JPH0339380B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to measures for improving the luminous flux maintenance factor, starting voltage, and turning off voltage in metal halide lamps.

[Technical background of the invention and its problems]

Metal halide lamps have higher efficiency and color rendering properties than mercury lamps, so they are rapidly becoming popular as an energy-saving light source.Also, with the development of metal halide lamps that can be started with high-pressure mercury lamp ballasts, it is expected that Further spread is expected.

However, although metal halide lamps have superior properties such as high color rendering and high efficiency compared to mercury lamps, they have disadvantages in that they are inferior in starting voltage, turning off voltage, and luminous flux maintenance rate. This is because metal halide lamps usually use at least one of the halides of alkali metals, alkaline earth metals, and rare earth metals as the light-emitting metal, and these halides provide high color rendering and high efficiency; This is the cause of poor startability and working speed.

In particular, when rare earth metal halides, such as scandium (Sc) halide, are used as the metal halide, the luminous flux maintenance factor is at a low level because the rare earth metal has strong reactivity. The reason for this is presumed to be the following phenomenon. That is,
In rare earth metal halides, the rare earth metal and halogen are separated based on the halogen cycle, and this liberated halogen combines with silicon (Si) as the material of the arc tube to produce silicon halide, which adheres to the tip of the electrode. A low contact point alloy of Si and W is formed, and this alloy adheres to the wall of the arc tube by ion bombardment and turns black, absorbing visible light and causing a decrease in luminous flux. Furthermore, due to the reaction and scattering of Si and W, the shape of the tip of the electrode is significantly deformed, causing instability of the arc bright spot, resulting in an increase in starting voltage and turning off voltage.

In order to eliminate such problems, conventionally, rare earth metal is sealed in the arc tube in a larger amount than the halide, that is, metal rich, and the halogen liberated during the halogen cycle is captured by the excess rare earth metal. It is known that this was done. However, if an excessive amount of rare earth metal is simply filled into the arc tube, a thin film of rare earth metal will adhere to the wall near the coldest part of the arc tube, and this thin film will block visible light and significantly reduce the luminous flux. A phenomenon is observed.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a metal halide lamp with improved luminous flux maintenance factor, starting voltage, and turning-off voltage.

[Structure of the invention]

In the present invention, in an arc tube equipped with a pair of main electrodes,
In a metal halide lamp in which mercury, a starting rare gas, and at least one type of rare earth metal halide are sealed, and the rare earth metal is attached to the main electrode, the rare earth metal has an operating temperature of 1350°C to 1800°C in a stable operating state at the main electrode. It is characterized by adhering to areas with temperatures in the range of ℃.

[Effect]

According to the present invention, since the rare earth metal is attached to the main electrode, the rare earth metal diffuses and covers the electrode, thereby preventing scattering of the electrode material and the electron emitting material. In addition, the rare earth metal covering the electrode prevents the reaction product of free halogen and silicon from touching the electrode due to the capture of free halogen due to the halogen cycle, and the formation of a low melting point metal between silicon and tungsten. In addition to preventing
Suppresses tungsten evaporation and prevents sputtering caused by ion bombardment. This prevents tungsten from scattering and adhering to the tube wall. Moreover, the operating temperature of the main electrode of rare earth metals is
Since it is installed in a location where the temperature ranges from 1350℃ to 1800℃, diffusion is performed smoothly, and the rare earth metal in the discharge space reliably returns to this location, ensuring that the rare earth metal covers the electrode. It will be done.

[Embodiments of the invention]

The present invention will be explained in detail below based on an embodiment shown in FIGS. 1 to 6.

In the figure, reference numeral 1 indicates an outer tube, and within this outer tube 1 is accommodated a luminous tube 2 made of quartz glass. Inside the arc tube 2, a pair of main electrodes 3a, 3b and an auxiliary starting electrode 4 are arranged close to one of the main electrodes 3a. Note that there is also a type in which the auxiliary electrode 4 is not used depending on the situation.

The arc tube 2 is filled with a predetermined amount of mercury, a starting rare gas such as argon gas, and a luminescent metal containing at least one rare earth metal halide such as ScI ₃ and NaI.

