JPS6362866B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a small metal halide lamp of 100 watts or less. [Technical background of the invention and its problems] Recently, from the viewpoint of power saving, technological development has been progressing to use metal halide lamps with excellent luminous efficiency in place of conventional incandescent lamps. Publication No. 54-63567 is known. In order to enable metal halide lamps to be used in place of incandescent light bulbs, metal halide lamps must be made smaller, and metal halide lamps with a power of 100 watts or less are required. In order to make this type of small metal halide lamp small in size and highly efficient, the arc tube is formed into a spherical or elliptical shape to activate vapor convection within the tube and improve its pressure resistance. However, due to its small size, the electrode is also small and the height of the electrode protruding into the arc tube is also small. If the protruding height of the electrode is low, the arc tube wall near the electrode, that is, quartz, is heated by radiant heat from the electrode bright spot and conductive heat from the electrode axis. It is known that when quartz glass is heated to about 1100° C. or higher, it tends to react with metal halides, particularly rare earth metal halides, producing, for example, silicon iodide (SiI ₄ ). This silicon iodide adheres to the vicinity of the electrodes and evaporates rapidly after the lamp is started, but its vapor pressure is so high that it generates a high restriking voltage during warming up, causing the lamp to turn off.
Furthermore, if the metal halide sealed in the arc tube reacts with the quartz glass as described above, the absolute amount of metal halide in the arc tube will be insufficient, leading to a decrease in luminous flux maintenance rate and deterioration of life characteristics. For this reason, it is conceivable to increase the height of the electrode protrusion to suppress the heating of the quartz glass near the electrode, but if the protrusion amount of the electrode is made too large,
The coldest part is formed at the back of the electrode, and the temperature of this coldest part becomes too low to promote evaporation of the metal halide, resulting in a decrease in luminous efficiency. [Object of the Invention] The present invention has been made based on the above-mentioned circumstances, and its purpose is to suppress the rise in restriking voltage to prevent extinction, and to increase the luminous flux maintenance rate and luminous efficiency. The aim is to provide a small metal halide lamp that can. [Summary of the Invention] The present invention provides a small metal halide lamp,
The shape of the arc tube is spherical, ellipsoidal, or close to it, the protrusion length of the electrode into the arc tube is l (mm), and the shortest distance between the electrode tip and the wall of the arc tube is d.
(mm), and is characterized in that these relationships are regulated so that the above objective can be achieved. [Embodiment of the Invention] Details of the present invention will be described below with reference to an illustrated embodiment. FIG. 1 shows an arc tube in a small metal halide lamp of 100 W (watts) or less, and this arc tube is usually housed in an outer bulb (not shown) to have a double tube structure. Reference numeral 1 denotes an arc tube made of quartz glass, which is formed into an elliptical spherical shape, and a pair of electrodes 2 and 3 are provided opposite to each other at both ends. The shape of the inner surface 1a of both ends of the arc tube 1 (the inner surface shape of the sealed portion of the electrodes 2 and 3) is formed into a shape with a larger curvature than the original ellipsoidal shape (the broken line portion). These electrodes 2 and 3
These have a known structure in which a tungsten electrode coil is wound around a tungsten electrode shaft. Metal foil conductors 6 and 7 made of molybdenum or the like are sealed in the sealed parts 4 and 5 of the arc tube 1, and the electrode shafts of the electrodes 2 and 3 are connected to these metal foil conductors 6 and 7, respectively. ing. These metal foil conductors 6 and 7 are connected to outer wells 8 and 9. The arc tube 1 is filled with a predetermined amount of mercury, a metal halide such as scandium-sodium iodide (ScI ₃ -NaI), and a starting rare gas such as argon. Such a substance is sealed through an exhaust pipe (not shown) extending from the side wall of the arc tube 1, and a tip-off portion 10 is formed by sealing off the exhaust pipe. Further, the arc tube is the arc tube 1 of the electrodes 2 and 3.
When the length of the inward protrusion is L (mm), and the shortest distance between the electrode tip and the wall of the arc tube is d (mm), d≧1.5 (mm) and d/l≧0.6 should be satisfied. It is formed. Each condition of the arc tube having such a configuration is based on the experimental results of the present inventors, and the experimental results will be described in detail below. First, the contents in the arc tube were argon (Ar120 Torr) as a starting rare gas and scandium-sodium iodide as a metal halide, which were adjusted to 6.7 mg per 1 c.c. of arc tube inner volume and the same lamp voltage. Enclose the amount of mercury, d
We prototyped lamps with various changes in the shortest distance between the electrode tip and the wall of the arc tube, and investigated the relationship between the lamps and the restriking voltage. Figure 2 shows the results, where the horizontal axis represents d;
The vertical axis shows the restriking voltage Vrs after 1000 hours of lighting. Note that Vrs is a measured value using a ballast with a primary side of 100V and a secondary side of 240V, and the turn-off voltage is 280~
It is around 300V. From Fig. 2, the area in which extinction does not occur due to the rise in restriking voltage even after 1000 hours of use is d
It can be seen that the range is ≧1.5mm. As mentioned above, if the quartz arc tube wall is too close to the electrode tip, that is, if d is smaller than 1.5 mm, the quartz glass will be heated to over 1100°C, and the quartz and scandium -It causes a reaction with sodium iodide, producing silicon iodide and increasing the restriking voltage. Therefore, if the shortest distance d between the electrode tip and the wall of the arc tube is set to 1.5 mm or more, the quartz glass will not be heated above 1100°C, and it will be possible to prevent the quartz glass from turning off due to an increase in the restriking voltage. it is conceivable that. In addition, the reaction between quartz and luminescent metal iodide due to overheating of quartz glass to produce silicon iodide means that at least a portion of the metal iodide is reduced to metal. Since it is more difficult to evaporate than the iodide of the metal, it is natural that the effective amount of luminescent metal (amount of evaporation) in the arc tube when the lamp is lit.
decreases, and the luminous flux decreases. That is, the second
Looking at the light speed maintenance rate after 1000 hours of use for the lamps with each d value shown in the figure, the lamps with d≧1.5mm all had a rate of 80% or more, while the lamps with d<1.5mm had a rate of 40%. % to 50%, which was a huge drop. Further, when d was less than 1.5 mm, it was observed that tungsten, the electrode constituent material, was scattered and adhered to the inner surface of the arc tube near the electrodes, resulting in blackening. Next, find the shortest distance d between the electrode tip and the arc tube wall.
In order to set the diameter to 1.5 mm or more, the inner shape of both ends of the arc tube 1, that is, the inner shape of the sealed portion of the electrodes 2 and 3, is determined. FIG. 3 is a schematic diagram of one end of the arc tube of a prototype lamp for experimentation conducted to find the optimal structure of the arc tube shape. The shape of the main part of the arc tube is small as mentioned above, and in order to obtain high luminous efficiency, it is formed into a spherical, elliptical, or similar shape to activate the convection of steam within the tube. . FIG. 3 shows an example of an ellipsoidal shape. Figure a shows an ellipsoidal arc tube formed into the original ellipsoidal shape without damaging the shape of the inner surface 1a of the end, and figure b shows the shape of the inner surface 1a of the end of the arc tube (the inner surface shape of the electrode sealing part). It is formed to have a larger curvature than the original inner surface shape of the end portion of the elliptical sphere (the broken line portion), and a, b, and d are set to have the same length. Therefore, the electrode protrusion length l of b is shorter than that of a by Δl. On the other hand, the shape of the arc tube in figure c is exactly the same as that in a, but the shape of the inner surface 1a of the end portion is formed so as not to spoil the original elliptical spherical shape.
The electrode protrusion length l is set to be the same as b. Therefore, as shown in the figure, d is smaller than a and b. 30W (watts) of these various shapes of luminous tubes
The case where this is applied to a lamp will be described. For a, the arc tube is shaped like an elliptical sphere with a major axis of 10 mm and a minor axis of 4 mm, and the inside contains Ar120 Thor and Scandium.
Sodium iodide (ScI ₃ -NaI) was 4 mg, the distance between the electrodes was 4 mm, the electrode protrusion length l was 3 mm, and d was 1.5 mm. Regarding b, the difference from a is that the inner surface 1a of the end of the arc tube has a larger curvature than the inner surface of the ellipsoidal end (broken line), and the protruding length l of the electrode is 2 mm. Therefore, the arc tube becomes a modified ellipsoid with a long axis of 8 mm, but the value of d is the same as a.
It is 1.5mm. Furthermore, for c, l is 2 mm, the same as a, and it is an elliptical sphere with a major axis of 8 mm and a minor axis of 4 mm, and the distance between the electrodes is set to 4 mm, the same as a and b.
The value of d is 1.2 mm, which is smaller than that of a and b. In addition, the amount of mercury in a, b, and c is the same lamp voltage.
It has been adjusted to obtain 80V. The table below compares the results of measuring the characteristics of 10 lamps each of a, b, and c.

