JPH0612607Y2 - Metal halide lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an improvement in a metal halide lamp in which a metal halide is enclosed in an arc tube made of a translucent alumina ceramic tube, and in particular, an end structure of the arc tube is improved. Regarding

[Prior Art] Compared with a metal halide lamp for general lighting, in order to raise its operating temperature and obtain higher efficiency and better color rendering, it is replaced with a quartz arc tube and has higher heat resistance than quartz.
In addition, various attempts have been made to use a translucent alumina ceramic tube having excellent chemical stability.

As an arc tube of a metal halide lamp using this type of ceramic arc tube, for example, Japanese Patent Application Laid-Open No. 52-71695.
An arc tube having the structure shown in FIG. 2 disclosed in Japanese Patent Publication has been proposed.

In the figure, reference numeral 21 denotes a ceramic arc tube, and a conductive cermet end cap 22 made of alumina and tungsten metal is hermetically sealed at both ends of a straight pipe by a sealing agent 23. , An electrode mandrel 25 having a tungsten coil 24 at the tip inside the tube of the end cap
A lead rod 26 is embedded on the outside.

A rare gas is enclosed in the tube together with mercury and a metal halide.

[Problems to be Solved by the Invention] However, when the lamp having the arc tube is turned on, the surplus additive in the enclosed additive (metal halide) is the root part of the electrode mandrel which is the coldest part in the arc tube. Light emitted from the arc that adheres to the vicinity of the arc is absorbed near the root of the arc, and the uniformity of the light emitted from the arc tube is poor. There was a problem.

Further, as disclosed in Japanese Patent Laid-Open No. 61-245459, there is provided an arc tube having a different diameter in which both ends of a straight tube type alumina tube are integrally formed with thin ends via shoulders. Proposed. This has an advantage over the straight tube type alumina arc tube as shown in FIG. 2 in that the arc between both electrodes is stable.

However, there is a drawback that the surplus additive adheres to the boundary between the straight tube portion and the shoulder portion and the vicinity of the root portion of the electrode core rod, and arcs are generated from both to leak the arc tube.

The present invention has been made in view of the above, and in a metal halide lamp in which a translucent alumina tube is used as an arc tube and an end cap made of a conductive cermet is sealed at its end, a cermet end cap of the arc tube is provided. It is an object of the present invention to provide a lamp having an improved structure of the sealing portion, having a long life, high efficiency and high color rendering properties, good uniformity, and no uneven light emission.

In the lamp according to the present invention, in order to prevent uneven light emission due to the excess additive existing in the vicinity of the electrode during lighting, the excess additive is condensed at the base of the electrode so as not to interfere with the radiated light emitted from the arc. As described above, it is possible to form a concave portion at the base of the electrode with respect to the discharge space so that the emitted light can be substantially effective and uniform, and can be put to practical use as a light source for optical equipment.

It should be noted that the arc tube including the spherical light emitting portion according to the present invention is well known as a quartz tube, but is not used for a polycrystalline alumina tube having a low linear transmittance. This is generally used for small quartz arc tubes in order to increase unevenness in light emission and luminous efficiency, but alumina tubes have good diffusivity and thermal conductivity, and the arc tube shape may be a straight tube. Is.

[Means for Solving the Problems] An example in which the present invention is applied to a short arc type metal halide lamp for optical equipment will be described below with reference to FIG.

A translucent alumina tube 11 in which a spherical light-emitting portion is integrally formed with a cylindrical neck portion having a diameter smaller than that of the light-emitting portion at both ends thereof
An end cap 12 made of a conductive cermet made of convex alumina-tungsten is hermetically sealed to the end portion of the via a sealing agent 13. Further, an electrode mandrel 15 made of tungsten having a tungsten coil 14 wound around the tip thereof is embedded in the center portion of the end cap on the tube inner end surface side, and a lead rod 16 made of tungsten, molybdenum or the like is embedded and fixed on the tube outer end surface side. There is.

The other end of the arc tube has a structure in which an alumina tube and a cermet are integrally sintered without using a sealing agent.

Here, the cermet end cap is made by sintering a mixture of aluminum oxide and tungsten metal, and has a volume resistivity value of 10 mn · cm to 10 ⁻³ mn · cm, which is more conductive. Prevents excessive heating due to operating current during operation.

An alumina layer 17 having a thickness of 1 mm or less is integrally sintered with a cermet end cap, which is a base, on the surface of the end cap exposed to the inner surface of the arc tube, thereby providing a structure for electrical insulation. . This can prevent the occurrence of discharge from the surface of the end cap and the instability of the arc, resulting in light flicker and color unevenness.

Further, 17 indicates a surplus additive of metal halide.

[Example] As the arc tube configured as described above, an inner diameter of 10
mm, end (neck diameter) 4 mm, arc length 5 mm, lamp length 35 mm in an arc tube of indium iodide, thallium iodide, lithium iodide and a predetermined amount of mercury, and argon gas as a starting rare gas at 100 Torr 150 W This metal halide lamp was prototyped, placed at a predetermined position on the parabolic mirror of the optical device, then turned on, and the illuminance unevenness and color unevenness of the light emitted from the front surface of the mirror were measured. The improvement of the characteristics was recognized.

In addition, in the above-mentioned examples, iodides of indium, thallium, and lithium were used as the additives, but almost the same effect could be obtained by using other additives.

[Effects of the Invention] As is apparent from the above description, the metal halide lamp according to the present invention causes unevenness in color by aggregating the excess additive at the time of lighting the arc tube in the recess formed in the electrode neck of the arc tube end. It is possible to obtain a ceramic metal halide lamp with no unevenness in illuminance.

[Brief description of drawings]

FIG. 1 is a partially longitudinal side view showing an embodiment of an arc tube of a metal halide lamp according to the present invention, and FIG. 2 is a side view showing a conventional lamp.

Claims (2)

[Scope of utility model registration request] 1. A metal halide having an arc tube in which an end cap made of a conductive cermet in which electrodes and lead rods are embedded and fixed is hermetically sealed at the end of a translucent alumina ceramic tube having a spherical light emitting part in the center. In the lamp, a cylindrical neck portion having a diameter smaller than that of the spherical light emitting portion is formed at an end portion of the ceramic tube, and a surface position of the end cap inside the light emitting tube is lower than a boundary between the light emitting portion and the neck portion. A metal halide lamp that is located at the bottom to form a concave space. 2. The metal halide lamp according to claim 1, wherein an insulating layer is formed on the inner surface of the arc tube of the end cap.