JPH0258734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-pressure discharge lamp having an arc tube made of translucent single-crystal alumina, and particularly to the arc tube.

Incandescent light bulbs have become widely popular as one of the main lamps for indoor lighting because they have good color rendering properties and can be easily installed and removed even in ordinary homes. However, in the era of energy conservation, the low efficiency of incandescent light bulbs is becoming a problem, and recently there has been a strong demand for the development of compact, high-intensity discharge lamps to replace light bulbs.
Specifically, for example, a high-pressure sodium lamp using an arc tube made of single-crystal alumina, particularly a high-pressure sodium lamp with high color rendering properties. The arc tube of this high-pressure sodium lamp adopts the configuration shown in FIG. 1, which was previously proposed by the inventors. That is,
A configuration is adopted in which electrode conductors 2 and 3 are directly sealed to the inner surfaces of both ends of an arc tube 1 made of single-crystal alumina.

By the way, the first reason for adopting such a configuration is that as lamps become smaller (lower power consumption), the proportion of heat loss (including electrode loss) at the end of the arc tube in the lamp power inevitably increases. However, the purpose is to reduce this as much as possible and to suppress the decrease in lamp efficiency due to the miniaturization of the lamp.The second reason is to simplify the structure of both ends of the arc tube 1 to make the lamp larger. This is to reduce the manufacturing cost of. In fact, the inventors prototyped a high-pressure sodium lamp with an average color rendering index Ra of 75 or more using a single-crystal alumina tube and adopting the configuration shown in Figure 1.
The 50W lamp achieved a high lamp efficiency of 45m/W. This is a configuration that has been commonly used in conventional lamps, that is, an electrode or electrode conductor is sealed at the end of the arc tube through an end cap made of polycrystalline alumina, and the same tube wall. The maximum lamp efficiency of a 50W high color rendering high pressure sodium lamp consisting of an arc tube designed and prototyped according to the load is 37m/
This is significantly higher than W. Therefore, it can be said that this lamp, together with the excellent light color that this lamp originally has, has ample potential to replace incandescent light bulbs indoors, especially in stores and general homes.

However, in a small lamp equipped with an arc tube having such a configuration, in some cases, within a short period of time after the lamp is lit, the sealing process between the arc tube 1 and the electrode conductors 2 and 3 occurs during the manufacturing stage of the arc tube. At this stage, the sealed end of the arc tube 1 with the electrode conductors 2 and 3 cracks, which often leads to a serious situation where the sealed gas (Xe, Ne, Ar, etc.) leaks and the lamp cannot be lit. . The cause of such cracks is the presence of distortions and minute cracks that remain in the end of the single crystal alumina tube of the arc tube 1.
Directly, internal stress remaining in the sealing cement 4, 5 that is heated and melted when the electrode conductors 2, 3 are sealed,
When the lamp is lit, thermal stress is triggered by heat conduction from the discharge arc to the end of the arc tube 1 via the electrodes 6 and 7 and the electrode conductors 2 and 3. Even with current or near-future manufacturing and cutting technology for single-crystal alumina tubes, it is extremely difficult to completely eliminate distortions and minute cracks that remain at these ends.

An object of the present invention is to provide a high-pressure discharge lamp that can prevent a cracking accident of a single-crystal alumina arc tube during manufacturing of the high-pressure discharge lamp or during lamp operation. This is the purpose.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows the structure of the arc tube of a 50W high color rendering high pressure sodium lamp according to the present invention. As shown in the figure, the high-pressure sodium lamp according to the embodiment of the present invention includes a single-crystal alumina arc tube 1 with an inner diameter of 4.1 mm, and niobium tubes 9 and 10, which are electrode conductors, each holding electrodes 6 and 7 at their tips. It is equipped with The end of the arc tube 1 consists of a vicinity of the end face and an inner part located inside the vicinity of the end face. The niobium tubes 9 and 10 have large diameter parts 11 and 1 with an outer diameter of 4.0 mm.
2 and small diameter portions 13 and 14 having an outer diameter of 3.0 mm are formed, respectively. The large diameter portions 11 and 12 of the niobium tubes 9 and 10 are sealed to the inner surface of the inner portion of the arc tube 1 with sealing cements 4 and 5, respectively, and the small diameter portions 13 and 14 and the inner surface of the arc tube 1 near the end surface are sealed. A gap is provided between the entire inner surface. When sealing the arc tube 1 and the large diameter portions 11 and 12 of the niobium tubes 9 and 10, the sealing cements 4 and 5 that are heated and melted seal the large diameter portions 11 and 12 of the niobium tubes 9 and 10 due to their capillarity. ,1
0.05mm formed by 2 and the inner surface of arc tube 1
It flows into a very narrow cylindrical gap and fixes the two, and does not flow into the end surface of the arc tube 1 or the inner surface near this end surface.

Inside the arc tube 1, a mixed gas of neon and argon or xenon gas is sealed together with the sodium amalgam 8 as a starting or buffer gas. Furthermore, on the outer peripheral surface of both ends of the arc tube 1,
Thermal protection films 15 and 16 made of tantalum are attached, and when the lamp is operating, heat and light radiated from the inside of the arc tube 1, especially the electrodes 6 and 7, are transferred to the niobium tubes 9 and 10 behind the electrodes and the arc tube 1. It functions to confine the coldest spot in the tube existing at the boundary of the sealed portion and increase the temperature of this coldest spot. Therefore, the sodium vapor pressure inside the arc tube 1 is increased, and sodium D
Due to the self-reversal of the lines and the increased spectral line width in the entire visible range, this lamp can achieve a higher color temperature and better color rendering than ordinary high-pressure sodium lamps. The sodium vapor pressure inside the arc tube 1 can be adjusted over a fairly wide range by adjusting the lengths of the thermal protection films 15 and 16 in the longitudinal direction of the arc tube 1.

