JP2014096215A - Discharge lamp and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp having excellent bond strength, and to provide a manufacturing method therefor.SOLUTION: A discharge lamp includes a metal foil 31 having first and second surfaces on the front and back, and an electrode 32 connected with the metal foil 31. Welding marks 36 are formed so that the first surface and the electrode 32 overlap at least partially. When viewed from the second surface side 312, the welding mark 36 has an elliptical shape elongated in the axial direction of the electrode 32, and the ratio L1/L2 of a first length L1 in the axial direction and a second length L2 in the direction orthogonal to the axial direction satisfies a relation 1.08≤L1/L2≤1.56.

Description

  Embodiments described herein relate generally to a discharge lamp and a method for manufacturing the same.

  The discharge lamp is a lamp in which an electrode mount is sealed to a seal portion of an arc tube including an arc tube and a seal portion. The electrode mount is composed of a metal foil and an electrode, which can be welded by laser irradiation. In the electrode mount joined by this laser welding, there is a problem that the joining of the metal foil and the electrode is disengaged, and improvement of the joining strength is required.

JP 2012-84454 A Japanese Patent No. 4972172 Japanese Patent No. 4494224 JP 2005-349477 A JP 2004-363014 A

  An object of this invention is to provide the discharge lamp excellent in joining strength, and its manufacturing method.

  The discharge lamp of the embodiment has a light emitting part, a seal part, and an electrode mount. The light emitting part has a discharge space in which a metal halide is enclosed. The seal part is formed at the end of the light emitting part. The electrode mount includes a metal foil having first and second surfaces located on the front and back sides, and an electrode connected to the metal foil. A welding mark is formed so that at least a part of the first surface and the electrode overlap each other. The welding mark has an elliptical shape that is long in the axial direction of the electrode when viewed from the second surface side, and the ratio L1 between the first length L1 in the axial direction and the second length L2 in the direction orthogonal to the axial direction. / L2 has a relationship of 1.08 ≦ L1 / L2 ≦ 1.56.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge lamp excellent in joining strength and its manufacturing method can be provided.

FIG. 1 is a diagram showing a discharge lamp according to the first embodiment. FIG. 2 is a cross-sectional view showing the discharge lamp of the first embodiment. FIG. 3 is a diagram illustrating a state when the metal foil of the discharge lamp according to the first embodiment is viewed from the second surface side. FIG. 4 is an enlarged view showing the range A shown in FIG. FIG. 5 is a cross-sectional view showing the electrode mount of the first embodiment. FIG. 6 is a diagram showing a relationship between the occurrence rate of disconnection of the discharge lamp of the first embodiment and L1 / L2. FIG. 7 is a diagram illustrating a method of manufacturing the electrode mount according to the first embodiment. FIG. 8 is an explanatory diagram showing laser irradiation of the electrode mount of the first embodiment. FIG. 9 is a diagram showing another example of the electrode mount. FIG. 10 is a diagram illustrating another example of the electrode mount.

  The discharge lamp according to the embodiment described below includes a light emitting unit 11, a seal unit 12, and an electrode mount 3. The light emitting unit 11 has a discharge space 111 in which a metal halide is enclosed. The seal part 12 is formed at the end of the light emitting part 11. The electrode mount 3 includes a metal foil 31 having a first surface 311 and a second surface 312 located on the front and back sides, and an electrode 32 connected to the metal foil 31. A welding mark 36 is formed so that at least a part of the first surface 311 and the electrode 32 overlap. The welding mark 36 has an elliptical shape that is long in the axial direction of the electrode 32 when viewed from the second surface 312 side, and a first length L1 in the axial direction and a second length L2 in a direction orthogonal to the axial direction. The ratio L1 / L2 is 1.08 ≦ L1 / L2 ≦ 1.56.

  In the discharge lamp according to the embodiment described below, the ratio L2 / W between the second length L2 and the diameter W of the electrode 32 is such that 0.3 ≦ L2 / W ≦ 0.9.

  In the discharge lamp according to the embodiment described below, the diameter W of the electrode 32 is 0.2 mm to 0.4 mm.

