JPH10261384A - Metal halide lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal halide lamp with the best lamp characteristic which suppresses the drop of the lumen maintenance factor. SOLUTION: A lamp is formed by using an electrode the tip section of which is represented by S to be lit by satisfying an expression 70.0<=E.J<=150.0 [V.A/mm<2> ] (E: lamp electric field E=V/d [V/mm], and j: current density j=I/S [A/mm<2> ]), where the distance between the electrodes = d (mm), the section of the electrode tip = S (mm<2> ), the lamp voltage when stable lighting = V [V] and the lamp current = I [A]. Then a lamp voltage rise and color temperature variation are suppressed and the long life of the lamp is realized by suppressing the tube wall blackening in an initial stage of lighting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-pressure discharge lamp, and more particularly, to a metal halide lamp which satisfies predetermined conditions at the time of lighting.

[0002]

2. Description of the Related Art Conventionally, the design of a metal halide lamp is as follows.
Lamp power, which is a restriction from the lighting circuit design side to ensure the required light quantity, and especially when used as a light source for projectors, a request from the optical design side is to increase the brightness of the light-emitting arc part by increasing the distance between the electrodes. (Arc length) is limited. On the other hand, it is well known that electrode design is important in the design of metal halide lamps, and that the quality of the electrode design has a large effect on lamp characteristics (such as the luminous flux maintenance factor).

[0003] However, there is no firm guideline for designing an electrode with the best lamp characteristics (good luminous flux maintenance ratio) for design restrictions such as lamp power and distance between electrodes, and the empirical portion is still being worked on. There are many.

[0004]

As described above, the lamp characteristics become the best with respect to the design restrictions such as the lamp power and the distance between the electrodes (the luminous flux maintenance ratio is good, and the brightness of the discharge arc portion is high). ) It is necessary to find guidelines for electrode design.

According to the present invention, the product of the lamp electric field and the current density relating to the distance between the electrodes and the shape of the electrodes is defined as the luminous flux maintenance factor and the average temperature of the electrode tip, while the lamp power and the distance between the electrodes are limited in design. It is an object of the present invention to devise an electrode design technique that suppresses a decrease in the luminous flux maintenance rate by increasing the brightness of the discharge arc part by finding out that there is a correlation with the above, and to provide a lamp based thereon.

[0006]

To achieve the above object, the following means are used.

(1) Distance d [mm] between electrodes, cross-sectional area S [mm ² ] of electrode tip, lamp voltage V during stable lighting
[V] and the lamp current I [A], 70.0 ≦ E ·
j ≦ 150.0 [V · A / mm ³ ] (E: lamp electric field
E = V / d [V / mm], j: current density j = I / S
[A / mm ² ]), the lamp is constituted by using an electrode having a cross section of S at the tip of the electrode so that the lamp is lit when satisfying [A / mm ² ]).

(2) Electrode distance d [mm], electrode tip cross-sectional area S [mm ² ], electrode tip average temperature T [K], lamp voltage V [V] during stable lighting, lamp current I [ A], 70.0 ≦ E · j ≦ 150.0 [V · A / mm
³ ] (E: lamp electric field E = V / d [V / mm], j:
An electrode having a cross-sectional area of S at the tip of the electrode is used so as to emit light while satisfying current density j = I / S [A / mm ² ]), and is emitted while satisfying 2300 ≦ T ≦ 2700 [K]. A lamp is formed by using an electrode having a portion in which the cross-sectional area of each part of the electrode is different from the tip portion between the tip portion and the arc tube sealing portion.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a metal halide lamp according to the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 shows a metal halide lamp according to an embodiment of the present invention.
This is a state in which a discharge arc 3 is generated between the discharge electrodes 1 disposed opposite to each other in the arc tube 2 and stable lighting is performed.
A lamp voltage V is applied between the discharge electrodes 1, and a lamp current I flows. The distance between the electrodes is d. The cross-sectional area of the tip of the discharge electrode 1 supporting the discharge arc 3 is represented by S.
A mercury metal and at least one metal halide are sealed in the arc tube.

The distance d between the electrodes is 1.8 to 13 mm,
Electrode tip cross section S = 0.169-1.327 mm
² (Electrode tip is a circular flat surface, diameter φ = 0.5 ~ 1.3m
m), an arbitrary combination was used, and the state of the luminous flux maintenance ratio with respect to 0 hours after the start of lighting for 100 hours after the start of lighting was measured in various metal halide lamps having different enclosed metal halides and different lamp powers.

