lead wires c, c connected to the molybdenum foils b, b, respectively, are drawn out, and the cylindrical portions 24a, 24b
And extends forward and backward of the arc tube 20.

A cylindrical shroud glass 30 for shielding ultraviolet rays is welded and integrated to the arc tube 20.
Sealed glass bulb 22 and pinch seal portions 23a, 23b
Are covered with the shroud glass 30.
As a result, ultraviolet rays in a wavelength range harmful to the human body are cut off from the light emission of the closed glass bulb 22, and the glass is not scattered even if the closed glass bulb 22 ruptures.

The shroud glass 30 forms a closed space 34 isolated from the atmosphere around the arc tube 20 (closed glass bulb 22). The sealed space 34 is filled with argon gas from which the atmosphere is discharged and the water concentration is minimized, and the pressure in the sealed space 34 is about 1 atm when the high temperature arc tube is turned on. When it is not lit (normal temperature), the pressure is adjusted to about 0.5 atm. As a result, the airtightness of the sealed space 34 in which almost no moisture is present is ensured, so that devitrification does not occur in the arc tube.

As shown in FIG. 1, the discharge bulb is composed of a rod-shaped arc tube 20 and an insulating base 51 made of synthetic resin for supporting the arc tube 20. The front end of the arc tube 20 that is supported and extends forward is supported by a metal lead support 52 that extends from the insulating base 51 in parallel with the arc tube 20.

That is, the rear end side of the shroud glass 30 of the arc tube 20 is gripped by the metal gripping member 54 fixed to the front surface of the insulating base 51, and one lead support projecting forward of the insulating base 51. 5
The arc tube 20 is fixedly integrated with the insulating base 51 by supporting the front end portion of the arc tube 20 by 2. The lead support 52 is covered with a circular pipe-shaped insulating sleeve 53 that is made of ceramic and extends straight to suppress discharge between the lead support 52 and the rear-end electrode assembly.
The read support 52 is protected from the high temperature at the time of the discharge light emission of 0.

A front end side lead wire c extending from the arc tube 20 is fixed to the front end of the lead support 52 by welding, and the rear end of the lead support 52 is connected to the insulating base 51.
Negative belt-shaped terminal 5 provided around the back side outer periphery
5 is fixed by welding.

On the other hand, the rear end side lead wire c penetrates the bottom wall 51b of the base 51 on which the concave portion 51a is formed, and is fixed by welding to the plus side cap type terminal 56 provided to be exposed on the back side of the insulating base. ing. The terminal 56 is provided coaxially with the arc tube 20, and the center of the terminal 56 and the belt-shaped terminal 55 are separated by the distance between the center C of the discharge light emitting portion of the arc tube 20 and the insulating sleeve 53.
Further, a cylindrical portion extending rearward is provided between the terminals 55 and 56 in a wall shape, and the extending surface distance between the terminals 55 and 56 is increased, so that a compact and large withstand voltage is secured. ing.

Reference numeral 57 denotes an output cord extending from, for example, a ballast circuit unit (not shown) fixed to the lower part of the lamp body. The output cord is connected to the rear end (terminals 55 and 56) of the insulating base 51 via the connector 58. It is connected.

Reference numeral 60 denotes a reflector made of a synthetic resin for forming a low beam, and an aluminum vapor-deposited film constituting a reflection surface is formed on the surface thereof. Then, the light emitted from the arc tube 20 (the closed glass bulb 22) is reflected forward by the upper effective reflection surface 61 of the reflector 60, whereby a predetermined light distribution is formed.

At the position below the discharge bulb in the reflector 60, its leg 72 is fixed near the bulb insertion hole 64, and covers the lower, front and obliquely upper front of the lead support 52 for light distribution control made of metal. Is provided, and the shroud glass 40 is also provided with a light-shielding coating portion 40 for controlling light distribution.

That is, the upper rear edge 71 of the light distribution control shade 70 is located on a line connecting the discharge light emitting portion center C and the upper parting line 61a of the effective reflection surface 61 of the reflector 60. Then, the light emitted from the closed glass bulb 22 and directed downward, forward, and obliquely forward and upward (forward from the upper parting line 61a of the effective reflection surface 61) is shielded. further,
The light distribution control shade 70 is formed with a light-shielding portion (not shown) for forming a clear cut line, and provides clear clear light distribution of a low-pass beam formed by light reflected on the effective reflection surface 61. It contributes to the formation of cut lines.

