Patent Publication Number: US-8974101-B2

Title: Vehicular lamp

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicular lamp including a light guiding plate. 
     2. Description of the Related Art 
     One of the conventionally known vehicular lamp is constructed so that emitted light from the light-emitting element such as a light-emitting diode is incident on the rear end surface of a light guiding plate and then is emitted from the front end surface of the light guiding plate to the front of the lamp. 
     Japanese Patent Application&#39;Laid-Open (Kokai) No. 2007-280689, for example, describes a lens component formed on the tear end surface of a light guiding plate provided along a horizontal plane in such a vehicular lamp. In this vehicular lamp, the lens component allows emitted light from the light-emitting element to be incident on the light guiding plate as converging light that converges in the forward direction of the light-emitting element. 
     The configuration described in Japanese Patent Application Laid-Open (Kokai) No. 2007-280689 increases the amount of light that is guided in a direction toward the forward direction of the light-emitting element inside the light guiding plate, and thus allows the light guiding plate to appear to be brightly lit when the light guiding plate is observed from the front of the lamp. 
     However, in the light distribution of the emitted light from the light-emitting element, the light traveling in the forward direction of the light-emitting element typically has the highest intensity. Accordingly, adopting the configuration described in Japanese Patent Application Laid-Open (Kokai) No. 2007-280689 causes such a problem that when the light guiding Plate is observed from the front of the lamp, only a portion close to the light-emitting element appears extremely brightly lit, and as a result, the light guiding plate cannot be made to appear to be lit in a substantially uniform manner due to this so-called point lighting phenomenon. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention was developed in view of the above problem, and it is an object of the present invention to provide a vehicular lamp that includes a light guiding plate and that allows the light guiding plate to appear brightly lit in a substantially uniform manner. 
     The present invention achieves the above object with a configuration that a predetermined lens member is provided between a light-emitting element and a light guiding plate. 
     More specifically, above-described object is accomplished by a unique structure of the present invention for a vehicular lamp that includes: a light-emitting element and a light guiding plate provided such that emitted light from the light-emitting element is incident on the rear end surface of the light guiding plate and then is emitted from the front end surface of the light guiding plate to the front of the lamp, and the vehicular lamp of the present invention further includes a lens member that is provided between the light-emitting element and the light guiding plate, and this lens member allows a part of the emitted light from the light-emitting element, which travels in a direction close to the forward direction of the light-emitting element, to reach the light guiding plate as diffusing light that diffuses in a first plane that is along the light guiding plate, and further to allow the emitted light from the light-emitting element to reach the light guiding plate as converging light that converges in the forward direction of the light-emitting element in a second plane that is orthogonal to the first plane. 
     The “light-emitting element” means a light source that is an element having a light-emitting portion that surface-emits light generally in the shape of a spot, and the type of the light-emitting element is not particularly limited. 
     The specific, shape of the “light guiding plate” is not specifically limited as long as the light guiding plate is constructed so that the emitted light from the light-emitting element is incident on the rear end surface of the light guiding plate, and then is emitted from the front end surface of the light guiding plate to the front of the lamp. 
     The “first plane” is any one of a horizontal plane, a vertical plane, and an inclined plane. 
     The specific shape of the “lens member” is not particularly limited as long as the lens member allows a part of the emitted light from the light-emitting element, which travels in the direction close to the forward direction of the light-emitting element, to reach the light guiding plate as diffusing light that diffuses in the first plane and further allows the emitted light from the light-emitting element to reach the light guiding plate as converging light that converges in the forward direction of the light-emitting element in the second plane. The above phrase “converging light that converges in the forward direction of the light-emitting element” refers to the light that is deflected in the direction toward the forward direction of the light-emitting element with respect to the direction of the light that reaches the light guiding plate if there is no lens member, and it is not necessarily the light that travels in the direction parallel to the forward direction of the light-emitting element. 
