JPH07296779A - High pressure sodium lamp - Google Patents

Abstract

PURPOSE:To suppress the blacking of an outer bulb inner surface by the evaporation of a current fuse constituting component. CONSTITUTION:A niobium conductor 3 has an electrode bar 4 having an electrode 2 on one end part, and a niobium tube 5 having an opening part on one end and a blocked part on the other end, and the other end of the electrode bar 4 is inserted through the blocked part of the niobium tube 5. A light emitting tube 1 is formed by sealing the niobium conductor 3 into both ends of a light permeable alumina tube by a flit 6, and sodium, mercury, and xenon are sealed in the inner part. Metal sleeves 9 are pressed and fixed to both ends of a current fuse 8, one end of the current fuse 8 is connected to the other end of the electrode bar 4, and the other end is connected to one stem support wire 10. The electrode bar 4 on the side having the current fuse 8 mounted thereon has a ceramic cylindrical insulating heat shielding body 11 having a collar part 11a so as to shield the heat radiation from the light emitting tube 1. The light emitting tube 1 is housed in an outer tube 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high pressure sodium lamp having a current fuse built in an outer tube.

[0002]

2. Description of the Related Art A high-pressure sodium lamp is a translucent alumina tube in which niobium conductors having electrodes are sealed at both ends.
In addition, it has a structure in which an arc tube in which mercury, sodium, and a rare gas for starting are enclosed is housed in an outer tube made of glass. In the high-pressure sodium lamp configured as above, when one electrode is broken due to excessive mechanical shock to the lamp, etc., when the power supply voltage is applied to the lamp, the tip of the broken electrode rod and other Discharge starts in the arc tube between the normal electrodes at the ends. In this case, since the electron emission performance at the tip of the broken electrode rod was significantly inferior to that of the normal electrode at the other end, the discharge current flowed a lot in the half cycle in which the normal electrode side became negative and remained broken. In the half cycle in which the tip side of the electrode rod becomes negative, the current almost stops flowing, and it becomes close to a half-wave rectified current. When such a state continues, the iron core of the ballast is magnetically saturated by the DC component of the current, so that an extremely large current flows through the ballast and the lamp as compared with the normal operation. As a result, the temperature of the ballast rises excessively and eventually the ballast burns out. As one of means for solving such a problem, a current fuse is interposed in a part of a current supply circuit to the arc tube in the outer tube of the lamp, and when the excessive current as described above flows, the current fuse is There is a structure that fuses to protect the ballast.

The simplest structure of a lamp using such a current fuse is to directly connect the current fuse between one of the niobium conductors at both ends of the arc tube and the stem support wire. . Since the current fuse is an extremely thin wire, it is difficult to maintain the reliability of the welded portion if it is directly welded to the stem support wire and the niobium conductor of the arc tube. A sleeve of a suitable length made of a material such as iron is covered, and this is crimped to the current fuse wire, and then this portion is welded to the stem support wire and the niobium conductor of the arc tube.

[0004]

However, the high-pressure sodium lamp incorporating such a current fuse has the following problems.
During lighting, the constituent components of the sleeve, such as nickel and iron, gradually evaporate from the welding point to the high-temperature niobium conductor, and this locally adheres to the inner surface of the glass outer tube near the welding point. It was found that the glass outer tube in the part gradually became black and caused a decrease in luminous flux. In the case of a standard lamp with an elliptical outer tube, the inner area of the outer tube is large and the distance between the inner surface of the outer tube and the current fuse weld is large, so the degree of blackening of the inner surface of the outer tube is extremely small, which is a particular problem. However, in a compact type lamp with an extremely small outer bulb, blackening of the outer bulb due to long-time lighting becomes remarkable.

As a means for suppressing the evaporation of such a metal sleeve, it is conceivable to adopt molybdenum or niobium, which has a low saturated vapor pressure at the operating temperature, as the sleeve material. It is very expensive and not a viable solution.

The present invention has been made in view of the above problems, and provides a high-pressure sodium lamp capable of suppressing blackening of the inner surface of an outer tube without using an expensive high heat-resistant metal sleeve. The purpose is to

[0007]

In the high pressure sodium lamp of the present invention, a niobium conductor having electrodes is sealed at both ends of a translucent alumina tube, and sodium, mercury and a rare gas are sealed inside. A high pressure sodium lamp in which an arc tube is housed in an outer tube made of glass, and a current fuse is provided by welding between one of the niobium conductors of the arc tube and one stem support wire supporting the arc tube. There, an insulating heat shield is arranged between the niobium conductor to which the current fuse is attached and a welding point where the current fuse is welded, and the coldest part is the arc tube during operation of the lamp. Of the both ends of the current fuse is located at the end on the side to which the current fuse is attached.

