Short arc type mercury lamp

Abstract

To provide a long-life short arc type mercury lamp.SOLUTION: A short arc type mercury lamp includes a cathode 4, an anode 3, an arc tube 1, and a side tube, and satisfies the following formula (1) in a cross section passing through the axis of rotational symmetry. (In formula (1), A1 (mm): represents the length in the uniaxial direction from the closest position where the arc tube is closest to the anode to the anode side end of the arc tube, B1 (mm): represents the inner diameter of the arc tube at the closest position, C1 (mm): represents the length in the rotational symmetry axis direction from the anode side end of the arc tube to the cathode side end, and D1 (mm): represents the inner diameter of the arc tube at the most bulging position of the arc tube.)SELECTED DRAWING: Figure 4B

Description

[Technical field]

[0001] The present invention relates to a short arc type mercury lamp. [Background technology]

[0002] Short arc type mercury lamps have been known as light sources used in exposure devices for manufacturing semiconductors, display devices, wiring boards, etc. In a short arc type mercury lamp, an anode and a cathode for discharge are arranged opposite each other in an arc tube that emits light by discharge, and mercury is sealed in as a light emitting gas. The anode and the cathode are each supported by a lead rod, and each lead rod is supported by a pair of side tubes connected to both ends of the arc tube. Patent Document 1 shows an example of such a short arc type mercury lamp. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-128755 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a short arc type mercury lamp is turned on and an arc discharge occurs between the electrodes, some of the material that makes up the electrodes detaches from the electrodes. The material that detaches from the electrodes then diffuses with the flow of gas, such as light-emitting gas, enclosed in the arc tube 1 (hereinafter, all gases enclosed in the arc tube 1 will be simply referred to as "gas") and may adhere to the inner surface of the glass tube that makes up the arc tube 1, gradually forming a blackened area. When a blackened area forms on the inner surface of the glass tube, the transmittance of the glass tube decreases, and the illuminance of the light emitted from the lamp decreases. This indicates that the lamp's service life will be shortened.

[0005] On the other hand, there is a market demand for longer life short arc type mercury lamps. In order to meet the market demand, it is an object of the present invention to provide a long life short arc type mercury lamp. [Means for solving the problem]

[0006] The details will be described later, but the inventors have noticed that when the blackened area is formed outside the effective light utilization angle, the illuminance does not decrease and the service life does not deteriorate, and have investigated the gas flow to form the blackened area as far as possible outside the effective light utilization angle. As a result of the inventors' intensive research, they have found the characteristics of the lamp that realize this gas flow.

[0007] The short arc type mercury lamp of the present invention has the following features: A cathode; an anode disposed opposite the cathode on one axis and having a larger volume than the cathode; an arc tube having the cathode and the anode therein, mercury sealed therein, and exhibiting a rotationally symmetric shape about the axis; a first side tube formed at an anode side end portion close to the anode and a second side tube formed at a cathode side end portion close to the cathode, In a cross section passing through the axis, the following formula (1) is satisfied.

number

[0008] Although details will be described later, in the above-mentioned short arc type mercury lamp, the volume of the upper space inside the light emitting tube is secured, so the gas flow above the anode is unlikely to become turbulent. If turbulence occurs above the anode, the gas flow will head toward the inside of the effective light utilization angle of the light emitting tube, but by suppressing the turbulence above the anode, the gas flow can be directed outside the effective light utilization angle of the light emitting tube.

[0009] Furthermore, the following formula (2) may be satisfied.