The arc tube 2 has both ends attached to holders 5a and 5b.
are held by supports 6a and 6b, respectively, with one support 6a being welded to an inner conductor 8a sealed to the stem 7, and the other support 6b being attached to the top of the outer tube 1. There is. One main electrode 3a of the arc tube 2 is electrically connected to one support 6a, and the other main electrode 3b is connected to a connecting wire 10 via a lead wire 9, and this connecting wire 10 is connected to the stem. 7 and is connected to another inner conductor 8b which is sealed. The one inner conductor 8b is connected to the base 11, and
The other inner conductor 8b is connected to the eyelet terminal 1 of the base 11.
Connected to 2.

On the other hand, the starting auxiliary electrode 4 is connected to the connecting line 10 via a starting auxiliary resistor 13 and a normally closed bimetal switch 14.

And on one support 6a there is a glow lighting tube 1.
5 is attached via a lighting tube holder 16. One of the pair of lead wires 17a, 17b led from this glow lighting tube 15, 17a
is connected to the support 6a, and the other lead wire 17b is connected to one end of the current limiting resistor 18. The other end of this current-limiting resistor 18 is connected to a connection portion between the bimetal switch 14 and the starting auxiliary resistor 13.

Therefore, the lighting tube 15, the current limiting resistor 18, and the bimetal switch 14 form a series circuit as shown in FIG. It is something that exists.

Therefore, the main electrode 3 provided inside the arc tube 2
a and 3b are constructed as shown in FIG. That is, although FIG. 3 shows one main electrode 3a as a representative, the main electrode 3a has an electrode coil 3 made of tungsten on an electrode shaft 30 made of tungsten or tungsten containing thorium Th.
1 is wrapped. Although the electrode coil 31 is a two-layer coil, this electrode coil may be a single-layer or double-layer coil. The electrode coil 31 has an operating temperature of at least 1350°C during stable operation.
Rare earth metal 32 consisting of scandium etc. is placed in the area where the temperature ranges from 1800℃, for example at the outermost edge.
is attached by means such as vapor deposition or thermal spraying.

Note that nitrogen gas or a mixed gas of nitrogen gas and other inert gas is contained in the outer tube 1, for example.
Approximately 400 torr is enclosed. Also, current limiting resistor 18
is set to a resistance value of approximately 300Ω.

The operation of the embodiment having such a configuration will be explained.

As shown in FIG. 2, the lamp is connected to a power source 20 via a mercury lamp ballast 19, but since the normally closed bimetal switch 14 is closed at the time of starting, this switch 14 is current limited. A current flows through the resistor 18 and the glow lamp tube 15.
In the glow lighting tube 15 described above, the glow current heats the bimetal inside the lighting tube 15 and opens and closes the lighting tube contacts, thereby disconnecting the ballast 19 via the current limiting resistor 18. . The ballast 19 generates a pulse voltage due to the fluctuation of this blockage current, and this pulse voltage is applied between the starting auxiliary electrode 4 and one of the main electrodes 3a adjacent thereto, and between the two main electrodes 3a, 3.
Administered between b. Therefore, the arc tube 2 will start.

When the arc tube 2 starts, the bimetal switch 14 is heated by the heat from the arc tube 2 and opened, thereby opening the DC circuit and preventing current from flowing through the lighting tube 15 and the current limiting resistor 18. and auxiliary electrode 4
and the main electrode 3a are kept at the same potential.

In the metal halide lamp operated as described above, a rare earth metal such as scandium metal 32 is attached to the electrode coil 31, so that this scandium metal 32 is diffused during lighting and is attached to the electrode shaft 31.
0, and as the electrode temperature decreases, the work function at the tip of the electrode shaft 30 is lowered, suppressing the evaporation of tungsten, and promoting the reduction of sputtering due to ion bombardment.
In other words, the deformation of the arc bright spot is reduced. As a result,
Prevents rise in starting voltage and turning off voltage.

Further, the scandium metal not only captures free halogen through the halogen cycle and prevents the free halogen from reacting with silicon (Si) of the arc tube material, but also prevents the scandium metal 32 attached to the electrode coil 31 from diffusing. Since it covers the electrode coil 31 of the lever, it prevents the silicon halide from coming into direct contact with the tip of the electrode, which also prevents the reaction between silicon and tungsten.
Tungsten is less likely to fly off and adhere to the electrode.

As a result, evaporation of the tungsten, sputtering, and scattering of the tungsten are reduced, blackening of the tube wall is reduced, and the luminous flux maintenance factor is improved.