As described above, according to the embodiment of the present invention, the large diameter parts 11 and 12 of the niobium tubes 9 and 10 are sealed to the inner surface of the inner part of the arc tube 1 with the sealing cements 4 and 5, and the small diameter parts Since a gap is provided between the sealing cements 13 and 14 and the inner surface near the end surface of the arc tube 1, contact between the sealing cements 4 and 5 and the end surface and the inner surface near the end surface of the arc tube 1 is avoided. Therefore, even if a slight strain or minute crack remains on the end face of the single crystal alumina arc tube 1 or in the vicinity of this end face, the stress remaining on the sealing cement 4 and 5 after melting and fixation will be reduced, and the lamp lighting will be affected. It is possible to completely prevent the occurrence of cracks at and near the end surfaces of the arc tube 1, which would be caused by the thermal stress generated during the process.

In this example, for the arc tube 1 having an inner diameter of 4.1 mm, the small diameter portions 13 of the niobium tubes 9 and 10
The outer diameter of 14 is 3.0mm, and the gap between them is 0.55mm.
As described above, the melting conditions of the sealing cement due to the capillary phenomenon depend not only on the size of the gap but also on the properties of the sealing cements 4 and 5, and furthermore on the type of metal used as the electrode conductor. However, in order to prevent the sealing cements 4 and 5 from melting and fixing on the end face of the arc tube 1 and the inner surface in the vicinity thereof, it is preferable that the size of the gap is 0.2 mm or more.

Furthermore, according to the present invention, the following effects can be obtained. The function of the thermal protection films 15 and 16 attached to the outer peripheral surface of both ends of the arc tube 1 shown in FIG. 2 is as already explained. According to the present invention, the surface area of the niobium tubes 9 and 10 and the cross-sectional area of a portion thereof are smaller than those of the conventional arc tube 1 (FIG. 1). Therefore, heat loss due to thermal radiation and thermal conduction at both ends of the arc tube 1 during lamp operation is also reduced compared to the conventional lamp, and the temperature at the coldest point is increased. Therefore, for the reasons already mentioned, the lengths of the thermal protection films 15 and 16 in the longitudinal direction of the arc tube in order to achieve a predetermined lamp light color, that is, a predetermined sodium vapor pressure inside the tube, are as shown in FIG. It can be made shorter than in the case of an arc tube with a different configuration. Since the thermal protection films 15 and 16 are originally intended to shield light from the discharge arc within the arc tube 1, a reduction in their length directly leads to an increase in the total luminous flux of the lamp. For a 50W high color rendering sodium lamp equipped with the arc tube 1 shown in Figure 2, approximately 3
We saw an improvement in m/W. That is, the high-pressure discharge lamp according to the present invention has the effect of increasing lamp efficiency in addition to the effect mentioned at the beginning.

Figure 3 shows another configuration of the arc tube of the 50W high color rendering high pressure sodium lamp according to the present invention, which differs from the one in Figure 2 only in the configuration of the niobium tube and is otherwise completely the same. be. In this case, the niobium tubes 17 and 18 have large diameter portions 19 and 20 and small diameter portion 2.
1 and 22, which is the same as that shown in FIG. 2, but the difference is that the end portions also have separate large diameter portions 23, 24. Like the one shown in FIG. 2, the one shown in FIG. 3 also has the above-mentioned effect.

In each of the above embodiments, a niobium tube is used as the electrode conductor, but a tantalum tube, a zirconium tube, a titanium tube, a molybdenum tube, etc. may be used as appropriate.

Furthermore, the present invention can be applied not only to high-pressure sodium lamps but also to high-pressure discharge lamps such as metal halide lamps.

As explained above, the high-pressure discharge lamp of the present invention includes a translucent single-crystal alumina arc tube with an end portion near the end face and an inner portion located inside the end face vicinity, and an electrode held at the tip end. The electrode conductor has a large diameter portion and a small diameter portion, and the large diameter portion is sealed to the inner surface of the inner portion of the arc tube with sealing cement, and the electrode conductor is provided with a large diameter portion and a small diameter portion. A gap is provided between the small diameter portion of the conductor and the inner surface near the end face of the arc tube, so when sealing the arc tube and the electrode conductor, the end face of the arc tube and this The sealing cement does not melt and stick to the inner surface of the adjacent arc tube, and the accidents that have frequently occurred in the past, such as arc tubes cracking during arc tube manufacturing or lamp lighting, can be completely prevented.
Furthermore, lamp efficiency can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an arc tube of a high-pressure sodium lamp previously proposed, and FIGS. 2 and 3 are longitudinal sectional views of an arc tube of a high-pressure sodium lamp according to an embodiment of the present invention. 1... Arc tube, 4, 5... Sealing cement, 6, 7...
Electrode, 9, 10, 17, 18... Niobium tube, 11,
12, 19, 20...large diameter part, 13, 14, 21,
22... Small diameter part.

Claims (1)

[Claims] 1. A translucent single-crystal alumina arc tube having an end portion near the end surface and an inner portion located inside the vicinity of the end surface, and an electrode conductor holding an electrode at the tip portion, the electrode conductor having a diameter. A large diameter part and a small diameter part are formed, and the large diameter part is sealed to the inner surface of the inner part of the arc tube with sealing cement, and the small diameter part of the electrode conductor and the small diameter part near the end surface of the arc tube are sealed to the inner surface of the inner part of the arc tube. A high-pressure discharge lamp characterized by having a gap between the lamp and the inner surface.