JP4887547B2 - Lighting device - Google Patents

Description

  The present invention relates to an illumination device for performing linear illumination.

Conventionally, for example, a so-called linear light source device has been used as a light source for a scanner or the like.
The illumination device according to Patent Document 1 is configured as shown in FIG.

  That is, in FIG. 11, the illuminating device 1 has a light source 2 that irradiates light, a condensing unit 3 that condenses the light emitted from the light source 2, and the light condensed by the condensing unit 3 in an elongated shape. The light beam shaping means 4 for shaping and the light projecting means 6 for projecting the elongated light shaped by the light beam shaping means 4 onto the projection object 5 are configured.

The light source 2 is a linear light source extending in the longitudinal direction (perpendicular to the paper surface).
In the illustrated case, the light condensing means 3 is configured as a curved reflecting mirror that extends along the longitudinal direction and is curved so as to surround the light source 2 from the rear in the light emitting direction (left side of the paper).
As a result, the light incident on the condensing means 3 from the light source 2 reflects substantially parallel light toward the front of the light irradiation direction (right side of the paper) by the condensing means.

In the illustrated case, the light beam shaping means 4 is composed of a plate-shaped light shielding member having a slit 4a extending in the longitudinal direction, and transmits light from the light source 2 and the light collecting means 3 forward in the light irradiation direction. It is supposed to let you.
The light projecting means 6 is a cylindrical lens extending in the longitudinal direction, focuses the light transmitted through the slit 4a, and forms an image on the projection object 5 arranged at a predetermined distance in front of the light irradiation direction. It is supposed to let you.

According to the illuminating device 1 having such a configuration, a part of the light emitted from the light source 2 is directly reflected and the other part is reflected / condensed by the light collecting means 3, and then the light beam shaping means. 4 passes through the slit 4a, is further condensed by the light projecting means 6, and converges on the projection object 5 positioned forward by a predetermined distance.
As a result, the bright and elongated shape of the slit 4a is projected onto the surface of the projection object 5 by the light projecting means 6 and illuminated linearly.
Japanese Patent Application Laid-Open No. 11-064784

By the way, although the purpose of the above-mentioned patent document 1 is to irradiate parallel light without distortion, the irradiation light in a desired direction can be controlled by the cylindrical lens as the light projecting means 6 as shown in FIG. As shown in FIG. 6 , only the light passing through the cross section of the cylindrical lens 6 , that is, the light L 1 incident perpendicularly to the axis C of the cylindrical lens 6 .
When such vertical light L1 enters the cylindrical lens, that is, the light projecting means 6, as shown in FIG. 12B, the optical path length in the cylindrical lens becomes the same as the thickness t of the cylindrical lens, as designed. In addition, a clear irradiation pattern can be obtained.
In this case, the luminance distribution in the direction perpendicular to the longitudinal direction in the irradiation pattern is square as shown in FIG. 12C, and the irradiation pattern has a substantially constant luminance.

  On the other hand, as shown in FIG. 13A, when light is incident on the cylindrical lens obliquely, the optical path length of the oblique light L2 in the cylindrical lens becomes t ′ longer than the thickness t. , Will deviate from the design value. For this reason, no image is formed on the surface of the projection object 5 described above.

Therefore, when such oblique light L2 enters the cylindrical lens, that is, the light projecting means 6, as shown in FIG. 13B, an irradiation pattern in which both side edges in the longitudinal direction are blurred is obtained.
In this case, the luminance distribution in the direction perpendicular to the longitudinal direction in the irradiation pattern becomes a gentle mountain shape as shown in FIG. 13C, and the irradiation pattern is distorted.

Actually, as shown in FIG. 14, the light that has passed through the slit 4 a is emitted radially in the longitudinal direction of the cylindrical lens 6, so that the target parallel irradiation light cannot be held. Therefore, as shown in FIG. 15A, the irradiation pattern is greatly blurred in the width direction (direction perpendicular to the longitudinal direction of the irradiation pattern) in the vicinity of both ends of the cylindrical lens 6. As shown in FIG. 15 (B), the luminance is lowered.