number

[0010] This makes it possible to provide a long-life short-arc type mercury lamp. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an embodiment of a short arc type mercury lamp. [Figure 2A] FIG. 2 is an enlarged view of a main part of FIG. 1, showing a gas flow. [Figure 2B] FIG. 2 is an enlarged view of a main part of FIG. 1, showing a gas flow. [Diagram 3] FIG. [Figure 4A] FIG. 1 shows the anode only. [Figure 4B] FIG. 2 is a diagram mainly showing an arc tube and an anode. [Figure 5A]13 is a graph showing the relationship between an approximate value P1 of the volume ratio and an elevation angle θ1. [Figure 5B] 1 is a graph showing the relationship between a parameter P2 and an elevation angle θ1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The above-mentioned short arc type mercury lamp will be described with reference to the drawings. Note that the drawings disclosed in this specification are merely schematic illustrations. In other words, the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0013] In the following, the XYZ coordinate system will be referred to as appropriate. In addition, in this specification, when expressing a direction, if a positive or negative direction is to be distinguished, it is described with a positive or negative sign, such as "+X direction" and "-X direction". In addition, when a direction is to be expressed without distinguishing between positive and negative directions, it is simply described as "X direction". In other words, in this specification, when simply described as "X direction", both "+X direction" and "-X direction" are included. The same applies to the Y direction and the Z direction. The -Z direction represents the vertical downward direction (the direction of gravity).

[0014] [Overall structure of the lamp] FIG. 1 shows an embodiment of a short arc type mercury lamp. A short arc type mercury lamp 100 (hereinafter referred to as "lamp 100") of this embodiment has an arc tube 1, an anode 3 and a cathode 4 arranged inside the arc tube 1 and spaced apart in the Z direction to face each other, a first side tube 2a connected to one end of the arc tube 1 in the tube axis direction (Z direction), a second side tube 2b connected to the other end of the arc tube 1 in the tube axis direction, a first lead rod 5a connected to the anode 3, and a second lead rod 5b connected to the cathode 4. Mercury is sealed inside the arc tube 1. When a voltage is applied between the cathode 4 and the anode 3, an arc discharge occurs in the mercury vapor and the lamp 100 emits light. In this specification, a "short arc type" lamp is a discharge lamp in which the anode 3 and the cathode 4 are arranged to face each other with a gap of 35 mm or less (value at room temperature without thermal expansion). The discharge lamp may be a short arc type in which the anode 3 and the cathode 4 are arranged facing each other with a gap of 20 mm or less. The details of the anode 3 and the cathode 4 will be described later.

[0015] When the lamp 100 is used, the lamp 100 is supported vertically so that the tube axis direction of the arc tube 1 is along the Z direction. The reasons for this are that (1) the gas in the arc tube 1 is likely to convect evenly around the tube axis direction, resulting in excellent luminous efficiency, and (2) the lead rod (particularly the first lead rod 5a) is likely to withstand the weight of the electrodes (particularly the anode 3), and the lead rod is unlikely to bend or break. Furthermore, the lamp 100 is preferably arranged so that the anode 3 is located above (on the +Z direction side of) the cathode 4. When the lamp 100 is turned on, if the gas in the arc tube 1 is heated, it convects to the upper part of the arc tube 1, so that the upper part of the arc tube 1 becomes hotter than the lower part of the arc tube 1. Since the anode 3 is larger than the cathode 4, the anode 3 has a higher heat resistance than the cathode 4. Therefore, by arranging the lamp 100 so that the anode 3 is located above the cathode 4, the heat resistance of the entire lamp 100 can be improved. The anode 3 and the cathode 4 are made of a material containing a high melting point metal, such as tungsten.

[0016] The arc tube 1 sandwiched between the first side tube 2a and the second side tube 2b is a region whose inner diameter expands from the end in the -Z direction or the +Z direction toward the center of the arc tube 1. The arc tube 1 is an arc tube that has a rotationally symmetric shape centered on the Z1 axis. For example, it may be a sphere centered on a point on the Z1 axis, or an ellipsoid with the Z1 axis as the axis of rotation. In this specification, whether or not the shape is rotationally symmetric, spherical, or ellipsoid is not strictly determined based on the measurement results of the shape and dimensions, but is determined from the rough overall shape. Specifically, even if the dimensions of the shape deviate from the rotationally symmetric shape, sphere, or ellipsoid due to manufacturing errors or local distortion, or if a protrusion called a tip tube exists on the arc tube 1, if the overall shape of the arc tube 1 is roughly rotationally symmetric, spherical, or ellipsoid, it is determined to be rotationally symmetric, spherical, or ellipsoid.

