JPH08180833A - Short arc metal halide lamp - Google Patents

Abstract

PURPOSE: To stabilize the emitting output, in a DC lighting short arc metal halide lamp suppressed in cloudiness, and provide a long-lived light source having an excellent characteristic as a light source for liquid crystal projection display by surely and stably forming an arc spot on the top end of a cathode. CONSTITUTION: In a short arc metal halide lamp having a cathode 1; an anode 2; and at least a rare earth halide sealed therein, and lighted by a DC power with an approximately horizontal discharging direction, the cathode 1 is constituted by winding a coil 10 on a tungsten shaft. When the sectional area of the tungsten shaft is set to Smm<2> , and the current at steady light is IA, the value obtained by dividing S by I is larger than 0.029 and smaller than 0.076.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for a display, and more particularly to a short arc metal halide lamp used as a light source for a liquid crystal projection display.

[0002]

2. Description of the Related Art Recently, short arc metal halide lamps containing rare earth halides such as dysprosium and neodymium, which have high efficiency and high color rendering properties, have been widely used as light sources for liquid crystal projection displays. This type of lamp is 35w / cm due to high brightness requirement.
^Since it is lit with a high load of about ² to 80 w / cm ² ,
Quartz tube There is a problem that the tube wall temperature reaches 900 ° C or higher, and white turbidity occurs on the tube wall after lighting for several hundred hours. When clouding occurs, in an application intended for optical application, the apparent light emitting area of the lamp becomes large, so that the light utilization efficiency is significantly deteriorated, and the cloud life practically determines the lamp life.

As a method of lighting a short arc metal halide lamp for a liquid crystal projection display, lighting by a rectangular wave having a frequency in the range of 250 Hz to 500 Hz is generally put into practical use, and one of methods for suppressing clouding is also provided. It has also been proposed to illuminate with direct current.
As already reported by the present inventors at the 1993 National Convention of the Lighting Society of Japan (lecture No. 24), it was found that the effect of suppressing white turbidity was remarkable when the discharge direction was set to be horizontal and the lighting was performed by direct current. When applying to a short arc metal halide lamp for a liquid crystal projection display, it was found that there are special measures to remove the color unevenness and obtain good characteristics as a light source for a liquid crystal projection display. .

[0004]

SUMMARY OF THE INVENTION The present invention provides a short arc metal halide lamp for direct current lighting in which white turbidity is suppressed, in order to reduce color unevenness to a minimum and to obtain efficient light emission. An object of the present invention is to stabilize a light emission output and realize a long-life light source having excellent characteristics as a light source for a liquid crystal projection display.

[0005]

The inventors of the present invention have invented a method of turning on DC power with the discharge direction horizontal as a method for suppressing the occurrence of white turbidity, as already filed for a patent. This is to positively utilize the bias phenomenon (a phenomenon called cataphoresis) of a light-emitting substance that occurs when a direct current is turned on, which is conventionally disliked, for suppressing white turbidity. That is, rare-earth ion atoms are pulled toward the cathode by direct current lighting,
As a result, a phenomenon occurs that the density of rare earth atoms from the cathode to the anode gradient, especially by the effect of continuously attracting ion atoms to the cathode, by reducing the number of rare earth ion atoms and neutral atoms reaching the tube wall, We succeeded in dramatically reducing the occurrence of cloudiness.