Moreover, scandium metal 32 is electrode coil 3
Since it is attached to 1, scandium metal 3
The proportion of the scandium metal 32 that directly adheres to the tube wall is reduced, which reduces the proportion that the scandium metal 32 itself blocks visible light, contributing to an improvement in the luminous flux maintenance rate.

Figures 4 to 6 show scandium metal 3
The results of examining the changes in luminous flux maintenance factor, starting voltage, and turning-off voltage are shown for cases in which No. 2 was attached to the tip of the electrode coil 31 and those where No. 2 was not attached. The lamps used were ScI ₃ and NaI.
These are 400W metal halide lamps, and the solid line A shows the lamp of this embodiment as shown in FIG. 3, and the broken line B shows the conventional lamp. In the luminous flux maintenance factor characteristics shown in FIG. 4, there is not much difference at the initial stage of use, but it can be seen that the lamp of this embodiment becomes more advantageous as the usage time progresses. Furthermore, in the starting voltage characteristics shown in FIG. 5, it is recognized that the lamp of this example maintains the starting voltage lower than that of the conventional lamp even after the usage time has elapsed. Furthermore, it can be seen that the turning off voltage in FIG. 6 shows a difference in that the turning off voltage of the lamp of this embodiment is lower than that of the conventional lamp with the passage of time of use.

In addition, the temperature at which rare earth metals are attached is 1350℃ or higher.
The reason why a temperature range of 1800°C is desired is as follows.
In other words, in order for the rare earth metal attached to the electrode to diffuse and cover the electrode, it must return to the electrodes 3a and 3b without adhering to the wall of the arc tube 2. Recurrence requires a location with a temperature of 1350°C or higher because it returns to a location with a high temperature. Note that 1350℃ is an empirical value. Also, locations where the temperature is higher than 1800°C are undesirable because the rare earth metal itself evaporates and adheres to the tube wall.

By the way, in Figure 3, the electrode temperature distribution of a 400W class metal halide lamp is around 1600℃ at the tip of the coil (approximately l ₁ ), and around 1600℃ at the rear end of the coil (approximately
l ₂ ) is around 1300° C. Therefore, it is effective to attach the rare earth metal to the outer surface of the first turn of the tip of the coil 31.

Also, among rare earth metals, scandium is the most frequently used, and when scandium halide is used as a light-emitting metal, scandium metal is the most suitable rare earth metal to be attached to the electrode. The rare earth metal of the electrode is effective regardless of the combination of materials.

Furthermore, when attaching the rare earth metal of the electrode, as shown in FIGS. 7 and 8, the rare earth metal piece 7
0 may be sandwiched within the electrode coil 31, between coils, etc.

〔Effect of the invention〕

As detailed above, in the present invention, a rare earth metal is attached to the main electrode, so that the rare earth metal covers the electrode, lowering the work function of the electrode, preventing sputtering due to ion bombardment, and freeing the rare earth metal. Because it captures halogens,
The luminous flux maintenance factor is improved, and the starting voltage and turning off voltage are reduced to improve starting performance. Moreover, since the rare earth metal is attached to the electrode, the proportion of the rare earth metal itself attached to the wall of the arc tube is reduced, which also has the advantage of reducing visible light shielding and improving luminous flux.

[Brief explanation of the drawing]

1 to 6 show an embodiment of the present invention, FIG. 1 is a configuration diagram of a metal halide lamp compatible with a ballast for a mercury lamp, FIG. 2 is a circuit diagram thereof, and FIG. 3 is a diagram showing electrodes. Figures 4 to 6 are characteristic diagrams,
FIG. 7 and FIG. 8 are diagrams of electrodes showing modified examples, respectively. 1... Outer tube, 2... Arc tube, 3a, 3b... Main electrode, 4... Auxiliary electrode for starting, 30... Electrode shaft,
31... Electrode coil, 32, 70... Rare earth metal.

Claims (1)

[Scope of Claims] 1. A metal halide lamp in which mercury, a starting rare gas, and at least one kind of rare earth metal halide are sealed in an arc tube equipped with a pair of main electrodes, and a rare earth metal is attached to the main electrodes, A metal halide lamp characterized in that the rare earth metal is attached to the main electrode at a location where the operating temperature in a stable operating state is in the range of 1350°C to 1800°C. 2. The metal halide lamp according to claim 1, wherein when scandium halide is used as the luminescent metal, the rare earth metal deposited on the main electrode is scandium.