[0017] The first side tube 2a and the second side tube 2b may each be centered on the Z1 axis. The first side tube 2a is connected to one end of the arc tube 1, and the second side tube 2b is connected to the other end of the arc tube 1. The insides of the first side tube 2a, the arc tube 1, and the second side tube 2b are in communication with each other. The insides of the first side tube 2a and the second side tube 2b are sealed from the outside of the lamp 100. The arc tube 1, the first side tube 2a, the second side tube 2b, the anode 3, and the cathode 4 may each have a rotationally symmetric shape centered on the common Z1 axis. Whether or not these parts have a rotationally symmetric shape is not strictly determined based on the measurement results of the shape and dimensions, but is determined from the rough overall shape. Specifically, even if the above parts deviate from the rotationally symmetric shape due to manufacturing errors or local distortion, they are determined to have a rotationally symmetric shape if they are roughly rotationally symmetric. However, the arc tube 1, the first side tube 2a, the second side tube 2b, the anode 3, and the cathode 4 do not have to have a solid of revolution shape. Also, the central axis of the arc tube 1, the central axis of the first side tube 2a, and the central axis of the second side tube 2b all overlap the Z1 axis, but the central axis of the arc tube 1, the central axis of the first side tube 2a, and the central axis of the second side tube 2b do not necessarily have to overlap a common axis. In Fig. 1, point RP is a reference point of the arc tube 1. The reference point RP is on the Z1 axis and is located equidistant from the tip of the anode 3 and the tip of the cathode 4.

[0018] The first lead rod 5a is connected to the anode 3 and extends in the Z direction within the first side tube 2a. The second lead rod 5b is connected to the cathode 4 and extends in the Z direction within the second side tube 2b. The central axes of the first lead rod 5a and the second lead rod 5b may overlap with the Z1 axis. The first lead rod 5a and the second lead rod 5b are made of a material containing a high melting point metal, such as tungsten.

[0019] The base 12a covers the side (-Z direction side) of the first side tube 2a distal to the reference point RP. The base 12b covers the side (+Z direction side) of the second side tube 2b distal to the reference point RP. The base 12a is electrically connected to the first lead rod 5a, and the base 12b is electrically connected to the second lead rod 5b. The lamp 100 is turned on by receiving power from an external power source (not shown) via the bases (12a, 12b).

[0020] [Effective angle and darkening area] Fig. 2A is an enlarged view of a main part of Fig. 1. Fig. 2B is a reference view showing the same part as Fig. 2A. The effective light utilization angle and desirable blackened area will be described with reference to Figures 2A and 2B. Figure 2A shows that a part of the surface of the arc tube 1 is in area A1. This area A1 represents the effective light utilization angle. The effective utilization angle A1 is the range in which the light emitted from the arc AR can be effectively extracted from the arc tube 1. In areas on the surface of the arc tube 1 outside the effective utilization angle A1, the light emitted from the arc AR is blocked by the electrodes (3, 4), and therefore the light emitted from the arc AR cannot be effectively extracted.

[0021] In FIG. 2A, a blackened area Ba1 is shown on the inner surface of the arc tube 1. The blackened area refers to a region of the glass tube where a substance that has detached from the electrodes (3, 4) has diffused with the gas flow and adhered to the inner surface of the glass tube that constitutes the arc tube 1, or a region of the glass tube where a substance that has detached from the electrodes (3, 4) has adhered. The arc tube 1 is usually colorless and transparent, whereas when a substance that has detached from the electrodes (3, 4) adheres to the arc tube 1, the arc tube 1 changes color to a dusky color and becomes opaque, and thus is called a blackened area. Note that in FIG. 2A, only the substance that has detached from the electrodes (3, 4) and adhered and accumulated on the inner surface of the arc tube 1 (the area hatched with diagonal lines) is shown as the blackened area Ba1. The longer the lamp 100 is used, the larger the area of ​​the blackened area Ba becomes and the lower the light transmittance becomes. This is one of the factors that shorten the service life of the lamp 100.

