JPS60220544A - Metal halide lamp for dc lighting - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a rise in starting voltage and a drop in light flux, by installing a light emitting tube whose both ends have the anode and the cathode, while letting the cathode take a core to be installed the light emitting tube in a non-seal state with a sealing part, a coil part whose one end is rolled on this core and a conductor part connected to metal foil at the other end. CONSTITUTION:A light emitting tube consists of quartz glass or the like, and the cathode 6 and the anode 7 at both sides of the tube are connected to each of external conductors 12 and 13 via metal foil sheets 10 and 11. The cathodes 6 is provided with a core 14 composed of a tungsten wire, a coil part 15 whose one end is rolled on this core and a conductor 17 with a coil composed of the tungsten wire having a conductor part 16. Inside the light emitting tube 5, a metal halide composed of, for example, scandium iodide and sodium iodide, mercury and argon gas of tens torr are sealed up. With this constitution, a loss of heat conduction ranging from a cathode tip part to a light emitting tube sealing part is restrained, and since a wire diameter of the core becoming a cathode luminescent spot is able to take it yet larger, temperature in the cathode tip part is reducible and, what is more, a rise in starting voltage and any drop in a light flux holding rate are all preventable from occurring.

Description

[Detailed description of the invention] Industrial applications The present invention relates to metal halide lamps.

Conventional structure and its problems Metal halide lamps are attracting attention as lamps with high efficiency and high color rendering properties. However, most low-wattage lamps for indoor lighting are mercury lamps.

Fluorescent lamps and incandescent bulbs are used. In recent years, from the standpoint of energy conservation, there has been a desire to develop compact metalloid lamps with high efficiency, high color rendering properties, and long life.

By the way, generally when a discharge lamp is operated with alternating current, a peak called a restriking voltage occurs in the lamp voltage when transitioning from one half cycle to the next half cycle.

A small metal halide lamp of 100 W or less has the drawback that a sharp restriking voltage peak occurs within several tens of seconds immediately after lighting, and when this peak exceeds the power supply voltage, the lamp goes out.

On the other hand, if a small metal lamp is lit with direct current, such a peak in the restriking voltage will not occur, and the lamp will not go out immediately after being lit once. From this point of view, direct current lighting is preferable for small metal-no-ride lamps.

FIGS. 1(a) and 1(b) show electrodes used in a conventional metal halide lamp for AC lighting. In the case of the figure (a), the structure consists of a core wire 1 and a coil 2 wound around one end of the core wire, and in the case of the figure (b), it is an integral structure with a coil 3 at one end and a conductor at the other end. It is of structure. Then, the other end of the core wire 1 or the other end of the conducting wire 4 on the side opposite to the side where the coils 2 and 3 are provided is sealed in a sealing part of an arc tube (not shown).

However, in a metal halide lamp for direct current lighting that uses a full electrode cathode with the structure shown in Figure (a), during glow discharge, there is a large heat conduction loss from the cathode tip to the arc tube sealing part, so arc discharge cannot occur. It is difficult to migrate, resulting in high starting voltage and blackening of the arc tube due to sputtering of the cathode. In addition, in a metal halide lamp for DC lighting that uses an electrode with the structure shown in Figure (b) as the cathode, the heat conduction loss from the cathode tip to the arc tube sealing part is small, so the increase in starting voltage can be suppressed. However, the temperature of the sealing part of the arc tube on the cathode side becomes low and the coldest part is formed.

Luminous flux decreases. Furthermore, the temperature at the tip of the cathode increases, and the arc tube becomes black due to evaporation of the cathode metal.

OBJECTS OF THE INVENTION The present invention provides a metal halide lamp for direct current lighting that prevents an increase in starting voltage and a decrease in luminous flux.

Structure of the Invention The metal halide lamp for direct current lighting of the present invention includes an arc tube having an anode and a cathode at both ends and a metal halide sealed inside, and the cathode is connected to this sealing part within the arc tube. and a core wire provided in an unsealed state, a coil portion with one end wound around the core wire, and a coil portion extending from the coil portion with the other end sealed in the sealing portion and connected to the metal foil. The invention is characterized in that it has a conductive wire portion.