  In the discharge lamp according to the embodiment described below, the welding mark 36 is formed so as to extend from the metal foil 31 side to the inside of the electrode 32, and the center line is in the direction perpendicular to the second surface 312. It is inclined with respect to.

  In the discharge lamp manufacturing method according to the embodiment described below, the metal foil 31 and the electrode 32 are arranged so that at least a part of the first surface 311 and the electrode 32 overlap, and then from the second surface 312 side. The overlapping portion is irradiated with a laser beam with an optical axis inclined with respect to the normal direction of the metal foil 31, and the first length L1 in the axial direction of the electrode 32 and the second length L2 in the direction orthogonal to the axial direction are The metal foil 31 and the electrode 32 are welded so as to form a welding mark 36 having a ratio L1 / L2 of 1.08 ≦ L1 / L2 ≦ 1.56.

[First Embodiment]
The first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing a discharge lamp according to the first embodiment. FIG. 2 is a cross-sectional view showing the discharge lamp of the first embodiment. FIG. 3 is a diagram illustrating a state when the metal foil of the discharge lamp according to the first embodiment is viewed from the second surface side.

  The discharge lamp of this embodiment is a metal halide lamp used for a headlamp for an automobile headlamp, and includes an inner tube 1 as an airtight container. The inner tube 1 has an elongated shape, and a substantially elliptical light emitting portion 11 is formed near the center thereof. A plate-like seal portion 12 formed by a pinch seal is formed at both ends of the light emitting portion 11, and a cylindrical portion 14 is continuously formed at both ends via a boundary portion 13. The inner tube 1 is preferably made of a material having heat resistance and translucency, such as quartz glass. Further, the seal portion 12 may be formed in a cylindrical shape by being formed by a shrink seal.

  A discharge space 111 having a substantially cylindrical shape at the center and a taper toward both ends is formed inside the light emitting unit 11. The discharge space 111 is filled with the metal halide 2 and the rare gas. The metal halide 2 is composed of sodium iodide, scandium iodide, zinc iodide, and indium bromide. The combination of the metal halides 2 is not limited to this, and tin and cesium halides may be added.

  Xenon is used as the rare gas. The pressure of the rare gas is 12 atm to 18 atm, desirably 13 atm to 16 atm. Note that the rare gas may be a mixed gas of xenon and neon, argon, krypton, or the like.

  Here, the lamp of the present embodiment is a mercury-free discharge lamp. This “mercury-free” means that it does not substantially contain mercury.

  The electrode mounts 3 are sealed to the seal portions 12 formed on both sides of the light emitting portion 11, respectively. The electrode mount 3 includes a metal foil 31, an electrode 32, a coil 33 and a lead wire 34.

  The metal foil 31 is a thin plate member made of, for example, molybdenum, and includes a flat first surface 311 and a second surface 312 on the front and back surfaces. Both ends of the flat surface in the short direction have a knife edge shape that gradually decreases in thickness. In the present embodiment, a rough surface 313 is formed on the first surface 311 on the side to which the electrode 32 is connected and the half surface of the second surface 312 (excluding the overlapping portion between the end portion and the electrode 32). Has been. FIG. 4 is an enlarged view showing the range A shown in FIG. As shown in FIG. 4, the rough surface 313 includes a plurality of circular recesses 3131. The recess 3131 is, for example, a non-penetrating semicircular recess having a diameter of 18 μm and a depth of 3 μm, and can be formed by irradiation with a YAG laser.

  The electrode 32 is a rod-shaped member made of so-called triated tungsten in which, for example, tungsten is doped with thorium oxide. One end thereof is connected to the end of the metal foil 31 on the light emitting portion 11 side, and the other end protrudes into the discharge space 111 and is opposed so as to face each other at a predetermined distance. The diameter W is 0.2 mm to 0.4 mm. Here, when the diameter W is less than 0.2 mm, the temperature of the electrode 32 at the time of lighting becomes high, and the scattering (sputtering) of the electrode material into the discharge space 111 increases. The life characteristics are deteriorated. In addition, if the diameter W exceeds 0.4 mm, the distortion (stress) of the sealing portion between the inner tube 1 and the electrode 32 increases, so that the inner tube 1 is cracked during manufacture of the discharge lamp or during lighting. This may be one of the causes of non-lighting. In the present embodiment, the diameter W is, for example, 0.38 mm. In the case of an automotive headlamp application, the distance between the tips of the electrodes 32 is preferably positioned in the range of 3.7 mm to 4.4 mm when observed through the outer tube 5.