  Further, as shown by arrows in FIG. 16, in the case of the oblique incident light L <b> 3 having a large incident angle in the left-right direction with respect to the cylindrical lens 6, when the incident angle exceeds a certain angle, the incident surface or the exit surface of the cylindrical lens 6 is emitted. The critical angle is exceeded at the surface, and the light is totally reflected at the outer surface of the entrance surface or the inner surface of the exit surface. For this reason, as shown in FIG. 17A, the irradiation pattern is not formed in the vicinity of both ends of the cylindrical lens 6, and the luminance is greatly reduced as shown in FIG. 17B. There is a limit to the size in the longitudinal direction of the irradiation pattern.

  On the other hand, in the illuminating device 1 described above, as shown in FIG. 18, for example, when a non-linear light source such as a point light source (slit) 4b is used, as the incident angle increases, as shown in FIG. As shown in A), the blur of the irradiation pattern increases and the width increases. Further, in the region where the incident angle is large, as shown in FIG. 19B, the brightness is drastically lowered, and the irradiation pattern cannot be formed correctly.

  On the other hand, when a linear light source is used as the light source, in order to obtain the above-described normal incident light, it is necessary to configure the linear light source with substantially the same length as the projection object. Since the light source is enlarged, the cost is increased.

  In view of the above, an object of the present invention is to provide an illumination device that forms a linear irradiation pattern in a wide range using a small light source with a simple configuration.

  According to the present invention, the above object includes a light source and a lens formed of at least a part of a shape obtained by sweeping a predetermined design cross section in an arc shape protruding to the opposite side of the light source. This is achieved by the lighting device.

  The illumination device according to the present invention preferably has a shape in which the design cross section of the lens is spherical or aspheric on one or both sides.

  In the illumination device according to the present invention, preferably, a shielding member having a long opening extending substantially parallel to the sweeping direction of the lens is disposed between the light source and the lens.

In the illuminating device according to the present invention, preferably, the shielding member has a substantially similar cross section with respect to the sweep locus of the lens.
The opening of the shielding member of the lighting device according to the present invention is preferably set to a small size in order to obtain a clearer irradiation pattern.

  In the lighting device according to the present invention, the opening is preferably rectangular or trapezoidal.

  In the illuminating device according to the present invention, preferably, the opening is formed such that the width gradually decreases toward the end edge in the longitudinal direction.

In the illumination device according to the present invention, preferably, the opening is formed asymmetrically with respect to a plane including a sweep locus of the lens.
The illuminating device according to the present invention preferably takes structural considerations such that, for example, the longitudinal dimension of the opening is shortened, light components having different optical path lengths are reduced when the light beam enters the lens surface.

  The illumination device according to the present invention preferably includes a housing for fixing and holding the light source, the light shielding member, and the lens.

  In the illumination device according to the present invention, preferably, at least one of both end portions in the longitudinal direction of the lens is fixed to the housing by a bolt.

  In the illuminating device according to the present invention, preferably, at least one of both end portions in the longitudinal direction of the lens is provided with a hook having an inverted spine shape, and the hook engages with a fixing hole provided in the housing. , Fixed to the housing.

  In the illumination device according to the present invention, preferably, at least one of both end portions in the longitudinal direction of the lens includes a flange portion that contacts the housing surface.

According to the above configuration, the lens has an upwardly convex arc shape, and light incident obliquely from the light source (light corresponding to the conventional oblique light L2 (see FIG. 13)) is coupled by the condensing function of the lens. Is greatly reduced. Thereby, distortions such as blurring and spreading of the irradiation pattern can be greatly reduced, and a desired irradiation pattern can be formed.

In addition, since the incident angle of light obliquely incident on the lens from the light source can be made smaller than the critical angle, total reflection on the outer surface of the lens can be suppressed, and the light is emitted when passing through the lens and then exiting the lens. By making the incident angle smaller than the critical angle on the surface, total reflection on the inner surface of the lens can be suppressed.
Therefore, the light extraction efficiency from the lens is improved, and an irradiation pattern can be formed with a relatively high luminance corresponding to the area near both ends of the lens, and a longer irradiation pattern can be obtained as a whole. Become.
As a result, even if the light source is a point light source or a linear light source shorter than the length of the lens in the longitudinal direction, an elongated irradiation pattern extending over almost the entire length of the lens can be formed via the lens.

  When the design cross section of the lens has a shape that is spherical or aspheric on one or both sides, the lens has a convex shape in the width direction perpendicular to the longitudinal direction of the lens, and focuses the light from the light source. It will be.