This suppresses heat conduction loss from the cathode tip to the arc tube sealing portion and sputtering of the cathode.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a metal halide lamp for direct current lighting, which is an embodiment of the present invention.

In FIG. 2, the arc tube 6 is made of quartz glass or the like, and has a maximum inner diameter of 6 mm. A cathode 6 and an anode are provided at both ends of the arc tube 5. Cathode 6° Anode 7 is sealed part 8
, 9, a metal foil 10 made of molybdenum foil or the like,
11 to external conductors 12 and 13, respectively. As shown in Fig. 3, the cathode 6 has a wire diameter of 0-3 mm.
A tungsten wire with a wire diameter of Oj 5 mm, which has a core wire 14 consisting of a tungsten section, a coil portion 15 with one end wound around the core wire, and a conductive wire portion 16 extending from the coil portion and connected to the metal foil 10. A conductor 17 with a coil is provided. The anode 7 is made of a tungsten wire with a diameter o and a diameter of 26H.

The arc tube 5 is filled with metal halides of scandium iodide (ScI3) and sodium iodide (NaI) of tt 3 my, 4 mg of mercury, and argon gas of several tens of torr.

Such a metal halide lamp for DC lighting with lamp power of 40W, total lamp voltage of 70V, lamp current of 0.57A.
When we conducted a lighting test, the results were as shown in the table below. The same table also shows similar test results for metal halide lamps for direct current lighting (referred to as Comparative Example 1 and Comparative Example 2, respectively) using electrodes with the structures shown in Figures 1 (a) and (b) as cathodes. are also shown. Here, the core wire 1 of Comparative Example 1 is made of tungsten wire, and the wire diameter is 0.31.
11 m, and the coil 2 of Comparative Example 1 and Comparative Example 2
, 3 is made of tungsten wire and has a wire diameter of 0.25 mm.

*As can be seen from the table above after 6,000 hours of lighting, Comparative Example 1 has a high starting voltage because it is difficult to transition from glow discharge to arc discharge, and blackening of the arc tube occurs due to sputtering of the cathode, resulting in poor luminous flux maintenance. Further, in Comparative Example 2, the heat conduction loss from the cathode tip to the arc tube sealing portion is small, so the starting voltage is reduced. However, this lowers the temperature of the sealing part of the arc tube on the cathode side, creating the coldest part, resulting in a decrease in efficiency.

In contrast, the lamp of the present invention was good in all aspects of starting voltage, efficiency, and luminous flux maintenance rate. The reason why such good results were obtained is that heat conduction loss from the cathode tip to the arc tube sealing part is suppressed, and the wire diameter of the core wire that forms the cathode bright spot can be increased. This is because the temperature can be lowered.

Note that the lamp of the above embodiment had a structure in which the core wire 14 protruded from the end of the arc tube sealing part side of the coil part 16;
Similar results were obtained with a non-protruding structure.

Details of the invention As explained above, the present invention improves the starting voltage.

It is possible to provide an excellent metal halide lamp for DC lighting in which a decrease in luminous flux maintenance factor is suppressed.

[Brief explanation of drawings]

Figures 1 (a) and (b) are partially cutaway cross-sectional views showing conventional electrodes, Figure 2 is a front view of a metal halide lamp for direct current lighting, which is an embodiment of the present invention, and Figure 3 is a cathode. FIG. 2 is an enlarged sectional view of a main part. 5... Arc tube, 6... Cathode, 7...
・Anode, 8°9... Sealing part, 10, 11...
...Metal foil, 14... Core wire +15...
・Coil part, 16... Conductor part, 17...
・Conductor with coil.

Claims (1)

[Claims] A light emitting tube having an anode and a cathode at both ends and having a metal chloride sealed inside, the cathode being a core wire provided in the arc tube in an unsealed state with the sealing part, and It is notable that the wire has a coil part whose one end is wound around the core wire, and a conductor part which extends from the coil part and whose other end is sealed in the sealing part and connected to the metal foil. Metal halide lamp for direct current lighting.