In FIG. 2, the horizontal axis represents the lamp electric field E (= lamp voltage V / interelectrode distance d [V / m) at 0 hours after the start of lighting.
m]) and the current density j (= lamp current I / electrode tip cross-sectional area S [A / mm ² ]), and the ordinate indicates the luminous flux maintenance factor.

The reason why the luminous flux maintenance factor at the start of lighting 100 hours is taken up is that the main cause of the decrease of the luminous flux maintenance at about 100 hours after lighting is blackening of the inner wall of the arc tube (the electrode material evaporates and scatters during lighting and emits light. This is because the light transmittance is attenuated by adhering to the inner wall of the tube, and the degree of progress of the blackening is related to the electrode shape.

FIG. 2 shows a classification based on three conditions based on the difference between the enclosed halogen metal and the lamp power. The circle (○) indicates indium-holmium, lamp power 200 W, and the diamond (◇) indicates indium-thulium, lamp power 200 W.
These two types are development prototypes, and the black diamonds (◆) are dysprosium-thallium-sodium-holmium-thulium with a lamp power of 150 W, which is a commercial product (Matsushita Electric). The distance d between the electrodes and the cross-sectional area S of the tip of the electrode were measured under the conditions arbitrarily combined within the range described above.

The unit of E · j on the horizontal axis is [VA · /
mm ³ ] or [W / mm / mm ² ], which is the energy density per unit length of the discharge arc received by the front surface of the electrode tip per unit area. From the results shown in FIG. 2, it can be seen that the luminous flux maintenance factor becomes worse as E · j increases.

This is because, when the energy density E · j increases, the energy transfer from the discharge arc to the discharge electrode increases particularly in front of the electrode tip, so that the temperature at the electrode tip rises and the electrode material evaporates. Alternatively, the electrode material is scattered due to the collision of the particles with a high energy density against the tip of the electrode, and the blackening of the arc tube wall progresses, thereby deteriorating the luminous flux maintenance factor. The central straight line is a regression line.

FIG. 3 is a graph showing the relationship between the value of E · j and the average temperature of the electrode tip at 0 hours from the start of lighting. The target lamp is the same as in FIG. From this figure, it is confirmed that the electrode tip temperature increases as E · j increases. The method for measuring the electrode tip average temperature will be described in Appendix.

FIG. 4 shows how the luminous flux maintenance ratio changes as the lighting time of a typical metal halide lamp increases. A is a lamp having a luminous flux maintenance rate of 80% for 100 hours after the start of lighting. In this case, about 5000 hours are obtained as the luminous flux half life. This number of 5000 hours is an average number for a metal halide lamp for general lighting in which the distance between the electrodes is generally 10 mm or more, and the distance between the electrodes incorporated in a projector or the like is 3 m.
This is the highest level for a metal halide lamp of about m.

Based on this, the lighting start 10 in FIG.
When the necessary luminous flux maintenance factor at time 0 is set to 80%, the value of E · j to be satisfied at that time is 150 V · A / m.
m ³ it can be seen that the less.

A metal halide lamp for general lighting (manufactured by Matsushita Electric Co., Ltd.) having a distance between the electrodes of generally 10 mm or longer (manufactured by Matsushita Electric Co., Ltd.) includes a lamp marked with a black diamond (◆) in FIG. Distance between electrodes 10-8
At 0 mm, the value of E · j is 69 to 12 [V · A / m
m ³ ], and a luminous flux maintenance ratio of 90% or more at 100 hours after the start of lighting is confirmed. In FIG. 2, it is plotted at the upper left.

However, such a metal halide lamp for general lighting, in which the distance between the electrodes is 10 mm or more, has a low luminance of the light emitting portion arc, and therefore cannot be used in a projection optical system when used as a light source for a projector. FIG. 5 shows the lamp luminous flux / electrode distance [lm / mm] as a value correlated with the luminance of the discharge arc portion, as a value on the horizontal axis E · j.