When a shielding member having a long opening extending substantially parallel to the lens sweep direction is disposed between the light source and the lens, an image of the opening (slit) of the shielding member is projected by the lens. It is projected onto an object or the like.

  When the shielding member has a substantially similar cross section with respect to the sweep trajectory of the lens, the opening of the shielding member is disposed at substantially the same distance from the lens at each part, and the opening is formed by the lens. Projected. Thereby, a correct irradiation pattern can be formed.

When the opening is rectangular or trapezoidal, an image of the opening (slit) is projected by the lens. Thereby, a rectangular or trapezoidal irradiation pattern is formed.

  When the opening is formed so that the width is gradually narrowed toward the edge in the longitudinal direction, the opening tends to be narrowed near both ends, so that the width tends to be wide near both ends. The irradiation pattern can be formed with substantially the same width in the vicinity of both ends.

  When the opening is formed asymmetrically with respect to the surface including the sweep trajectory of the lens, it is possible to form an irradiation pattern only on one side, for example, as a cut-off in a vehicle headlamp. It is.

  In the case where a housing for fixing and holding the light source, the light shielding member, and the lens is provided, the light source, the light shielding member, and the lens can be accommodated in the housing. Thereby, it can protect from dust, dust, etc., and it can be comprised so that the light from a light source may not leak about an unnecessary direction outside.

  At least one of both end portions in the longitudinal direction of the lens is fixed to the housing by a bolt, or has an inverted spine-shaped hook, and the hook engages with a fixing hole provided in the housing. When the lens is fixed to the housing, the lens can be easily and reliably fixed and held to the housing by bolting or hook engagement.

  When at least one of both end portions in the longitudinal direction of the lens includes a flange portion that comes into contact with the housing surface, the lens can be reliably positioned and held with respect to the housing surface. In addition, the flange portion can be easily and securely fixed and held by screwing, engaging or the like with the housing.

  Thus, according to the present invention, there is provided an illumination device that forms a linear irradiation pattern in a wide range using a small light source with a simple configuration.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

[Example 1]
1 to 3 show a configuration of a first embodiment of a lighting device to which the present invention is applied.
1 to 3, the illumination device 10 includes a housing 11, a light source 12, a light shielding member 13, and a lens 14. Hereinafter, in order to clarify the relative positional relationship of these components, an XYZ coordinate system is defined (see FIG. 3 and the like).

  The housing 11 is formed of a non-translucent material in a substantially rectangular parallelepiped shape, and has a substantially rectangular parallelepiped hollow portion 11a opened upward.

The light source 12 is composed of at least one (three in the illustrated case) light emitting element, for example, an LED 12b, mounted on the printed circuit board 12a in the hollow portion 11a of the housing 11.
Here, the LEDs 12b constituting the light source 12 are arranged in a line along the longitudinal direction ( X direction ) near the center of the hollow portion 11a of the housing 11.
The printed circuit board 12a is fixed and held to the bottom of the hollow portion 11a of the housing 11 by adhesion or the like.

The light shielding member 13 is made of a plate-like opaque material and is attached to the upper end of the housing 11 so as to close the open end of the hollow portion 11a of the housing 11.
Further, the light shielding member 13 includes a slit 13a as an opening having an elongated rectangular or trapezoidal shape extending in the longitudinal direction (X direction) in the vicinity of the center thereof. In the illustrated case, the slit 13a is located immediately above each LED 12a of the light source 12, and the length thereof corresponds to the arrangement length of each LED 12a.
In this example, a slit width of 1 mm and a slit length of 14 mm were employed. In addition, the width of the housing 11 in this embodiment was 40 mm and the length was 60 mm.

5, the lens 14 has a flat bottom surface 14c (corresponding to the inner surface of the present invention, see FIGS. 4 and 5) and an upper surface 14d (corresponding to the outer surface of the present invention ) . 4 and FIG. 5) is formed as a single-sided cylindrical lens formed in a convex shape in the + Z direction by a spherical surface or an aspherical surface. Moreover, as shown in the cross-sectional view of FIG. 4, it is curved in a convex arc shape upward (+ Z direction) with respect to the longitudinal direction (X direction) . The convex arc-shaped lens width (Y direction) is 20 mm in this embodiment, and the arc-shaped diameter is about 44 mm.
The lens 14 has a shape obtained by sweeping the crescent-shaped cross-sectional shape in the cross-sectional view of FIG. 5 into an arc as shown in FIG.
Here, the arc-shaped sweep curve is preferably represented by an arc shape or an aspherical approximate expression.