[0022] [Fluid Simulation] In the course of researching ways to extend the life of the lamp 100, the inventor realized that it was sufficient to maintain the transmittance within the effective utilization angle A1, and it was not necessary to maintain the transmittance outside the effective utilization angle A1. The inventor then carried out fluid simulations and repeated studies on a method for forming a blackened region outside the effective utilization angle A1, rather than suppressing the formation of the blackened region. The details will be described below.

[0023] FIG. 2A shows an example of gas flow obtained by a fluid simulation of the lamp 100. The dashed arrows f1 and f2a in this figure indicate the gas flow in the arc tube 1. When the temperature of the luminous gas near the arc rises, a gas flow f1 is formed that rises from the vicinity of the arc along the anode 3. The flow f1 then forms a flow f2a that rises along the anode 3. Since the gas flows f1 and f2a contain substances that have been detached from the electrodes (3, 4), particularly the anode 3, when the flow f2a collides with the arc tube 1 or the first side tube 2a, the substances that have been detached from the electrodes (3, 4) adhere to the collision area of ​​the arc tube 1 or the first side tube 2a, forming a blackened area Ba1. As shown in this figure, the blackened area Ba1 is mainly outside the effective utilization angle A1, so even if the blackened area Ba1 is formed, its effect on the intensity of the light extracted from the lamp 100 is small.

[0024] FIG. 2B shows gas flows obtained by a fluid simulation of a lamp different from the lamp 100. The gas flow f1 shown in FIG. 2B is almost the same as the gas flow f1 shown in FIG. 2A. However, the gas flow f2b following the gas flow f1 in FIG. 2B is different from the gas flow f2a in FIG. 2A. The flow f2b moves from the vicinity of the arc upward along the anode 3, proceeds radially outward of the arc tube 1, and collides with the arc tube 1. When the flow f2b collides with the arc tube 1, the material detached from the electrodes (3, 4) adheres to the collision area of ​​the arc tube 1. The blackened area B2 where the material detached from the electrodes (3, 4) adheres to the collision area of ​​the arc tube 1 is within the effective utilization angle A1. Therefore, when the blackened area Ba2 is formed, it has a large effect on the intensity of the light extracted from the lamp 100.

[0025] [Gas flow evaluation method] In this way, the difference in the direction of the gas flow f2 (f2a, f2b) following the gas flow f1 as seen in Figures 2A and 2B determines whether the blackened region is outside the effective utilization angle A1. Here, a method for evaluating the direction of the gas flow f2 will be described.

[0026] FIG. 3 is a perspective view of the vicinity of the anode 3 and the cathode 4. The points (m1 to m4) in FIG. 3 are monitoring points. The monitoring points are points for determining the direction of the gas flow f2 that affects whether the blackened region is outside the effective utilization angle A1. In other words, the direction of the gas flow f2 at the monitoring points determines whether the blackened region is outside the effective utilization angle A1.

[0027] The monitoring points (m1 to m4) can be expressed in an XYZ coordinate system with the reference point RP as the origin (X, Y, Z) = (0, 0, 0). In this embodiment, while continuing the fluid simulation, it was found that it is effective to set the monitoring points (m1 to m4) as follows. Monitoring point m1 (X,Y,Z)=(+30mm,0mm,+10mm) Monitoring point m2 (X,Y,Z)=(0mm,+30mm,+10mm) Monitoring point m3 (X,Y,Z)=(-30mm,0mm,+10mm) Monitoring point m4 (X,Y,Z)=(0mm,-30mm,+10mm) When the anode tip surface is used as a reference, all of the monitoring points (m1 to m4) are located 14.3 mm away from the anode tip surface in the +Z direction.

[0028] As shown in FIG. 3, the angle θ1 formed between the direction of travel of gas flow f2 at monitoring point m1 and the XY plane is the elevation angle component of flow f2. The magnitude of the elevation angle θ1 affects the position of the blackened region. The same is true for monitoring points m2 to m4, and the magnitude of the elevation angle θ at each of monitoring points m2 to m4 has a large effect on the position of the blackened region. And, as a result of the fluid simulation, it was found that when the elevation angle θ1 is 50 degrees (deg.) or more, the blackened region is likely to be obtained outside the effective utilization angle A1.