The aforementioned lamp power of 70 to 1000 W,
The distance between the electrodes is 10 to 80 mm, and the value of E · j is 69 to 12 [V
The value of the luminous flux / electrode distance of the lamp operating at [A / mm ³ ] is 420 to 1060 [lm / mm].
It is plotted in the lower left, including the middle and black diamonds (◆).
As the value of E · j decreases, the lamp luminous flux / electrode distance also decreases. The lamp luminous flux / electrode distance must be at least 4000 [lm / mm] in order to secure the required screen illuminance for a 40-inch class projector.
According to FIG. 5, the value of E · j to be satisfied at that time is 70 V · A
/ Mm ³ or more. The straight line in FIG. 5 is a regression line.

In FIG. 5, a circle (○) and a diamond (◇)
The reasons why the marked ramps fluctuate above and below the regression line are as follows. A series of lamps showing the characteristics of a steep slope and rising to the right above the regression line have the same electrode tip cross-sectional area S and are the results of a sample group with different interelectrode distances d. A series of lamps exhibiting the upward-sloping characteristics are the results of a sample group in which the distance d between the electrodes is the same and the sectional area S of the electrode tip is different.

In each case, the lamp luminous flux / interelectrode distance 4
To obtain 000 [lm / mm], the value of E · j is 70 V ·
A / mm ³ or more is required, so there is no change. However, it is interesting that the degree of the influence of the distance d between the electrodes and the sectional area S of the electrode tip on the lamp luminous flux / the distance between the electrodes is different.

From FIGS. 2 and 5, E.E. is effective for a lamp in which the luminous flux maintenance rate at 100 hours after the start of lighting satisfies 80% or more and the value of lamp luminous flux / interelectrode distance satisfies 4000 [lm / mm]. The value of j is 70.0 ≦ E · j ≦ 1
It can be said that it is 50.0 [V · A / mm ³ ]. In FIG. 6, it is a shaded portion.

As a result, 70.0 ≦ E · j ≦ 150.0
The lighting operation range of [VA · mm ³ ] does not overlap with the lighting operation range of existing metal halide lamps. This means that there has not been a lamp that satisfies the two requirements of a high luminous flux maintenance ratio and a high lamp luminous flux / electrode distance (≒ luminance of the light emitting arc portion) in addition to a good luminous flux maintenance ratio. . In recent years, light sources have been used as key components of display devices such as projectors, and light sources with high luminance and excellent luminous flux maintenance ratio will become increasingly important in the future.

(Second Embodiment of the Invention) As described in the first embodiment of the present invention, when the value of E · j is reduced in accordance with FIGS. Although the reduction is suppressed and the luminous flux half-life of the lamp is extended, there are cases where it is difficult to realize the lamp design. That is, the distance between the electrodes incorporated in the projector etc. is 3mm
The following (1.5 mm to 3 mm) metal halide lamp. The value of E · j is determined by the lamp power (= V × I), the distance d between the electrodes, and the cross-sectional area S of the electrode tip. However, the lamp power is limited by the lighting circuit design side in order to secure a necessary light amount. When the distance d between the electrodes as a request from the optical design side is limited, the design parameter is only the electrode tip section cross-sectional area S.

The value of E · j can be reduced by increasing S. However, the upper limit of the sectional area S of the electrode tip is also determined for the following reason. It is a viewpoint of the balance between the thickness of the discharge arc and the optical design. Generally, as the cross-sectional area S of the electrode tip supporting the discharge increases, the discharge arc between the electrodes also tends to increase. When a lamp is used by being incorporated into an optical system such as a condensing projection system, if the discharge arc becomes thicker, the brightness of the discharge arc decreases, and finally the amount of light that can be extracted from the optical system decreases. Therefore, a case may occur in which an electrode having a small tip cross-sectional area must be used to some extent.

There is a method of further improving the reduction of the luminous flux maintenance rate while keeping the electrode tip sectional area S fixed, that is, the value of E · j fixed. What is necessary is just to control the temperature of the electrode front-end | tip part.

FIG. 7 shows the luminous flux maintenance ratio at 100 hours from the start of lighting to the average temperature at the tip of the electrode at 0 hours from the start of lighting. The target lamp is the same as in FIGS. FIG. 7 shows that it is difficult to achieve the luminous flux maintenance ratio of 80% or more described in the first embodiment of the present invention if the average temperature at the electrode tip is 3000 K or more. In particular, in order to realize a luminous flux maintenance rate of 85% or more, the average temperature at the electrode tip is 2300 to 270 from this figure.
It can be seen that 0K is sufficient. This figure of 85% is illustrated in FIG. By realizing a luminous flux maintenance rate of 85% or more at 100 hours from the start of lighting, the luminous flux half-life is further increased by 2000 as compared with A as shown in FIG.
7000 hours, which is nearly an hour, will be realized.