[Table] As can be seen from Table 1, in the case of a, the electrode protrusion length l is large, so the coldest point occurs behind the electrode, and the luminescent metal scandium-sodium iodide is insufficiently evaporated, resulting in poor efficiency and color rendering. Both genders are lower. In the case of c, since d (the shortest distance between the electrode tip and the arc tube) is smaller than 1.5 mm, the overheated quartz and iodide react as described above, causing an increase in the restriking voltage. This is thought to have an adverse effect on startup, efficiency, color rendering properties, and other life characteristics. Regarding c, we tried making a prototype lamp with a value of d greater than 1.5 mm by making the arc tube one size larger, but as the arc tube volume increased, the load on the tube wall decreased too much and the characteristics were insufficient. was not obtained. on the other hand,
In case b, it is as if the drawbacks of a and c are compensated for, and a lamp with excellent characteristics despite its small size can be obtained. Incidentally, the values d and d/l of the lamps a, b, and c are as follows.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to obtain a small metal halide lamp that suppresses the rise in restriking voltage and prevents the lamp from going out, and has excellent luminous flux maintenance rate and luminous efficiency.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of the arc tube of a small metal halide lamp which is an embodiment of the present invention, and Figure 2 shows the relationship between (the shortest distance between the electrode tip and the wall of the arc tube) d (mm) and the restriking voltage. FIG. 3 shows a vertical cross-section of one end of various experimental arc tubes. 1... Quartz arc tube, 1a... Arc tube end inner surface,
2, 3... Electrode, l... Electrode protrusion length, d... Shortest distance between the electrode tip and the arc tube wall.

Claims (1)

[Scope of Claims] 1. A small metal halide lamp of 100W or less, which has an arc tube made of a quartz bulb with a pair of opposing electrodes and a starting rare gas, mercury, and metal halide sealed inside. The shape of the arc tube is spherical, ellipsoidal, or similar, and the length of the electrode protruding into the arc tube is l.
(mm), the shortest distance between the electrode tip and the arc tube wall is d
(mm), d≧1.5 (mm) d/l≧0.6.