[0029] [Ramp parameters and elevation angles] Incidentally, the gas flow that affects whether or not the blackened region is outside the effective utilization angle A1 varies depending on parameters of the lamp 100, such as the size of the anode 3, the size of the arc tube 1, and the positional relationship of the anode 3 with respect to the arc tube 1. Therefore, a fluid simulation is used to obtain the relationship between the elevation angle θ1 of the flow f2 and the parameters of the lamp 100, which affect the gas flow that determines whether or not the blackened region is outside the effective utilization angle A1.

[0030] Table 1 shows the results of simulating the average elevation angle θ1 of the gas flow f2 for 12 lamps (numbered S1 to S12) with different parameters of the lamp 100.

[0031] [Table 1]

[0032] The parameters of lamp 100 in Table 1 will be described with reference to Figures 3, 4A, and 4B. Figure 4A is a diagram showing only the anode 3, and Figure 4B is a diagram showing mainly the arc tube 1 and the anode 3. Note that, unless otherwise specified, the various dimensions shown below are the maximum values ​​among multiple measured values ​​obtained by repeatedly measuring the dimensions of a component (anode 3, arc tube 1, or cathode 4) while rotating the component once around its central axis (e.g., Z1 axis). Anode diameter F2 (mm): represents the diameter of the anode 3 centered on the Z1 axis (see FIG. 4A). Anode total length L2 (mm): the length of the anode 3 in the Z direction (see FIG. 4A). Average of elevation angle θ1 (deg.): The arithmetic mean of the elevation angle θ1 (deg.) at each of the four monitoring points (m1 to m4) (see Figures 3 and 4A). Anode body length L1 (mm): the length in the Z direction of the body of anode 3 (the portion whose diameter is constant in the Z direction) (see FIG. 4A). Minimum distance J1 (mm): This represents the shortest distance from the closest position J2, where the arc tube 1 is closest to the anode 3, to the anode 3 (see FIG. 4B). More specifically, the minimum value of the measured values ​​obtained by measuring the distance between the arc tube 1 and the anode 3 while rotating the lamp 100 once around the Z1 axis is taken as the minimum distance J1. The closest position J2 is the position where this minimum value is measured (hereinafter, the definition of the closest position J2 is the same). Upper space length A1 (mm): The length in the Z-axis direction from point J2, where the arc tube 1 is closest to the anode 3, to the end of the inner surface of the arc tube 1 on the anode side (see FIG. 4B). Arc tube inner diameter B1 (mm): This is the inner diameter of the arc tube 1 at the closest position J2 where the arc tube 1 is closest to the anode 3 (see FIG. 4B). Total length C1 (mm) of arc tube: the length in the Z-axis direction from the anode side end of the inner surface of arc tube 1 to the cathode side end of the inner surface of arc tube 1 (see FIG. 4B). Maximum inner diameter D1 (mm) of arc tube: the inner diameter of arc tube 1 at the most bulging position of arc tube 1 (see FIG. 4B).

[0033] In this specification, there are expressions such as "an anode side end on the inner surface of the arc tube 1" and "a cathode side end on the inner surface of the arc tube 1". In reality, the positions of the ends of the "anode side end on the inner surface of the arc tube 1" and the "cathode side end on the inner surface of the arc tube 1" may not be clearly specified, for example, when they are R-shaped. In such cases, the boundary between an imaginary surface extending toward the first side tube 2a while maintaining the curvature of the inner surface of the arc tube 1, and an imaginary surface extending from the inner surface of the first side tube 2a toward the arc tube 1, is defined as the "anode side end on the inner surface of the arc tube 1", and the boundary between an imaginary surface extending toward the second side tube 2b while maintaining the curvature of the inner surface of the arc tube 1, and an imaginary surface extending from the inner surface of the second side tube 2b toward the arc tube 1, is defined as the "cathode side end on the inner surface of the arc tube 1".