However, in the process of developing a practical lamp, it has been found that arc instability easily occurs in direct current lighting. It was found that the cause of the flickering of the arc was caused by the cathode and caused by the anode. As for the shape of the anode to be formed, it has been found that the area of the plane of the tip of the electrode shaft of the anode should be designed within a certain range with respect to the lamp current, as already applied for a patent. With respect to the cathode, the inventors of the present invention have found that, as a result of experiments, assuming that the lamp current is I ampere and the cross-sectional area of the cathode electrode axis is S mm 2, 0.029 <S / I <0.076.
It has been found that a stable discharge can be obtained by designing the electrode axis of the cathode so as to satisfy the above condition, and more preferably a good result can be obtained when the electrode protrusion length is twice or more the electrode axis. The configuration of the present invention will be described with reference to FIG.
A rare gas, mercury, and at least a rare earth halide and cesium halide are enclosed in a quartz arc tube 3 having a pair of tungsten electrodes that operate as a cathode 1 and an anode 2 at both ends. A short arc metal halide lamp for direct current lighting is constructed by encapsulating tin oxide. Here, 5 is a molybdenum foil embedded in the sealing portion 4, and 6 is an external lead rod connected to the foil 5. As shown in FIG. 2, the cathode has a shape in which a tungsten coil 10 is wound around an electrode shaft 15 mainly composed of tungsten. When the cross-sectional area of the cylindrical electrode shaft 15 is square millimeter and the rated lamp current is I ampere, 0 It is designed to satisfy the relationship of 0.029 <S / I <0.076, and the protrusion length L of the tip 11 of the electrode shaft 15 is twice or more the electrode shaft 15.

[0007]

It has been found that by defining the relationship between the lamp current and the cross-sectional area of the cathode shaft as described above, a cathode spot can be stably formed at the tip 11 of the cathode shaft 15 and a stable light emission output can be obtained. The effects of the present invention will be described with reference to examples.

[0008]

EXAMPLE A lamp having an input power of 125 W will be described as a first example. Inner diameter 7.5 mm, inner volume 0.3
A tungsten anode 2 and a cathode 1 were opposed to each other at a distance of 3 mm and sealed in a quartz arc tube 3 of ³ cm ³ . The cathode 1 is a tungsten shaft 1 having a diameter of 0.35 mm and a total length X of 8 mm.
Use a tungsten coil 10 having a diameter of 0.3 mm wound 4 turns on 5 and leave the tip 11 as a cut surface,
The tip 11 of the electrode shaft was projected from the coil 10 by 1.0 mm. That is, L = 1 mm. The anode 2 has a diameter of 1.
Using a cylindrical tungsten shaft having a length of 4 mm and a total length Y of 10 mm, the corners were cut off so that the diameter of the tip 12 was 0.4 mm, and the sealing portion 13 to the quartz glass had a diameter of 0.7 m.
What was ground to m was used. The arc tube 3 is evacuated, mercury 14 mg, a mixture of a rare earth halide containing dysprosium iodide and cesium iodide 0.4 mg, and indium iodide 0.3 mg are charged, and further, argon gas is charged at a pressure of 150 torr. did. A heat-resistant oxide was applied as a heat retaining film 32 on the outer surface 31 of the arc tube on the cathode side of the lamp.
When this lamp is lit with 125W DC input power, the lamp voltage becomes 68V, the lamp current is 1.84A and the efficiency is 6
4 lumen / W, color temperature 7350K (S / I =
0.052). Five lamps of this specification were manufactured and a lighting test was conducted. As a result, stable discharge was performed even after lighting for 2000 hours, and white turbidity and blackening did not occur, and good results were obtained.

On the other hand, in the lamp of this specification, the cathode shaft 1
Almost the same good results were obtained when the diameter of 5 was 0.3 mm (S / I = 0.038) and 0.4 mm (S / I = 0.68). However, when a lamp with a diameter of 0.5 mm was prototyped (S / I = 0.086) and a lighting test was performed, the cathode spot moved along the tip 11 of the cathode shaft 15, causing flicker in the light output. Further, the diameter of the cathode shaft 15 is 0.
In the case of 25 mm (S / I = 0.026), the tip 11 of the electrode shaft was consumed due to the high lamp current at the time of starting. Further, even in a lamp having a diameter of the cathode shaft 15 of 0.3 mm, the protrusion length L of the tip 11 of the electrode shaft from the coil 10 is L.
When 0.5 mm is 0.5 mm, there is a lamp that can be formed in the coil 10 where the arc spot is close to the tip 11, and it has been found that a protrusion length of at least twice the diameter of the electrode shaft 15 is desirable.