In FIG. 5, the lower focal position of the lens 14 is located near the slit 13 a of the light shielding member 13.
Thus, a sharp irradiation pattern is formed by projecting the shape of the slit 13a (image of the slit 13a) by the lens 14.

Further, both ends of the lens 14 curved downward are fixedly held with respect to both ends in the longitudinal direction (X direction) of the housing 11 via the light shielding member 13.
Thereby, the light source 12, the light shielding member 13, and the lens 14 can be fixedly held by the housing 11.

As shown on the left side of FIG. 6A, the lens 14 has a flange portion 14a projecting outward from at least one end thereof to the light-shielding member 13 with a fixing screw 15a from below or a fixing screw from above. 15b, or as shown on the right side of FIG. 6 (A), an inverted spine-shaped hook 14b provided directly on at least one end of the hook 14b is provided in the engagement hole 13b provided on the light shielding member 13. It is fixed by engaging.
On the other hand, as shown on the left side of FIG. 6 (B), the lens 14 may be screwed to the lower surfaces of both ends from below with fixing screws 15c.

The lighting device 10 according to the embodiment of the present invention is configured as described above, and operates as follows.
That is, each LED 12b of the light source 12 is driven to emit light. The light emitted from each LED 12b passes through the slit 13a of the light shielding member 13 and then enters the lens 14. The optical direction of the lens 14 causes the width direction (the width direction of the lens or the width direction of the slit, that is, Y). Direction) and exit to the outside.
Thereby, the image of the slit 13a is projected by the lens 14, and an irradiation pattern is formed.

In this case, when the light emitted radially from each LED 12b through the slit 13a in the longitudinal direction (X direction) enters the lower surface 14c of the lens 14, as shown in FIG. The surface 14c is convexly convex upward (+ Z direction) , and therefore the incident angle is reduced.
As a result, the light passing through the lens 14 does not significantly differ in the optical path length in the lens 14 and passes through the lens 14 under almost design conditions. This ensures that an image is formed on the surface of the projection object (not shown).
Therefore, as shown in FIG. 7B, the irradiated light diffuses in the width direction (the width direction of the lens or the width direction of the slit, ie, the Y direction) near both side edges in the longitudinal direction (X direction) . Therefore, a blurred irradiation pattern is not formed in the width direction (the width direction of the lens or the width direction of the slit, ie, the Y direction) , and a clear irradiation pattern is obtained.

In addition, since the incident angle to the lens 14 is relatively small, light (conventional oblique light L2 (conventional oblique light L2 )) is incident on the lens 14 obliquely from each LED 12b of the light source 12 near both ends in the longitudinal direction (X direction). 13) is incident on the inner outer surface and the outer inner surface of the lens 14 at an incident angle smaller than the critical angle. For this reason, there is no such thing as total reflection on the outer and inner surfaces. Therefore, as described above, the light extraction efficiency from the lens 14 to the outside is improved in combination with the suppression of diffusion near both ends in the longitudinal direction (X direction) of the irradiation pattern. Thereby, as shown in FIG. 7C, the luminance of the irradiation pattern can be kept relatively high in a relatively wide angle range.

[Example 2]
FIG. 8 shows an irradiation state according to the configuration of the second embodiment of the illumination device according to the present invention.
In this second embodiment, the illumination device has the same configuration as the illumination device shown in FIGS. 1 to 3, but instead of the light source 12 , it comprises a point light source 21, for example, a single LED. The configuration differs only in that a light source is provided.

According to this configuration, as shown in FIG. 8A, the light emitted radially from the light source 21 is almost perpendicular to the inner surface 14c of the lens 14, that is, the incident angle. Is incident at almost zero.
Therefore, almost all the light is transmitted to the lens 14 under the design conditions and receives an optical action. For this reason, as shown in FIG. 8B, a desired irradiation pattern can be formed.
Accordingly, as shown in FIG. 8C, relatively high luminance can be obtained in a wide angle range with respect to the longitudinal direction (X direction) .