[0034] In obtaining Table 1, the following parameters are set to the following common values: Taper angle θ2 of the anode (see FIG. 4A. In this figure, the apex angle, which is the same value as the taper angle of the anode 3, is given the symbol θ2): 100 (deg.) Anode tip diameter F3 (see Figure 4A): 8.0 (mm) Cathode tip taper angle: 60 to 90 (deg.) Note that since the tip taper portion of the cathode 4 is not fixed to a constant value, the tip taper angle is shown as a range. Cathode tip diameter: 4.5 (mm)

[0035] From Table 1, no correlation can be found between the individual values ​​of the various parameters of the anode 3 or the arc tube 1 and the elevation angle θ1 of the gas flow f2. However, the present inventor discovered from a fluid simulation image of the lamp 100 that the behavior of the gas flow f2 is related to the gas flow in the upper space U1 of the arc tube 1 (see FIG. 2B). That is, when the gas flow in the upper space U1 of the arc tube 1 becomes turbulent, it advances toward the radial outside of the arc tube 1 like gas flow f2b as shown in FIG. 2B (the elevation angle θ1 becomes smaller). When the gas flow in the upper space U1 of the arc tube 1 does not become turbulent, it rises along the anode 3 like gas flow f2a as shown in FIG. 2A (the elevation angle θ1 becomes larger). From this, the present inventor discovered that when the volume of the upper space U1 of the arc tube 1 is large compared to the volume of the entire space of the arc tube 1, the gas flow in the upper space U1 becomes turbulent.

[0036] Therefore, the correlation between the elevation angle θ1 and the ratio of the volume of the upper space U1 of the arc tube 1 to the volume of the entire space of the arc tube 1 is examined. However, since calculating the volume requires complex calculations, it takes time to calculate the ratio of the volume of the upper space U1 of the arc tube 1 to the volume of the entire space of the arc tube 1. Therefore, the product of the upper space length A1 and the arc tube inner diameter B1 is used as an approximation of the volume of the upper space U1 of the arc tube 1, and the product of the total length C1 of the arc tube and the maximum inner diameter D1 of the arc tube is used as an approximation of the volume of the entire space of the arc tube 1.

[0037] An approximate value P1 that approximates the ratio of the volume of the upper space U1 of the arc tube 1 to the volume of the entire space of the arc tube 1 is obtained by the following formula (3).

number

[0038] Table 2 shows the relationship between the elevation angle θ1 and the approximate value P1 (=[(A1·B1) / (C1·D1)]·100) of the volume ratio obtained by fluid simulation. [Table 2]

[0039] FIG. 5A is a graph showing Table 2 as a scatter plot with the volume ratio approximation P1 (=[(A1·B1) / (C1·D1)]·100) on the horizontal axis and the elevation angle θ1 on the vertical axis. The straight line T1 is an approximation line of the plot obtained by the least squares method. It can be seen that the value of the approximation P1 is correlated with the elevation angle θ1. As mentioned above, when the elevation angle θ1 is 50 degrees (deg.) or more, the blackened area is likely to be obtained outside the effective utilization angle A1, so it is preferable that the approximation P1 be 20 or less.

[0040] [experiment] The following experiment was carried out to confirm whether the above-mentioned fluid simulation results were appropriate. First, one lamp each having the dimensions of numbers S1 to S12 (see Table 1) used in the fluid simulation was manufactured, and 12 lamps with sample numbers S1 to S12 were obtained. The lamp sample numbers S1 to S12 correspond to the numbers S1 to S12 used in the fluid simulation in Table 1. Next, the 12 lamps were actually turned on for a predetermined time, and the 12 lamps were analyzed after that. Table 3 shows the analysis results of the 12 lamps. Whether or not the manufactured lamp 100 satisfies the parameters such as the minimum interval J1, the upper space length A1, the inner diameter B1 of the arc tube, the total length C1 of the arc tube, and the maximum inner diameter D1 of the arc tube, which are described in Table 1, can be obtained by projecting light (visible light, or X-rays in some cases) onto the lamp 100 and measuring the dimensions of the projected image. Table 3 also lists the average elevation angle θ1 obtained by the fluid simulation.