  The coil 33 is a metal wire made of, for example, doped tungsten, and is spirally wound around the axis of the shaft portion of the electrode 32 sealed to the seal portion 12.

  The lead wire 34 is a metal wire made of molybdenum, for example. One end of the lead wire 34 is connected to the end of the metal foil 31 opposite to the electrode connection side from the light emitting portion 11, and the other end extends substantially parallel to the tube axis to the outside of the inner tube 1. ing. One end of an L-shaped support wire 35 made of nickel, for example, is connected to the lead wire 34 extending distally from the front side of the lamp, that is, the socket 6 by laser welding. For example, a sleeve 4 made of ceramic is attached to the support wire 35 at a portion extending in parallel with the inner tube 1.

  On the outside of the inner tube 1 configured as described above, a cylindrical outer tube 5 is provided substantially concentrically with the inner tube 1 so as to cover the light emitting portion 11. These inner and outer pipes are connected by welding the end portions of the outer pipe 5 in the vicinity of the cylindrical portion 14 of the inner pipe 1. Gas is sealed in a closed space 51 formed between the inner tube 1 and the outer tube 5. As this gas, a gas capable of dielectric barrier discharge, for example, one kind of gas selected from neon, argon, xenon and nitrogen or a mixed gas can be used. The gas pressure is desirably 0.3 atm or less, particularly 0.1 atm or less. The outer tube 5 is preferably made of a material having a thermal expansion coefficient close to that of the inner tube 1 and having an ultraviolet blocking property. For example, quartz glass to which an oxide such as titanium, cerium, or aluminum is added is used. can do.

  A socket 6 is connected to one end of the inner tube 1 to which the outer tube 5 is connected. These connections are made by attaching a metal band 71 to the outer peripheral surface of the outer tube 5 and holding the metal band 71 with four metal tongues 72 projecting from the socket 6. Further, a bottom terminal 81 is formed at the bottom of the socket 6, and a side terminal 82 is formed at the side, and a lead wire 34 and a support wire 35 are connected to the bottom terminal 81 and the side terminal 82, respectively. .

  The discharge lamp (foil seal lamp) constituted by these is connected to a lighting circuit (not shown) so that the bottom terminal 81 is on the high voltage side and the side terminal 82 is on the low voltage side. The lamp is lit so that the power of the lamp is 75 W and the stable lighting is 35 W.

Here, the connection between the metal foil 31 and the electrode 32 will be described. In the present embodiment, the metal foil 31 and the electrode 32 are welded at two locations in a state where at least a part of the first surface 311 and the electrode 32 is overlapped. FIG. 5 is a cross-sectional view showing the electrode mount of the first embodiment. As shown in FIG. 5, weld marks 36 and recesses 37 are formed at the welded portions by welding so as to extend from the metal foil 31 side to the inside of the electrode 32 in the overlapping portions. Each welding mark 36 has a substantially elliptical cone shape. The shape when viewed from the second surface 312 side is an elliptical shape that is long in the axial direction of the electrode 32 as shown in FIG. Here, in the elliptical shape, it is sufficient that the first length L1 in the axial direction is longer than the second length L2 in the direction orthogonal to the axial direction, and the outline is configured by a curve. An elliptical shape is also included. Each welding mark 36 is formed such that the ratio L1 / L2 between the first length L1 and the second length L2 is expressed by the following equation (1).
1.08 ≦ L1 / L2 ≦ 1.56 (1)