As a second embodiment, a 250 W input power lamp will be described. Inner diameter 10.5 mm, inner volume 1.0 c
tungsten anode 2 in a quartz arc tube 3 m ³ and the cathode 1
Were sealed at intervals of 3.0 mm. Cathode 1
Is a tungsten shaft 15 having a diameter of 0.4 mm and a coil 10 made of a tungsten wire having a diameter of 0.3 mm mounted so that the protruding length L of the tip 11 is 1.0 mm. , Without coil, up to 16 parts
Using a tungsten shaft with a diameter of 2.4 mm, the tip 1
The corner of the No. 2 was cut to have a diameter of 0.5 mm, and the quartz glass sealing portion 13 was ground to a diameter of 0.8 mm. Pellets 0.45 mg and indium iodide 0.8 mg in which dysprosium iodide, cadmium iodide and cesium iodide were mixed at a molecular ratio of 1: 1
Then, 44 mg of mercury and 150 Torr of argon gas were sealed at room temperature. The lamp had an initial voltage of 64 V, a lamp current of 3.91 A, an efficiency of 66 lumen / W, and a color temperature of 7200K. A lighting life test of 1500 hours was performed with three lamps of this specification with the discharge direction horizontal.
The discharge was stable, and only a slight white turbidity was observed on the upper wall of the quartz tube 3 without blackening, indicating a very good life characteristic (S / I = 0.032).

In the lamp of this specification, a tungsten shaft (S / I = 0.0) having a diameter of 0.5 mm is used as the cathode shaft 15.
Good results were also obtained when 502) was used. However, the lamp using a tungsten shaft having a diameter of 0.65 mm as the cathode shaft 15 (S / I = 0.0848) was defective because flicker occurred in 2 out of 4 lamps. Furthermore, the diameter is 0.
Lamp with 3 mm tungsten shaft (S / I = 0.
(0175), the wear of the tip 11 of the cathode shaft was remarkable even after 100 hours of lighting. Further, in a lamp in which the projection length L of the tip 11 of the cathode shaft 15 is 0.6 mm, the arc spot has a tip 1
There was a lamp in the coil 10 at a position close to 1, which was a problem.

[0012]

As described above, the present invention suppresses the occurrence of white turbidity, which is a major drawback of a lamp for a liquid crystal projection display using a rare earth halide as a light emitting substance, by a lighting posture in which the discharge direction is horizontal and direct current lighting. In the lamp, which is suitable for a light source for a liquid crystal projector, is intended to obtain a stable discharge without flicker, paying particular attention to the design of the cathode, the cathode shape of the present invention, the arc pot of the cathode shaft It is possible to obtain a lamp that is reliably formed at the tip and is capable of stable light emission without flickering.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating an embodiment of a lamp of the present invention.

FIG. 2 is an explanatory view of an embodiment of a cathode structure used in the lamp of the present invention.

[Explanation of symbols]

 1 Cathode 2 Anode 3 Quartz arc tube 4 Sealing part 5 Molybdenum foil 6 External lead rod 10 Coil 32 Insulating film

Claims (3)

[Claims] 1. A short arc metal halide lamp comprising a cathode and an anode larger than the cathode, at least containing a rare earth halide and mercury, and having a discharge direction substantially horizontal and being lit by DC power, the cathode being made of tungsten. When a tungsten coil is wound around the electrode shaft, the cross section of the electrode shaft of the cathode is S square millimeter, and the current during steady lighting is I ampere, S is I
A short arc metal halide lamp for direct current lighting, wherein the value divided by is larger than 0.029 and smaller than 0.076. 2. The short arc metal halide lamp for direct current lighting according to claim 1, wherein the tip of the electrode shaft of the cathode projects from the coil with a length that is at least twice the electrode shaft diameter of the cathode. . 3. The short arc metal halide lamp for direct current lighting according to claim 2, which is incorporated in a liquid crystal projection display device.