JPS641904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal halide lamp used with a tube power of 700 W to 1 kW.

Recently, metal halide lamps have come to be lit using mercury lamp ballasts, that is, single-yoke coil ballasts, but in this case, special measures are required because metal halide lamps have a higher starting voltage than mercury lamps. are doing. As an example, the starting auxiliary resistor connected to the starting auxiliary electrode has a low resistance value of about 50 to 100 Ω, and during starting, the starting auxiliary electrode and the nearby main electrode are connected to each other. A method has been developed in which a starting arc discharge is caused between the electrodes, and then an arc discharge is caused between the opposing main electrodes.

However, such starting lighting means is limited to low-load lamps with a tube input of 250 W to 400 W, and cannot be applied to high-load lamps with a tube input of 700 W to 1 kW. This means that for conventional 700W to 1kW high-load lamps, the inner diameter of the arc tube
The distance between the electrodes is relatively small at 22mm to 25mm, and the potential gradient is small compared to this, so the starting voltage is high and the transition from starting arc discharge to main arc discharge cannot be performed smoothly. There is.

This invention was made based on these circumstances, and its purpose is to
The purpose of this project is to provide a metal halide lamp that increases the potential gradient of a 1 kW lamp, improves startability, and improves luminous efficiency, that is, brightness.

In other words, this invention aims to increase the potential gradient by reducing the distance between the electrodes to improve startability, and at this time, to prevent an increase in the load on the tube wall, the inner diameter of the arc tube is made thicker, and the inner diameter of the arc tube is increased. It features a metal halide lamp that allows for improved brightness based on the metal halide lamp.

An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram of a lighting circuit for a metal halide lamp, and numeral 1 indicates an arc tube. The arc tube 1 has a bulb 2 made of a right-handed English glass tube, with both ends crushed and sealed, and a pair of main electrodes 3a and 3b are provided inside the bulb 2, facing each other. Inside this valve 2, an auxiliary starting electrode 4 is provided adjacent to one main electrode 3a. In addition, 5a, 5b, and 6 are metal foils, such as molybdenum, and are sealed in the sealing part. The starting auxiliary electrode 4 includes a starting auxiliary resistor 7 and a bimetal switch 8 as a thermally responsive switch.
are connected in series so as to have the same polarity as the other main electrode 3b. The arc tube 1 is filled with a starting rare gas consisting of neon gas (Penning gas), which is a mixture of mercury, metal halides such as scandium iodide and sodium iodide, and, for example, 1% krypton. Furthermore, the distance between the electrodes in the arc tube 1 is assumed to be L, and the tube inner diameter is assumed to be d.

The arc tube 1 as described above is housed in an outer tube 9 together with the auxiliary starting resistor 7 and the bimetal switch 8. When in use, it is connected to a power source 11 via a single yoke coil type ballast 10.

Since the bimetal switch 8 of such a metal halide lamp is closed before starting, when the lamp is connected to the power source 11, a voltage is applied between one main electrode 3a and the auxiliary starting electrode 4 adjacent thereto. At this time, the starting auxiliary resistor 7 has a resistance value of
Since the resistance is as low as 50Ω to 100Ω, a large current flows to the auxiliary starting electrode 4, and although a glow discharge is initially generated between the auxiliary starting electrode 4 and the main electrode 3a, the auxiliary current is generated instantly. Causes arcing. This auxiliary arc discharge generates a high density of electrons in the arc tube 1, and these electrons are transferred to the main electrodes 3a and 3b.
Since the space between the main electrodes 3a and 3b is ionized, main arc discharge occurs between the main electrodes 3a and 3b. The arc tube 1 generates heat due to this main arc discharge, and this heat opens the bimetal switch 8 to maintain normal lighting of the lamp.

The following experiments were carried out on a metal halide lamp lit by the above-mentioned action. In a metal halide lamp with a power supply voltage of 200 V and a tube input rating of 1 kW, the inner diameter d of arc tube 1 is
By keeping the distance L constant at 25 mm and varying the distance L between the electrodes,
When we investigated the lighting probability, we obtained the results shown in Figure 2.

In other words, what can be seen from Figure 2 is that 200V, 1kW
When the inner diameter d of the arc tube is 25 mm in a rated metal halide lamp, the distance L between the electrodes is
If it is less than 100mm, the probability of lighting will be approximately 90%,
This means that if L is 90 mm or less, the lighting probability reaches 100%.

By the way, the potential gradient is the voltage applied to the arc tube.
It is the value obtained by dividing V ₀ by the distance L between the electrodes (V ₀ /L),
Therefore, the potential gradient can be plotted on the horizontal axis in FIG. 2 above. In this case, since the tube voltage V ₀ is the average effective value of the power supply voltage that has been dropped by the ballast 10 and resistances such as lead wires, the voltage drop is assumed to be 10%, and the applied voltage waveform is sinusoidal. Since waves are used, V _L = 180×
√2=254.6 (V). Therefore, the potential gradient is
254.6/L (V/cm), 25.5V/cm when L=100mm=10cm, 28.3V/cm when L=9cm
becomes. Therefore, in Figure 2, the potential gradient is
If the voltage is 25.5V/cm or more, the probability of lighting is 90%,
In other words, if the voltage is 28.3V/cm or higher, the lighting probability is 100%.

Note that the lighting probability is targeted to be 90% or more in a low-load lamp, so if it is 90% or more, the object of the present invention is achieved.