  FIG. 6 is a diagram showing a relationship between the occurrence rate of disconnection of the discharge lamp of the first embodiment and L1 / L2. As shown in FIG. 6, the rate of occurrence of disconnection (%) greatly varies between the ratio L1 / L2 of the welding marks 36 between 1.00 and 1.08. When the weld mark 36 has a ratio L1 / L2 of 1.00 or less (the shape when viewed from the second surface 312 side is an ellipse that is long in a direction perpendicular to the circle and the axial direction of the electrode 32), the ratio L1 / L2 is Compared to 1.08, the rate of occurrence of disconnection increases rapidly (in the figure, about 9 times). Therefore, by setting the ratio L1 / L2 of each welding mark 36 to 1.08 or more, it is possible to remarkably suppress the disconnection compared to less than 1.00. Similarly, the occurrence rate (%) of the disconnection greatly varies between the ratios L1 / L2 of the welding marks 36 between 1.56 and 1.64. When the weld mark 36 has a ratio L1 / L2 of 1.64 or more (an elliptical shape in which the shape when viewed from the second surface 312 side is considerably longer in the axial direction than the direction orthogonal to the axial direction of the electrode 32), the ratio L1 Compared with / L2 of 1.56 (the first length L1 is about 1.5 times the second length L2), the rate of occurrence of joint detachment increases rapidly (about 6 times in the figure). Therefore, by setting the ratio L1 / L2 of each welding mark 36 to 1.56 or less, it is possible to significantly suppress the disconnection compared to 1.64 or more. In this embodiment, the ratio L1 / L2 is 1.32 (first length L1 = 330 μm, second length L2 = 250 μm), but the ratio L1 / L2 is 1.16 to 1.48. Is more preferable.

Each welding mark 36 is formed such that the ratio L2 / W of the second length L2 and the diameter W of the electrode 32 is expressed by the following equation (2). Here, if the ratio L2 / W is less than 0.3, the welding strength is weakened, and the defect rate such as the disconnection is increased. Further, when the ratio L2 / W exceeds 0.9, welding is performed in a state where a gap is generated between the electrode 32 and the metal foil 31, so that only the metal foil 31 is melted by the heating at the time of welding and the like is perforated. Defects occur. In the present embodiment, the ratio L2 / W is, for example, 0.66.
0.3 ≦ L2 / W ≦ 0.9 (2)

  As shown in FIG. 5A, the shape of each weld mark 36 in the cross section along the short direction of the metal foil 31 is center lines B1-B1 ′ and B2-B2 ′ (most of the electrodes 32 of the weld mark 36). A line that passes through the vicinity of the apex located inside and substantially bisects the area of the welding mark 36 has a substantially triangular shape that is substantially parallel (including parallel) to the perpendicular direction of the second surface 312. Further, the shape of each weld mark 36 in the cross section along the longitudinal direction of the metal foil 31 is such that the center lines B1-B1 ′ and B2-B2 ′ are perpendicular to the second surface 312 as shown in FIG. It has a substantially triangular shape that is substantially parallel to the direction. That is, the inclination angles α1 and α2 are, for example, 0 ° in the present embodiment. The metal foil 31 and the lead wire 34 have the same structure.

  Next, a method for welding the metal foil 31 and the electrode 32 will be described. FIG. 7 is a diagram illustrating a method of manufacturing the electrode mount according to the first embodiment. FIG. 8 is an explanatory diagram showing laser irradiation of the electrode mount of the first embodiment. First, as shown in FIG. 7, the electrode 32 and the lead wire 34 are arranged on the jig 91 so as to fit in the groove 911. Next, after arranging the metal foil 31 so that the first surface 311 overlaps a part of the electrode 32 and the lead wire 34, the holding members 92 are arranged at the four corners of the second surface 312 to dispose the metal foil 31. Fix it. Then, as shown in FIG. 8, the laser irradiation unit 93 of the YAG laser irradiation apparatus irradiates the overlapping portion of the metal foil 31 and the electrode 32 from the second surface 312 side. In the laser irradiation section 93, the optical axes D1-D1 ′ and D2-D2 ′ at the respective welding locations (positions where the respective welding marks 36 are formed) are arranged in the longitudinal direction of the metal foil 31 as shown in FIG. When viewed from the side, it is substantially parallel to the normal direction of the second surface 312, and as shown in FIG. 8B, the normal direction of the second surface 312 is viewed from the short direction of the metal foil 31. The laser beam is irradiated so as to be substantially parallel to. The optical axis inclination angles β1 and β2 are, for example, 0 ° in the present embodiment. This laser irradiation process is performed a plurality of times at different positions, twice in the present embodiment, and two welding marks 36 are formed in the overlapping portion of the metal foil 31 and the electrode 32. Here, the laser irradiation unit 93 can change the laser irradiation range to an elliptical shape as well as a circular shape, and the irradiation range in which the ratio L1 / L2 of the welding marks 36 is in the relationship of the above equation 1, The overlapping portion of the metal foil 31 and the electrode 32 is irradiated with laser from the second surface 312 side.