     As seen from the above in the vehicular lamp according to the present invention the emitted light from the light-emitting element is incident on the rear end surface of the light guiding plate and then is emitted from the front end surface of the light guiding plate to the front of the lamp, and in this construction, a lens member is provided between the light-emitting element and the light guiding plate, and this lens member allows part of the emitted light from the light-emitting element, which travels in the direction close to the forward direction of the light-emitting element, to reach the light guiding plate as diffusing light that diffuses in the first plane that is along the light guiding plate and further allows the emitted light from the light-emitting element to reach the light guiding plate as converging light that converges in the forward direction of the light-emitting element in the second plane that is orthogonal to the first plane. Accordingly, the vehicular lamp according to the present invention provides the effects described below. 
     In the vehicular lamp according to the present invention, the lens member allows a part of the emitted light from the light-emitting element, which travels in the direction close to the forward direction of the light-emitting element, to reach the light guiding plate as diffusing light that diffuses in the first plane that is along the light guiding plate. This can prevent the light that reaches the light guiding plate from having such an intensity distribution that the light intensity becomes extremely high in the forward direction of the light-emitting element in the first plane, and as a result, the light guiding plate can appear to be lit in a substantially uniform manner in a direction along the first plane when the light guiding plate is observed from the front of the lamp. 
     Moreover, in the vehicular lamp according to the present invention, the lens member allows the emitted light from the light-emitting element to reach the light guiding plate as converging light that converges in the forward direction of the light-emitting element in the second plane. Accordingly, the emitted light from the light-emitting element can be efficiently incident on the light guiding plate, and the light guiding plate can appear to be brightly lit when the light guiding plate is observed from the front of the lamp. 
     As seen from the above, according to the present invention, the light guiding plate provided in a vehicular lamp appears to be brightly lit in a substantially uniform manner, thus improving the appearance of the lamp. 
     In the above configuration, the lens member can be constructed so that it allows the emitted light from the light-emitting element to reach the light guiding plate in a luminance distribution that a pair of peak values of luminance appear on both sides of the forward direction of the light-emitting element in the first plane. As a result, the light that reaches the light guiding plate has a more uniform light intensity distribution in the first plane, and thus the light guiding plate can appear to be more uniformly lit in the direction along the first plane when the light guiding plate is observed from the front of the lamp. 
     In the present invention, the rear end surface of the light guiding plate can be formed with a lens component so that the lens component allows the emitted light from the light-emitting element, which has reached the light guiding plate through the lens member, to be incident on the light guiding plate as converging light that converges in the first plane. With this structure, it is easily possible to have the light guiding plate appear to be brightly lit in a substantially uniform manner in the direction along the first plane when the light guiding plate is observed from the front of the lamp. 
     When the front end surface of the light guiding plate is formed to extend to a large extent toward a rear side of the lamp from one end to the other end in the first plane, the emitted light from the light guiding plate cannot be emitted as diffusing light that diffuses in a balanced manner to both sides with respect to the forward direction of the lamp, if a plurality of lens elements are continuously formed on the front end surface of the light guiding plate along the wrap-around shape of the front end surface of the light guiding plate. In order to emit the light from the light guiding plate as diffusing light that diffuses in a balanced manner to both sides with respect to the forward direction of the lamp, the plurality of lens elements need to be formed to face the forward direction of the lamp, with a large step between the lens elements. However, this degrades the appearance of the light guiding plate. 
     Accordingly, when the front end surface of the light guiding plate is formed to extend to a large extent toward the rear side of the lamp from the one end to the other end in the first plane, the rear end surface of the light guiding plate can be formed to face a direction inclined toward the other end with respect to the forward direction of the lamp. This allows the emitted light from the light guiding plate to be emitted as diffusing light that diffuses in a balanced manner to both sides with respect to the forward direction of the lamp, even if the plurality of lens elements are continuously formed along the wrap-around shape of the front end surface of the light guiding plate, thus preventing degradation in appearance of the light guiding plate. 