The light-shielding coating portion 40 for light distribution control formed on the outer peripheral surface of the shroud glass 30 has a pair of right and left clear cut lines extending in a front and rear band shape on the left and right side surfaces of the shroud glass 30. The lower parting line 6 of the paint part 42 and the effective reflection surface 61 of the reflector 60 extending in a strip shape across the upper surface of the shroud glass 30 from side to side.
1b.

The upper rear edge 71 of the shade 70
And the arc-shaped light-shielding coating portion 44 cooperate to form the closed glass bulb 22.
The upper edge 43 of the linear light-shielding coating portion 42 and a light-shielding portion (not shown) for forming a clear cut line of the shade 70 for light distribution control are shielded. To form a clear cut line in the light distribution of the passing beam.

In order to form a clear clear cut line in the light distribution of the passing beam, a light shielding portion (not shown) for forming a clear cut line of the light distribution controlling shade 70 is required. The linear light-shielding coating portions 42 for forming the clear cut lines provided on the left and right side surfaces of the glass 30 are not always necessary.

FIG. 2 shows that the distance d1 between the discharge light emitting portion center C of the arc tube and the insulating sleeve 53 is 4 mm to 1 mm.
Thermal degradation of insulation sleeve and withstand voltage of insulation base (insulation property) for structures that differ in increments of 1 mm up to 4 mm
And the experimental data verifying the suitability of the light distribution. Based on the experimental data, the distance d1 between the discharge light emitting center C of the arc tube 20 and the insulating sleeve 53 is set to 5 mm or more and 13 mm or less.

That is, if the distance d1 is 4 mm or less, as shown in FIG. 2A, the heat generated by the arc tube 20 (the closed glass bulb 22) may deteriorate the insulating sleeve 53. In order to avoid thermal deterioration, it is desirable that the distance d1 be 5 mm or more.

When the distance d1 is 4 mm or less, the distance between the cap-type terminal 56 and the belt-shaped terminal 55 provided on the back side of the insulating base 51 is also about 4 mm or less, and FIG. As shown in (1), there is a high possibility that discharge occurs between the terminals 55 and 56. Therefore, in order to prevent a discharge between the terminals 55 and 56 and to secure a withstand voltage in the insulating base 51, it is desirable that the distance d1 be 5 mm or more.

Further, as shown in FIG. 2C, when the distance d1 is 4 mm or less, the shadow of the insulating sleeve 53 appears largely in the light distribution of the low beam formed by the reflector 60, which is notably unfavorable. . Therefore,
In order to make the shadow of the insulating sleeve 53 appearing in the light distribution of the passing beam small and inconspicuous, it is desirable that the distance d1 be 5 mm or more.

The discharge bulb is inserted into a bulb insertion hole 64 provided at the rear top of the reflector 60 and used as a lamp. The central portion of the reflector 60 is a place where the amount of luminous flux per unit area is larger than that of the periphery, and is a portion which has the greatest influence on the light distribution formation. When the distance between the insulating sleeve 53 and the center of the arc tube discharge light emitting portion is large, the insulating base 51 becomes large,
As the valve insertion hole 64 becomes larger, the area of the effective reflection surface of the reflector 60 is reduced, so that the light amount is reduced and the solid angle is reduced, which is not preferable. Therefore, in the present embodiment, the distance between the center C of the discharge light emitting portion of the arc tube and the insulating sleeve 53 is configured to be 13 mm or less, so that the insulating base 51 is made compact and the diameter of the valve insertion hole 64 is reduced. As a result, a light distribution with a sufficient amount of light is formed.

The shortest distance d2 between the portion of the lead support 52 exposed from the insulating sleeve 53 and the light distribution control shade 70, and the shortest distance d3 between the front end side lead wire and the light distribution control shade 70, respectively. It is set to 5 mm or more.

That is, the lead support 52 extending forward of the insulating base 51 is formed in a shape bent upward, and this bent portion of the lead support is the portion closest to the shade 70. Further, the tip of the front end side lead wire c which is welded and fixed to the tip of the lead support 52 is the portion closest to the shade 70. Then, the shortest distance d2 between the exposed portion of the lead support 52 and the shade 70
And the shortest distance d between the front end side lead wire c and the shade 70
3 is 4 mm or less, the lead support 52 and the front end side lead wire c discharge to the shade 70, respectively, and the shortest distances d2 and d3 may be 4.5 mm and the shortest distances d2 and d3 may be 5 mm or more. It has been verified by the inventor's experiment shown in FIG. 3 that no discharge occurs. Therefore, in the present embodiment, these shortest distances d2,
The distance d3 is set to 5 mm or more to ensure insulation between the lead support 52 and the light distribution control shade 70 and between the front end lead c and the light distribution control shade 70.