  In addition, each welding mark 36 may have the center lines B <b> 1-B <b> 1 ′ and B <b> 2-B <b> 2 ′ inclined with respect to the normal direction of the second surface 312. FIG. 9 is a diagram showing another example of the electrode mount. For example, as shown in FIG. 9A, the center lines B <b> 1-B <b> 1 ′ and B <b> 2-B <b> 2 ′ are formed on the second surface 312 as shown in FIG. It is a substantially triangular shape that is substantially orthogonal. Moreover, the shape in the cross section along the longitudinal direction of the metal foil 31 of each welding mark 36 is centerline B1-B1 ', B2-B2' is perpendicular to the 2nd surface 312 as shown in FIG.9 (b). It has a substantially triangular shape inclined with respect to the direction. Compared with the case where the center lines B1-B1 'and B2-B2' of each welding mark 36 described above are substantially parallel to the perpendicular direction of the second surface 312, the joint strength can be improved. The inclination angles α1 and α2 are each 35 °, for example. The inclination angles α1 and α2 are preferably 10 ° to 50 ° in order to further improve the bonding strength. Further, the apex of the recess 37 is unevenly distributed in the direction opposite to the direction in which the welding mark 36 is inclined. Here, when the center lines B <b> 1-B <b> 1 ′ and B <b> 2-B <b> 2 ′ are inclined with respect to the normal direction of the second surface 312 to form the welding marks 36, when viewed from the longitudinal direction of the metal foil 31. The laser is irradiated so as to be substantially orthogonal to the second surface 312 and inclined with respect to the normal direction of the second surface 312 when viewed from the short direction of the metal foil 31. The optical axis inclination angles β1 and β2 are, for example, 35 °. The optical axis tilt angles β1 and β2 are preferably 10 ° to 50 ° in order to further improve the bonding strength. In addition, when the laser irradiation range by the laser irradiation unit 93 is circular, the ratio L1 / L2 of each welding mark 36 is the second surface 312 of the optical axes D1-D1 ′ and D2-D2 ′ at each welding point. It changes according to the inclination degree with respect to the perpendicular direction. Accordingly, the optical axes D1-D1 'and D2-D2' at the respective machining locations are determined so that the ratio L1 / L2 is in the relationship of the above formula 1.

  In this way, by irradiating the laser to the overlapping portion of the metal foil 31 and the electrode 32 obliquely, the shape of the welding mark 36 viewed from the second surface 312 side becomes an elliptical shape. The size becomes larger compared to the circular welding mark formed when the laser is irradiated perpendicularly to the second surface 312 (conventional method). When the size is increased, the contact area between the electrode 32 and the welding mark 36 is increased, so that the bonding strength between the metal foil 31 and the electrode 32 can be enhanced.

  In order to enhance the bonding strength between the metal foil 31 and the electrode 32 by a conventional method, a method of increasing the laser output has been generally used. In the case of this method, damage to the electrode is increased, and the crystal becomes coarse and brittle. Moreover, there is a possibility that the electrode breaks due to the height h of the welding mark 36 inside the electrode 32 being too high. Although there is a method of increasing the laser irradiation diameter, the usable laser irradiation diameter depends on the diameter of the electrode, so that the laser irradiation diameter cannot be increased in some cases. In contrast, the method of the present embodiment can enhance the bonding strength between the metal foil 31 and the electrode 32 while suppressing the occurrence of the above problems without increasing the laser output.

  In the first embodiment, a laser is applied to the overlapping portion from the second surface 312 side in a state where the overlapping portion of the metal foil 31 and the electrode 32 is inclined with respect to the normal direction of the second surface 312. , The overlapped portion is elliptical when viewed from the second surface 312 side, and the center line B1-B1 ′, with respect to the perpendicular direction of the second surface 312 A welding mark 36 in which B2-B2 ′ is inclined can be formed. Therefore, the bonding strength between the metal foil 31 and the electrode 32 can be enhanced without increasing the laser output.