That is, there is a difference in the average temperature at the tip of the electrode even at the same value of E · j in FIG. 3, and this results in a difference in the luminous flux maintenance factor despite the same value of E · j in FIG. Responsible. FIG. 8 shows the range of the electrode tip average temperature with respect to the value of E · j appealed in this section. This is a shaded portion in FIG. The metal halide lamp operating within this range has a luminous flux maintenance ratio of 85 at 100 hours from the start of lighting.
% Or more, and a luminous flux half-life of 7000 hours can be obtained.

In order to suppress the reduction of the luminous flux maintenance rate while keeping the value of E · j fixed, that is, the lamp power (= V × I), the distance d between the electrodes, and the sectional area S at the electrode tip, the average of the electrode tip is reduced. As a method for setting the temperature to a required value, a method is used in which a cross-sectional area of each part of the discharge electrode is different from the tip part between the tip part and the arc tube sealing part. FIG. 9 shows an example. The electrode coil 6 is welded to a columnar intermediate portion serving as the electrode shaft 5.

In this manner, there is a portion having a sectional area of S _B between the electrode tip section S _A and the arc tube sealing section 4 (FIG. 1) with respect to S _A. In FIG. 9, the length from the electrode tip to the electrode coil 6 is called a protruding length. FIG. 10 shows E in which the lamp power, the interelectrode distance d, and the cross-sectional area S of the electrode tip are equal.
In the lamp in which the value of j is in the range of 100 to 120 V · A / mm ³ , it is a state of the average temperature of the electrode tip portion with respect to the protruding length.

In this case, it is confirmed that the average temperature at the tip end of the electrode is reduced by reducing the protrusion length. That is, by providing a portion having a cross-sectional area different from that of the tip portion from the electrode tip portion to the arc tube sealing portion, and appropriately selecting the position, the electrode tip portion average temperature can be maintained while the value of E · j is fixed. The required value can be set, and the decrease in the luminous flux maintenance ratio can be suppressed.

The sectional area S of the tip of the electrode supporting the discharge
[Mm ² ] may be formed including a curved surface. This situation will be described with reference to FIG. 11 in which the electrode tip is spherical. In this case, the sectional area S of the electrode tip is the vertical sectional area 8 with respect to the discharge arc axis 7 of the portion where the electrode tip supports the discharge arc. When the portion supporting the discharge includes a curved surface, the cross-sectional area 8 of the portion in the vertical direction with respect to the arc axis is the minimum area supporting the discharge. At this time, the value of E · j as the calculated value becomes the largest, and the luminous flux maintenance ratio is the most disadvantageous condition as compared with FIG.

If a curved surface is included, the actual surface area 9 becomes larger than at least the vertical cross-sectional area 8 and changes in the direction in which the luminous flux maintenance rate is improved. For the above reasons, the cross-sectional area in the vertical direction with respect to the discharge arc axis is used.

In order to provide a portion where the sectional area of each part of the discharge electrode is different from the tip portion from the tip portion to the arc tube sealing portion, in addition to the method using the electrode coil 6 as shown in FIG. An electrode made of a single material as shown in FIG. 12 and having all the concavities and convexities in the sectional area of each part may be formed by integral cutting.

(Supplementary Note) Method for Measuring Average Temperature of Electrode Tip Part This measuring method is described in Japanese Patent Application Laid-Open No. Hei 8-152360 (Japanese Patent Application No. 6-295247), "Radiation Temperature Measuring Apparatus" and "Metal halide lamp by Kai and Takeda. In the method described in "Electrode Temperature Measurement Study" (1996 Annual Meeting of the Illuminating Engineering Institute of Japan), the two-color radiation temperature is obtained in which the spectral radiance ratio of any two different monochromatic wavelengths emitted from an object is a function of the temperature of the object. It is based on the principle of the measuring method.