[0041] [Table 3]

[0042] The evaluation method of "degree of blackening" in Table 3 will be explained. The degree of blackening of the arc tube 1 can be evaluated by determining the illuminance maintenance rate of the lamp. The illuminance maintenance rate is a percentage of the illuminance of a light of a specified wavelength after the lamp is turned on for an arbitrary time, based on the initial illuminance immediately after the lamp is turned on after manufacture. In this experiment, the initial illuminance of the lamp immediately after the lamp is turned on after manufacture and the illuminance after the lamp is turned on for 2000 hours at the rated power were measured for sample numbers S1 to S12 using a photodetector sensitive to a wavelength of 365 nm. The measured illuminance after the lamp is turned on for 2000 hours at the rated power were divided by the measured initial illuminance and multiplied by 100 to obtain the illuminance maintenance rate (%). An illuminance maintenance rate of 90% or more was evaluated as AA, 85% or more but less than 90% was evaluated as A, and less than 85% was evaluated as B. Here, the evaluation values ​​are indicated in order of AA, A, and B, indicating better results. Specifically, when the illuminance maintenance rate is rated AA, it is considered that the degree of blackening is very little and it is excellent, when the illuminance maintenance rate is rated A, it is considered that the degree of blackening is little and it is a good product (the lamp life has not been reached), and when the illuminance maintenance rate is rated B, it is considered that the degree of blackening is large and it is a poor product (the lamp life has been reached). From Table 3, it was found that when the elevation angle θ1 is 50.0 degrees or more, an evaluation of AA or A was obtained. It was confirmed that this result is consistent with the fluid simulation results. It was also found that when the elevation angle θ1 is 53.0 degrees or more, an evaluation of AA was obtained.

[0043] Regarding the evaluation method for "presence or absence of distortion" in Table 3, we will first explain the significance of evaluating "distortion." For lamps with sample numbers S1 to S12, the amount of heat received by the material (e.g., quartz glass) that constitutes the arc tube 1 varies due to differences in various lamp parameters. If the amount of heat exceeds the heat resistance of the material that constitutes the arc tube 1, distortion will occur in that material, shortening the lamp's lifespan. Therefore, the lamps that have been lit for 2000 hours at rated power are evaluated for "presence or absence of distortion."

[0044] The method for evaluating the "presence or absence of distortion" will now be described. It is generally known that when distortion occurs in the material (e.g., quartz glass) that constitutes the light-emitting tube 1, it exhibits the property of birefringence. Therefore, the amount of distortion is measured using the crossed Nicol method, which is one of the photoelasticity experimental methods that utilizes this property. That is, when a sample is inserted between a polarizer and an analyzer that are arranged perpendicular to each other and monochromatic light is transmitted through it, the distorted parts appear bright and white, and the non-distorted parts appear dark and black. When the analyzer is rotated until the transmitted light in the distorted parts becomes dark, this rotation angle is expressed as the magnitude of distortion.

[0045] In this experiment, the analyzer was rotated until the transmitted light in the distorted portion became dark. When the rotation angle was less than 20 degrees, it was evaluated as AA, when it was 20 degrees or more but less than 45 degrees, it was evaluated as A, and when it was 45 degrees or more, it was evaluated as B. Here, the evaluation values ​​are AA, A, and B in order of better results. Specifically, when the presence or absence of distortion is evaluated as AA, it is considered that the lamp is not affected by the distortion of the arc tube 1 and is extremely excellent, when the presence or absence of distortion is evaluated as A, it is considered that the lamp is not affected by the distortion of the arc tube 1 and is a good product, and when the presence or absence of distortion is evaluated as B, it is considered that the lamp is not affected by the distortion of the arc tube 1 and is a defective product (the lamp has reached its lifespan). According to this standard, it is determined that the sample number S1 has reached its lifespan in terms of the amount of distortion, and the sample numbers S2 to S12 have not yet reached their lifespan in terms of the amount of distortion, and in particular, it is determined that the lamp is not affected by distortion in terms of the sample numbers S3 to S12.