[0008]

With this structure, the operating temperature of the welding point of the current fuse to the niobium conductor is reduced, so that the evaporation of the components of the current fuse from the welding point is suppressed, and therefore the blackening of the inner surface of the glass outer tube is suppressed. To be done.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a high pressure sodium lamp which is an embodiment of the present invention. The niobium conductor 3 is
It is composed of an electrode rod 4 having an electrode 2 at one end and a niobium tube 5 having an opening at one end and a closing portion at the other end, with the other end of the electrode rod 4 being inserted through the closing portion of the niobium tube 5. Have The arc tube 1 includes a niobium conductor 3 and a frit 6
Is formed by sealing the both ends of the translucent alumina tube. The arc tube 1 is filled with sodium, mercury and xenon. During operation of the lamp, excess sodium and mercury are condensed in the amalgam 7 at the coldest part in the arc tube. A metal sleeve 9 made of nickel is crimped to both ends of the current fuse 8, one end of the current fuse 8 is connected to the other end of the electrode rod 4, and the other end of the current fuse 8 is one stem. It is connected to the support line 10. On the electrode rod 5 of the arc tube 1 on the side to which the current fuse 8 is attached, a ceramic cylindrical insulating heat shield 11 having, for example, a collar portion 11a for blocking heat radiation from the arc tube 1 is provided. It is inserted and provided. The heat shield 11 is held by the support plate 12 on the stem support wire 10 in an electrically insulating manner. The electrode rod 4 at the other end of the arc tube 1 is connected to the stem support wire 13. The arc tube 1 is housed in an outer tube 16, and the inside of the outer tube 16 is kept in a high vacuum. At both ends of the arc tube 1 are tantalum foils 1 and 1 for keeping the arc tube ends at an appropriate temperature during operation of the lamp.
5 is wrapped around. The length of the tantalum foils 14 and 15 in the axial direction of the arc tube is longer than that of the tantalum foil 15, and even if there is an unavoidable dimensional variation in the manufacture of the lamp, it must be ensured during the operation of the lamp. So that the coldest part of the arc tube 1 is located on the side where the current fuse 8 is attached,
Each length is set. Reference numeral 17 is a getter for maintaining a high vacuum inside the outer tube, 18 is a mouthpiece, and 19 is a stem.

With such a structure, the heat radiation of the arc tube 1 can be shielded by the heat shield 11, so that the temperature of the welded portion of the current fuse 8 can be suppressed to a minimum, and from the welding point during the operation of the lamp. It is possible to suppress the evaporation of components of the current fuse and to suppress the occurrence of blackening of the inner surface of the outer tube.

Further, by arranging the end portion of the arc tube on the side to which the current fuse 8 is attached so as to be located on the opposite side of the base 18 in the outer tube 16, the blackening of the inner surface of the outer tube is further generated. Can be suppressed.

[0013]

As described above, the present invention does not use an expensive material for the metal sleeves crimped at both ends of the current fuse in order to secure the reliability of the welding, and the metal caused by heat during lamp operation is used. It is possible to provide a high-pressure sodium lamp capable of significantly suppressing blackening of the inner surface of the outer tube due to evaporation of constituent components of the sleeve.

[Brief description of drawings]

FIG. 1 is an enlarged front view of a notched portion of a high-pressure sodium lamp according to an embodiment of the present invention.

FIG. 2 is a front view of a high-pressure sodium lamp that is an embodiment of the present invention.

[Explanation of symbols]

 1 arc tube 3 niobium conductor 8 current fuse 11 insulating heat shield

Claims (2)

[Claims] 1. A light-emitting tube in which a niobium conductor having electrodes is sealed at both ends of a translucent alumina tube and sodium, mercury and a rare gas are sealed inside is housed in an outer tube made of glass, A high-pressure sodium lamp in which a current fuse is provided by welding between one of the niobium conductors of the arc tube and one stem support wire that supports the arc tube, wherein the niobium conductive material with the current fuse attached An insulating heat shield is placed between the body and the welding point where the current fuse is welded, and the coldest part of the end of the arc tube where the current fuse is attached is located during operation of the lamp. High pressure sodium lamp characterized by being at the end. 2. The high-pressure sodium lamp according to claim 1, wherein the arc tube end on the side to which the current fuse is attached is arranged so as to be located on the side opposite to the base in the outer tube.