However, since the lit electrode is buried in the sheath of the arc discharge, radiation from the arc discharge is mixed when detecting thermal radiation, and the conventional method such as pyrometer can correctly detect radiance. It was difficult. Therefore, in order to detect the heat radiation from the electrode without mixing it with the radiation from the arc discharge, the spectral distribution in the vicinity of the electrode is measured using a high-resolution spectrometer (resolution 0.01 nm). The inventors found a narrow band monochromatic dual wavelength with very little radiation, measured the thermal radiation luminance from the electrodes at these two wavelengths, and determined the temperature from the luminance ratio.

The average temperature at the tip of the electrode used in the embodiment of the present invention is measured by using a two-dimensional photodetector (CCD camera) as a means for detecting the thermal radiance from the electrode based on the method described above. , The average temperature at the tip.

[0041]

Empirically, it has been pointed out that the blackening of the arc tube wall is associated with not only a decrease in luminous flux but also a factor that deteriorates lamp characteristics such as an increase in lamp voltage and a change in color temperature during operation. . According to the present invention, if blackening of the tube wall at the beginning of lighting is suppressed, it is possible to suppress an increase in lamp voltage and a change in color temperature, thereby realizing a longer lamp life.

Further, the present invention can be widely applied to lamps having different enclosed halogen metals and lamp powers, and the degree of freedom of design and development efficiency can be significantly increased.

In recent years, a light source has been used as a main component of a display device such as a projector, and the added value of the light source having a high luminance and an excellent luminous flux maintenance ratio according to the present invention is added. Greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a metal halide lamp according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between E · j used in the present invention and a luminous flux maintenance ratio (lighting start time of 100 hours).

FIG. 3 is a graph showing the relationship between E · j used in the present invention and the average temperature of the electrode tip.

FIG. 4 is a graph showing a relationship between a lighting time and a luminous flux maintenance factor used in the present invention.

FIG. 5 is a graph showing the relationship between E · j and lamp luminous flux / distance between electrodes used in the present invention.

FIG. 6 is a graph showing the relationship between E · j used in the present invention, the luminous flux maintenance ratio (100 hours from the start of lighting), and the luminous flux / distance between electrodes.

FIG. 7 is a graph showing a relationship between an average temperature of an electrode portion used in the present invention and a luminous flux maintenance factor.

FIG. 8 is a graph showing the relationship between E · j used in the present invention and the average temperature of the electrode tip.

FIG. 9 is a structural view of a discharge electrode for a metal halide lamp according to a second embodiment of the present invention.

FIG. 10 is a graph showing the relationship between the protrusion length used in the present invention and the average temperature of the electrode tip.

FIG. 11 is a structural diagram of a discharge electrode for a metal halide lamp according to a second embodiment of the present invention.

FIG. 12 is a structural diagram of a discharge electrode for a metal halide lamp according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge electrode 2 Arc tube 3 Discharge arc 4 Arc tube sealing part 5 Electrode axis 6 Electrode coil 7 Discharge arc axis 8 Vertical cross-sectional area 9 Surface area

Claims (5)

[Claims] 1. A metal halide lamp having a pair of discharge electrodes inside an arc tube and in which mercury and at least one or more metal halides are enclosed, wherein a distance d [m
m], electrode tip cross-sectional area S [mm ² ], lamp voltage V [V] during stable lighting, lamp current I [A], when lighting, 70.0 ≦ E · j ≦ 150.0 [V A / mm ³ ] (E: lamp electric field E = V / d [V / mm], j: current density j = I / S [A / mm ² ]). 2. A metal halide lamp which has a pair of discharge electrodes inside an arc tube and in which mercury and at least one or more metal halides are sealed, wherein a distance between the electrodes is d [m
m], electrode tip cross-sectional area S [mm ² ], electrode tip average temperature T [K], lamp voltage V [V] during stable lighting, lamp current I [A], when lighting, 70.0 ≦ E · j ≦ 150.0 [VA / mm ³ ] (E: lamp electric field E = V / d [V / mm] j: current density j = I / S [A / mm ² ]) And a metal halide lamp satisfying 2300 ≦ T ≦ 2700 [K]. 3. The metal halide lamp according to claim 2, wherein the cross-sectional area of each part of the discharge electrode has a portion different from the tip portion between the tip portion and the arc tube sealing portion. 4. A sectional area S [mm
The metal halide lamp according to claim ^{2, wherein} [ ² ] is formed including a curved surface. 5. The metal halide lamp according to claim 3, wherein the discharge electrode is made of a single material, and all the irregularities in the sectional area of each part are formed by integral cutting.