[Example 3]
FIG. 9 shows a configuration example of the light shielding member in the third embodiment of the illumination device according to the present invention.
In this third embodiment, the illumination device has the same configuration as the illumination device shown in FIGS. 1 to 3, but differs only in that a light shielding member 31 is provided instead of the light shielding member 12. It has become.
The light shielding member 31 is formed such that a slit 31a provided in the vicinity of the center and extending in the longitudinal direction (X direction) is gradually narrowed toward both ends.

According to the illuminating device having such a configuration, it operates in the same manner as the illuminating device shown in FIGS. 1 to 3, and the slit 31a of the light shielding member 31 is narrowed in the width direction (Y direction) near both ends. . Thereby, the width of the image of the slit 31a with respect to the light source 11 can be made uniform.
Therefore, diffusion near the both ends of the irradiation pattern is more reliably suppressed, and an irradiation pattern with even less distortion can be obtained.

[Example 4]
FIG. 10 shows a configuration example of the light shielding member in the fourth embodiment of the illumination device according to the present invention.
In the fourth embodiment, the illumination device has the same configuration as the illumination device shown in FIGS. 1 to 3, but differs only in that a light shielding member 41 is provided instead of the light shielding member 12. It has become.
The light shielding member 41 has a slit 41a provided in the vicinity of the center thereof extending from the center line in the longitudinal direction (X direction) to one side with respect to the center line (that is, the XZ plane) in the longitudinal direction (X direction). And asymmetrically formed.

According to the illuminating device having such a configuration, it operates in the same manner as the illuminating device shown in FIGS. 1 to 3 so that the slit 41a of the light shielding member 41 extends from the center line in the longitudinal direction (X direction) to one side. Is formed. For this reason, the side edge of the slit 41a forms a cut-off line with respect to the irradiation pattern.
Therefore, an illuminating device having a cut-off line, for example, an illuminating device optimal as a low-beam vehicle headlamp can be realized.

In the embodiment described above, the light source 12 is composed of a plurality of LEDs arranged in a row, but may be composed of a single LED, or a point light source such as another light emitting element. It may be.
In the above-described embodiment, the light source 12 is configured by an LED as a light emitting element. However, the light source 12 is not limited to this, and is not limited to this. A tube or the like may be used.

Furthermore, in the above-described embodiment, a plurality of LEDs are arranged in a line to form a linear light source. However, the present invention is not limited to this, and in order to adjust the intensity distribution and irradiation position of the irradiation pattern, It is also possible to dispose the point light sources such as the LEDs as shifted in the longitudinal direction (X direction) or the width direction (Y direction) .

In the embodiment described above, in order to focus the light from the light source 12 in the width direction (Y direction) perpendicular to the longitudinal direction (X direction) of the lens 14, the lens 14 has a cross-sectional shape (FIG. 5). Although reference) is formed similarly to the single-sided cylindrical lens, not limited thereto, and may be formed similarly to the double-sided cylindrical lens.
At that time, the cross-sectional shape of the lens is not limited to the circular arc (the cross-sectional shape of the spherical lens), but may be the same as the cross-sectional shape of the aspherical lens, or may be formed as a quadratic curve.

  Furthermore, in the above-described embodiment, the lighting device 10 is simply described. However, the lighting device is not limited to this, and examples of the lighting device include vehicle headlamps such as headlamps, auxiliary headlamps such as fog lamps, and so-called AFS. (Adaptive Front-Lighting System) vehicle lamps including bending lamps, vehicle width light source for rear parking assistance system, light source for side vehicle width recognition, light source for scanner reading, for crime prevention, FA (Factor Automation), etc. It is apparent that the present invention can be applied to the light sources for various line sensors.

  As described above, according to the present invention, an extremely excellent illumination device is provided that uses a small light source to form a linear irradiation pattern in a wide range with a simple configuration. .