[0046] From the above, it can be seen that it is good for the elevation angle θ1 to be 50.0 degrees or more and 62.0 degrees or less, and it is more preferable for the elevation angle θ1 to be 53.0 degrees or more and 61.7 degrees or less. For the approximate value P1 (= [(A1 B1) / (C1 D1)] 100), it is good for P1 to be 1.0% or more and 20.0% or less, it is good for P1 to be 1.7% or more and 20.0% or less, and it is preferable for P1 to be 15.0% or less.

[0047] [Other embodiments] The inventors considered that, in addition to the above-mentioned approximate value P1, a parameter related to the elongation and slenderness of the anode 3 would affect the gas flow in the upper space U1 (see FIG. 2B) of the arc tube 1. Therefore, a parameter P2 was calculated that reflects the ratio of the body length L1 (mm) to the anode diameter F2 (mm), which is a parameter related to the elongation and slenderness of the anode 3, in the approximate value P1 of the volume ratio. Specifically, the parameter P2 is calculated by the following equation (4).

number

[0048] [Table 4]

[0049] FIG. 5B is a graph showing Table 2 as a scatter plot with the parameter P2 (=[(A1·B1) / (C1·D1)]·[L1 / F2]·100) on the horizontal axis and the elevation angle θ1 on the vertical axis. Straight lines T2 and T3 are each an approximation line of the plot obtained by the least squares method. It can be seen that the slope of the approximation line of the parameter P2 value changes when the elevation angle θ1 is around 50 degrees. As described above, when the elevation angle θ1 is 50 degrees or more, the blackened area is likely to be obtained outside the effective utilization angle A1, so it is preferable that the parameter P2 is 20 or less. In other words, by specifying the design range of the parameter P2, it was possible to find a range that provides a special effect for the elevation angle θ1.

[0050] The above describes an embodiment of the lamp 100. The present invention is not limited to the above embodiment, and various modifications and improvements can be made to the above embodiment without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0051] 1: Light emitting tube 2a: First side pipe 2b:Second side pipe 3: Anode 4 :Cathode 5a: First lead rod 5b: Second lead rod 12a, 12b: Base 100: Lamp A1: Effective use angle AR: Arc B1: Inner diameter of arc tube Ba1, Ba2: Blackened area U1: Upper space m1~m4: monitoring points θ1: Elevation angle θ2: (anode) taper angle

Claims

1. A cathode; an anode disposed opposite the cathode on one axis and having a larger volume than the cathode; an arc tube having the cathode and the anode therein, mercury sealed therein, and exhibiting a rotationally symmetric shape about the axis; a first side tube formed at an anode side end portion close to the anode and a second side tube formed at a cathode side end portion close to the cathode, A short arc type mercury lamp, characterized in that the following formula (1) is satisfied in a cross section passing through the axis. [0010] (In formula (1), A1 (mm): represents the length in the uniaxial direction from the closest position where the light emitting tube is closest to the anode to the anode side end of the light emitting tube, B1 (mm): represents the inner diameter of the light emitting tube at the closest position, C1 (mm): represents the length in the uniaxial direction from the anode side end of the light emitting tube to the cathode side end, and D1 (mm): represents the inner diameter of the light emitting tube at the most bulging position of the light emitting tube.)

2. 2. The short arc type mercury lamp according to claim 1, wherein the following formula (2) is satisfied: [0025] (In formula (2), A1 (mm): length in the uniaxial direction from the closest position where the arc tube is closest to the anode to the anode side end of the arc tube, B1 (mm): inner diameter of the arc tube at the closest position, C1 (mm): length in the uniaxial direction from the anode side end of the arc tube to the cathode side end of the arc tube, D1 (mm): inner diameter of the arc tube at the most bulging position of the arc tube, L1 (mm): length of the anode in the uniaxial direction, and F2 (mm): maximum diameter of the anode.)

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