     In the present invention, the light-emitting element can be provided at a plurality of positions in the first plane, each of the lens member and the light guiding plate can be provided at a plurality of positions corresponding to the plurality of light-emitting elements, the plurality of lens members can be coupled together to form a single lens member unit, and the plurality of light guiding plates can be coupled together to form a single light guiding plate unit. With this structure, the light guiding plates provided at the plurality of positions can appear to be brightly lit in a substantially uniform manner in the direction along the first plane when the light guiding plate unit is observed from the front of the lamp, and this can be implemented with a smaller number of parts. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a horizontally cross-sectional view of a vehicular lamp according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along the line II-II in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along the line III-III in  FIG. 1 . 
         FIG. 4  is a detailed view of the portion  4  in  FIG. 1 . 
         FIG. 5  illustrates the operations of a lens member of the vehicular lamp of the present invention. 
         FIG. 6(   a ) is a front view of a light guiding plate unit when each light-emitting element of the vehicular lamp is lit, and  FIG. 6(   b ) is a view similar to  FIG. 6(   a ) and shows the operations of a conventional lamp. 
         FIG. 7  is a view similar to  FIG. 1  showing a modification of the embodiment of the present invention. 
         FIG. 8(   a ) is a detailed view of a portion  8 ( a ) in  FIG. 7 , and  FIG. 8(   b ) is a view similar to  FIG. 8(   a ) and shows a comparative example. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a horizontally cross-sectional view of a vehicular lamp  10  according to the present embodiment.  FIG. 2  is a cross-sectional view taken along the line II-II in  FIG. 1 ,  FIG. 3  is a cross-sectional view taken along the line III-III in  FIG. 1 , and  FIG. 4  is a detailed view of the portion  4  in  FIG. 1 . 
     As shown in these figures, the vehicular lamp  10  is a front turn signal lamp mounted at the left front end of a vehicle, and it is constructed by incorporating three light-emitting elements  22 , a single light guiding plate unit  16 , and a single lens member unit  18  in a lamp chamber formed by a lamp body  12  and a generally plain translucent cover  14  attached to the front end opening of the lamp body  12 . 
     The translucent cover  14  is formed to extend toward the rear side of the lamp (i.e., the rear side of the vehicle) from the right end toward the left end (in  FIG. 1 , from the left end toward the right end) of the translucent cover  14 . 
     The three light-emitting elements  22  are amber light-emitting diodes, and they are provided so that their light-emitting surfaces  22   a  face the forward direction of the lamp (i.e., the forward direction to the front of the vehicle). These three light-emitting elements  22  are provided at substantially regular intervals in the lateral direction (i.e., the vehicle width direction) on the same horizontal plane and offset from each other so that the light-emitting element  22  located closer to the left side (right side in  FIG. 1 ) is disposed closer to the rear Side of the lamp. These light-emitting elements  22  are fixedly supported by substrates  24 , respectively, and each of the substrates  24  is fixedly supported by the lamp body  12 . 
     The light guiding plate unit  16  is provided on the front side of the lamp with respect to the three light-emitting elements  22 . The front end surface  16   b  of the light guiding plate unit  16  is formed to extend toward the rear side of the lamp from the right end to the left end of the front end surface  16   b  so as to correspond to the wrap-around shape of the translucent cover  14 . This light guiding plate unit  16  is fixedly supported at both left and right ends thereof by the lamp body  12 . 
     The light guiding plate unit  16  is constructed as a single member comprising three light guiding plates  26  coupled together. The three light guiding plates  26  are provided at positions corresponding to the three light-emitting elements  22 , respectively. 
     On the other hand, the lens member unit  18  is provided between the three light-emitting elements  22  and the light guiding plate unit  16 . This lens member unit  18  is fixedly supported at both left and right sides thereof by the lamp body  12 . 
     The lens member unit  18  is constructed as a single member comprising three lens members  28  coupled together, and these three lens members  28  are provided at positions corresponding to the three light-emitting elements  22 , respectively. 
     In the shown embodiment as described above, light emitted from each light-emitting element  22  and deflected and transmitted through each lens member  28  of the lens member unit  18  is incident on each light guiding plate  26  of the light guiding plate unit  16  from the rear end surface  26   a  of each light guiding plate  26 , and then the light is emitted out from the front end surface  26   b  of each light guiding plate  26  to the front of the lamp. 