By the way, even if the lamp starts reliably, when the rated input is applied to the lamp to turn it on, if the load on the tube wall becomes extremely large, the quartz glass that makes up the arc tube bulb will deteriorate, causing the quartz to break. It is a danger. It has been confirmed that lamps with the characteristics shown in Figure 2 will break down during a lighting life of approximately 9000 hours if the tube wall load exceeds 17 W/cm ^{2 .} It is known not only from the above-mentioned experiment, but also from the past, that it is necessary to suppress the amount below. Therefore, if the tube wall load is to be regulated to 17 W/cm ² or less, the distance L between the electrodes must be 75 mm or more in the characteristic diagram shown in Figure 2. In other words, the potential gradient must be
This means that it needs to be below 33.9V/cm.

By the way, the tube wall load is determined by the tube input (W) and the distance between the electrodes.
(L) and the pipe inner diameter (d) (W/πd _L ), so the pipe wall load when the pipe input is 1 kW is determined by the relationship between the interelectrode distance (L) and the pipe inner diameter. It is shown in FIG. It can be seen from this figure that the pipe inner diameter d is 21.2 mm in the range where the pipe wall load is 17 W/cm ² or less.
This includes those with an inter-electrode distance L of 100 mm, but
The starting characteristics, the luminous flux maintenance rate, and the total luminous flux indicated by diagonal lines in the figure do not all satisfy the good range, and the lighting probability, that is, the starting performance is poor, which does not meet the object of the present invention. The reason for this is thought to be that as the inner diameter of the arc tube becomes smaller, the loss of electrons at the tube wall becomes more significant. Furthermore, as you can see from Figure 3, the inner diameter of the pipe is 35mm.
Those in which the distance between the electrodes exceeds 100 mm do not meet the purpose of the present invention. Therefore, from these values, the minimum value of the tube wall load is expressed as 9.1 W/cm ² .

On the other hand, if the distance L between the electrodes is too short, that is, if the potential gradient is too large, the luminous flux maintenance factor will drop significantly. That is, when the relationship between the inter-electrode distance L and the luminous flux maintenance factor was investigated with a tube input of 1 kW and a tube wall load of 15 W/cm ² after lighting for 1000 hours, the results shown in FIG. 4 were obtained. It can be seen that as the inter-electrode distance L becomes smaller, the luminous flux maintenance factor also tends to decrease, and this is because the tungsten constituting the electrodes evaporates and adheres to the tube wall, leading to early blackening. In other words, if the distance L between the electrodes is reduced, the evaporated tungsten will be transported uniformly and will be uniformly deposited on the transparent portion of the quartz glass. On the other hand, when the distance between the electrodes is long, the transport of evaporated tungsten occurs only locally;
Darkening also occurs only locally. and
Since the luminous flux maintenance rate after 1000 hours of lighting is required to be 80% or more, the distance between the electrodes is limited to 55 mm or more, and the potential gradient is limited to 46.2 V/cm or less.

Furthermore, when examining the relationship between the tube inner diameter d and the total luminous flux (lm) under horizontal lighting conditions with a tube input of 1 kW and a tube wall load of 15 W/cm ² , the characteristics shown in FIG. 5 were obtained.

For a 1kW input lamp, the total luminous flux is
Since 90000 lm or more is required, the pipe inner diameter d is
It should be regulated to 25mm or more and 35mm or less. This is because if the tube diameter exceeds 35 mm, the temperature of the coldest part will become too low in horizontal lighting, and the evaporation of the enclosed metal will not be promoted, resulting in a decrease in luminous efficiency, and if the tube inner diameter is smaller than 25 mm. It is presumed that this is due to a decrease in efficiency due to both a relative increase in loss at the tube wall and local concentration of luminescent metal due to a reduction in convection inside the arc tube.

For this reason, as shown by diagonal lines in Figure 3, the tube wall load should be 17 W/cm ² or less, and the tube inner diameter d should be 25 mm.
It can be seen that if the above value is 35 mm or less and the potential gradient is 25.5 V/mm or more and 46.2 V/mm or less, the lighting probability, that is, the startability, is improved, and the total luminous flux, that is, the brightness is increased. The above numerical characteristics mean that the tube inner diameter is larger and the distance between the electrodes is shorter than in the conventional case, and the characteristics shown in FIGS. 2 to 5 confirm this effect.

As explained above, the present invention has the advantage that the distance between the electrodes is shortened and the potential gradient becomes large, so starting performance is improved, and the inner diameter of the tube is increased, so the luminous efficiency is improved and the brightness is increased.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the lighting circuit of the lamp of the present invention, Fig. 2 is a characteristic diagram of lighting probability, Fig. 3 is a characteristic diagram of tube wall load, and Fig. 4 is a characteristic diagram of luminous flux maintenance factor.
FIG. 5 is a characteristic diagram of the total luminous flux. 1... Arc tube, 3a, 3b... Main electrode, 4...
Auxiliary electrode for starting, 7... Auxiliary resistance for starting, 8...
Bimetal switch, 9...outer tube.

Claims (1)

[Claims] 1 A pair of main electrodes are provided at both ends of the arc tube, and an auxiliary starting electrode is provided close to at least one of the main electrodes, and mercury, a metal halide, and a starting rare gas are sealed, and at the time of starting, A starting arc discharge is generated between one of the main electrodes and an auxiliary starting electrode adjacent thereto, and then a main arc discharge is generated between the main electrodes.
In metal halide lamps used with a tube input of 700W or 1kW, the tube wall load of the arc tube is reduced.
17W/ ^cm2 or less, inner diameter of arc tube 25mm to 35mm
and the potential gradient is 25.5V/cm or more 46.2V/cm
A metal halide lamp characterized by the above.