It is a front view which shows the structure of 1st embodiment of the illuminating device by this invention. It is a top view which shows the illuminating device of FIG. It is a perspective view which shows the illuminating device of FIG. It is a cross-sectional view which follows the longitudinal direction which shows the illuminating device of FIG. It is a longitudinal cross-sectional view which follows the width direction which shows the illuminating device of FIG. FIG. 2 is an enlarged cross-sectional view showing fixing means at both ends of a lens in the illumination device of FIG. 1. It is a longitudinal cross-sectional view which shows the irradiation state of the light from the light source in the illuminating device of FIG. 1, (B) An irradiation pattern, and (C) It is a figure which shows the luminance distribution of a longitudinal direction. It is a longitudinal cross-sectional view which shows the irradiation state of the light from the (A) light source in 2nd embodiment of the illuminating device by this invention, (B) An irradiation pattern, and (C) It is a figure which shows the luminance distribution of a longitudinal direction. It is a top view which shows the light-shielding member in 3rd embodiment of the illuminating device by this invention. It is a top view which shows the light-shielding member in 4th embodiment of the illuminating device by this invention. It is a schematic sectional drawing which shows the structure of an example of the conventional illuminating device. It is a figure which shows the (A) perpendicular | vertical incident state of the light with respect to a lens in the illuminating device of FIG. 11, (B) the irradiation pattern at this time, and the brightness distribution of the (C) width direction. It is a figure which shows the oblique incident state of the light with respect to the lens (A) in the illuminating device of FIG. 11, (B) the irradiation pattern at this time, and (C) the luminance distribution of the width direction. It is a cross-sectional view which shows the irradiation state of the light from the linear light source in the illuminating device of FIG . It is a figure which shows the luminance distribution of (A) irradiation pattern and (B) longitudinal direction in the light irradiation state of FIG. It is a longitudinal cross-sectional view which shows the total reflection in the lens of the light from the linear light source in the illuminating device of FIG. It is a figure which shows the brightness distribution of (A) irradiation pattern and (B) longitudinal direction in the light irradiation state of FIG. It is a longitudinal cross-sectional view which shows the irradiation state of the light from the point light source in the illuminating device of FIG. It is a figure which shows the luminance distribution of (A) irradiation pattern and (B) longitudinal direction in the light irradiation state of FIG.

DESCRIPTION OF SYMBOLS 10 Illuminating device 11 Housing 11a Hollow part 12 Light source 12a Printed circuit board 12b LED (light emitting element)
13 Shading member 13a Slit (opening)
13b Engagement hole 14 Lens 14a Flange part 14b Hook 15a, 15b, 15c Fixing screw

Claims (6)

A light source that emits light in the + Z direction disposed at the origin of the XYZ coordinate system;
An inner side surface having a width in the Y-axis direction, extending in an arc from the negative side on the X axis to the positive side on the Z axis and extending to the positive side on the X axis, and receiving light from the light source; It has a width in the direction, is arranged outside the inner surface, passes from the − side on the X axis to the + side on the X axis, passes through the + side on the Z axis, and extends in an arc shape on the + side on the X axis An arcuate lens that extends in an arc shape convex in the + Z direction from the − side on the X axis to the + side on the X axis as a whole, and an outer surface that emits light from the light source incident from the inner surface.
With
The arcuate lens includes a cross section extending in the Y direction of the inner side surface, and a cross section disposed outside the cross section extending in the Y direction of the inner side surface and extending in the Y direction of the outer side surface, and from the light source A cross section of a convex lens configured to focus incident light in the Y direction passes through the + side on the Z axis from the − side on the X axis without changing its shape, and forms an arc shape on the + side on the X axis. A lighting device characterized by being a lens having a shape swept into   The arcuate lens includes a cross section extending in the Y direction of the inner side surface, and a cross section disposed outside the cross section extending in the Y direction of the inner side surface and extending in the Y direction of the outer side surface, and from the light source A convex lens cross section configured to focus incident light in the Y direction passes through the + side on the Z axis from the-side on the X axis and rotates in an arc around the Y axis from the + side on the X axis. The illumination device according to claim 1, wherein the illumination device is a lens having a swept shape. The lighting device according to claim 1 , wherein the light source is a point light source or a linear light source extending in the X direction. Is disposed between the light source and the arcuate lens, to claim 1, characterized in that it comprises further a shielding plate in which slits are formed extending in the X direction together with the light passes in the + Z direction from the light source The lighting device described. The lighting device according to claim 4 , wherein the slit is formed in a shape in which a width in the Y direction gradually decreases toward an end edge in the X direction. The lighting device according to claim 4 , wherein the slit is formed asymmetrically with respect to the XZ plane.

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