The lead support 52 and the reflector 6
If the distance between the 0 reflective surfaces (aluminum deposited film) is too small,
Although there is a concern about discharge at a portion of the lead support 52 that is close to the reflector reflection surface, a portion of the lead support 52 that is close to the reflector reflection surface is an insulating sleeve 53.
And there is no possibility that dielectric breakdown will occur between the lead support 52 and the reflector reflecting surface.

[0047]

As is apparent from the above description, according to the first aspect, the deterioration of the insulating sleeve due to the influence of heat generation of the arc tube is suppressed, and the heat resistance of the insulating sleeve is ensured, and the insulating property is improved. Discharge between the positive and negative current paths in the base is suppressed, and the insulation durability of the insulating base is also ensured.

Further, since the time and labor required to determine the configuration of the discharge bulb as a product is reduced, the insulation sleeve is not thermally degraded, and the discharge bulb in which the insulation property is ensured in the insulation base is low. Can be offered at a price.

According to the second aspect, since the insulating base does not increase in size, a compact discharge bulb can be obtained. Further, since the light distribution of the lamp is not affected by the shadow of the insulating sleeve, and the bulb insertion hole does not become large, the intended light distribution having a sufficient light amount can be obtained.

According to the third aspect, the discharge between the lead support or the front end side lead wire and the light distribution control shade, which is a current supply path to the front end side electrode assembly of the arc tube, is suppressed. Provided is a discharge bulb in which insulation between a side lead wire and a shade is ensured.

[0051]

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a state in which a discharge bulb according to a first embodiment of the present invention is inserted into a traveling beam forming reflector.

FIG. 2 is a view showing thermal degradation of an insulating sleeve, withstand voltage (insulating property) of an insulating base, and suitability of light distribution with respect to a change in a distance between the center of a discharge light emitting portion of an arc tube and a lead support.

FIG. 3 is a diagram showing the suitability of insulation for a change in the shortest distance between a lead support / lead wire and a light distribution control shade.

FIG. 4 is a longitudinal sectional view of a reflector having a conventional discharge bulb inserted therein.

[Explanation of symbols]

Reference Signs a Electrode b Molybdenum foil c Lead wire 20 Arc tube 22 Sealed glass sphere as discharge light emitting part 23a, 23b Pinch seal part 30 Shroud glass 40 (42, 44) Light distribution control light shielding film 42 Straight line for forming clear cut line Light-shielding film 51 Insulating base made of synthetic resin 52 Metal lead support 53 Insulating sleeve made of ceramic 56 Cap-shaped terminal which is the first terminal on the plus side 57 Second belt-shaped terminal on the minus side 60 Reflector 61 Effective reflection Surface 70 Shade for light distribution control C Center of discharge light emitting section d1 Distance between arc tube discharge light emitting section center and insulating sleeve d2 Shortest distance between lead support and light distribution control shade d3 Front end side lead wire and light distribution control shade Shortest distance between

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yukihiro Kobayakawa 500 Kitawaki, Shimizu-shi, Shizuoka Prefecture F-term in the Koito Manufacturing Shizuoka Plant (reference) EC01

Claims (3)

[Claims] 1. An arc tube having an insulating base, a discharge light emitting portion disposed between front and rear portions of the insulating base, the discharge light emitting portion sandwiched between pinch seal portions at both ends sealing an electrode assembly, A discharge support comprising: a lead support extending from the insulating base in parallel with the arc tube and conducting to a front end side lead wire of the arc tube; and an insulating sleeve mounted on the lead support. A discharge bulb wherein a center of a discharge light emitting portion of a tube and the insulating sleeve are separated by 5 mm or more. 2. The discharge bulb is used as a light source of a vehicular lamp provided with a reflector for reflecting light emitted from a discharge light emitting portion of the arc tube forward. The discharge bulb according to claim 1, wherein the distance between the lead supports is configured to be 13 mm or less. 3. The discharge bulb is used as a light source of a vehicular lamp provided with a metal light distribution control shade, and includes a portion exposed from an insulating base of the lead support or a front end side lead wire. The discharge bulb according to claim 1, wherein each of the discharge bulbs is separated from the light distribution control shade by 5 mm or more.