  The present invention is not limited to the above embodiments, and various modifications are possible.

  For example, the material of the metal foil 31 is not limited to molybdenum, and the effect of the present invention can be obtained even if it is composed of rhenium molybdenum, tungsten, rhenium tungsten, etc., and is not limited to the material. Moreover, what formed the thin film and layer on the surface may be used.

  The shape of the electrode 32 is a stepped shape in which the diameter of the distal end is larger than the diameter of the proximal end, a shape in which the distal end is a spherical shape having a large diameter, and one electrode diameter is different from the other electrode diameter. Also good. The electrode material may be pure tungsten, tungsten doped with aluminum, silicon, or potassium in a small amount, rhenium tungsten doped with rhenium in tungsten, or the like.

  FIG. 10 is a diagram illustrating another example of the electrode mount. As shown in FIG. 10A, the center lines B <b> 1-B <b> 1 ′ and B <b> 2-B <b> 2 ′ are perpendicular to the second surface 312. You may make it the shape inclined with respect to. Also, as shown in FIG. 10B, the shape of the weld mark 361 in the cross section along the longitudinal direction of the metal foil 31 has a center line B <b> 1-B <b> 1 ′ with respect to the perpendicular direction of the second surface 312. The shape of the weld mark 362 in the cross section along the longitudinal direction of the metal foil 31 may be a shape in which the center line B2-B2 ′ is inclined toward the lead wire 34 with respect to the perpendicular direction of the second surface 312. Good. In this shape, since the welding marks 361 and 362 hold the electrode 32, it is possible to further suppress the disconnection.

  In addition, the shape of each weld mark 36 in the cross section along the short direction of the metal foil 31 is inclined such that the center lines B1-B1 ′ and B2-B2 ′ intersect with each other across the perpendicular direction of the second surface 312. You may make it the shape. In addition, the shape of each welding mark 36 in the cross section along the longitudinal direction of the metal foil 31 may have different inclination angles α1 and α2.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 1 Inner pipe | tube 11 Light emission part 12 Sealing part 3 Electrode mount 31 Metal foil 32 Electrode 36 Welding trace

Claims (5)

A light emitting part having a discharge space in which a metal halide is enclosed;
A seal portion formed at an end of the light emitting portion;
An electrode mount having a metal foil having first and second surfaces located on the front and back, and an electrode connected to the metal foil;
Have
A welding mark is formed so that at least a part of the first surface and the electrode overlap,
The welding mark has an elliptical shape that is long in the axial direction of the electrode when viewed from the second surface side, and the first length L1 in the axial direction and the second length in a direction orthogonal to the axial direction. The ratio L1 / L2 to L2 is a discharge lamp having the relationship of the following formula (1).
1.08 ≦ L1 / L2 ≦ 1.56 (1) The discharge lamp according to claim 1, wherein
The ratio L2 / W between the second length L2 and the diameter W of the electrode is a discharge lamp having a relationship of the following formula (2).
0.3 ≦ L2 / W ≦ 0.9 (2) The discharge lamp according to claim 1 or 2,
A discharge lamp having a diameter W of 0.2 to 0.4 mm. In the discharge lamp according to any one of claims 1 to 3,
The discharge mark is formed so that the welding mark extends from the metal foil side to the inside of the electrode, and a center line is inclined with respect to a direction perpendicular to the second surface. A light emitting part having a discharge space in which a metal halide is enclosed;
A seal portion formed at an end of the light emitting portion;
An electrode mount having a metal foil having first and second surfaces located on the front and back, and an electrode connected to the metal foil;
In a method of manufacturing a discharge lamp having
After arranging the metal foil and the electrode so that at least a part of the first surface and the electrode overlap, the overlapping portion from the second surface side to the perpendicular direction of the metal foil The laser beam is irradiated with the inclined optical axis, and the ratio L1 / L2 between the first length L1 in the axial direction of the electrode and the second length L2 in the direction orthogonal to the axial direction is expressed by the following equation (3). A method for manufacturing a discharge lamp, wherein the metal foil and the electrode are welded so as to form a welding mark as a relation.
1.08 ≦ L1 / L2 ≦ 1.56 (3)

Images