     Thus, the vehicular lamp  10  according to the shown embodiment is constructed to include three sets of the light-emitting element  22 , the light guiding plate  26 , and the lens member  28  that are provided on an optical axis Ax that extends in the longitudinal (front-rear) direction of the lamp. These three optical systems have similar configurations except that the degree of inclination of the front end surface  26   b  in the lateral direction slightly varies among the light guiding plates  26  according to the wrap-around shape of the front end surface  16   b  of the light guiding plate unit  16  in the lateral direction. 
     The configuration of one of the optical systems will be described in detail below. 
     As shown in  FIG. 2 , the cross-sectional shape of the lens member  28  along a vertical plane including the optical axis Ax is set to a plano-convex aspheric lens shape. In other words, the rear surface  28   a  of the lens member  28  is set to be a convex curve shape, and the front surface  28   b  of the lens member  28  is set to be a linear shape. The rear surface  28   a  of this lens member  28  is constructed as a toric lens surface having as its central axis a vertical line passing through the center of light emission of the light-emitting element  22 . As shown in  FIG. 4 , the cross-sectional shape of the front surface  28   b  of the lens member  28  along a horizontal plane is formed by a concave curve in an area in the proximity of the optical axis Ax, and it is also formed by a convex curve in each of the areas located on both left and right sides of the concave-curve area, and each of the convex curves smoothly connects to the concave curve. 
     With the above structure, the lens member  28  allows a part of emitted light from the light-emitting element  22 , which travels in the direction close to the optical axis Ax, to reach the light guiding plate  26  as diffusing light that diffuses in a horizontal plane and further allows the emitted light from the light-emitting element  22  to reach the light guiding plate  26  as parallel light along the optical axis Ax in a vertical plane. 
     Furthermore, as shown in  FIG. 5 , the cross-sectional shape of the front surface  28   b  of the lens member  28  along the horizontal plane is set so as to allow the emitted light from the light-emitting element  22  to reach the light guiding plate  26  in a luminance distribution that a pair of luminance peak values appear on both left and right sides of the optical axis Ax in the horizontal plane. 
     A Fresnel lens having a vertical ridge and groove pattern is, as best seen in  FIG. 4 , formed as a lens component  26   s   1  on the rear end surface  26   a  of the light guiding plate  26 . This allows the emitted light from the light-emitting element  22 , which has reached the light gliding plate  26  through the lens member  28 , to be incident on the light guiding plate  26  as light parallel to the optical axis Ax in the horizontal plane. 
     As shown in  FIG. 1 , a plurality of diffusion lens elements  26   s   2  are formed on the front end surface  26   b  of the light guiding plate  26 . The plurality of diffusion lens elements  26   s   2  are provided in two rows, namely upper and lower rows as best seen in  FIG. 2 , and each diffusion lens element  26   s   2  is formed as a fisheye lens. As a result, the light that has reached the front end surface  26   b  of the light guiding plate  26  is emitted to the front of the lamp as light that diffuses in the vertical and lateral directions about the optical axis Ax. 
       FIG. 6(   a ) is a front view showing how the light guiding plate unit  16  appears when each light-emitting element  22  is lit in the vehicular lamp  10  according to the shown embodiment.  FIG. 6  is a front view showing, as in the conventional example, how the light guiding plate unit  16 ′ appears when each light-emitting element  22  is lit in the case where no lens member unit  18  is provided in the configuration of the vehicular lamp  10  of the shown embodiment. 
     The light guiding plate unit  16 ′ shown in  FIG. 6(   b ) is similar to the light guiding plate unit  16  of the shown embodiment of the present invention in the shape of the front end surface  16   b ′; however, the rear end surface of the light guiding plate unit  16 ′ is constructed so that the rear end surface  26   a ′ of each light guiding plate  26 ′ allows the emitted light from the light-emitting element  22  to be incident on the light guiding plate  26  as light parallel to the optical axis Ax. 
     As shown in  FIG. 6(   a ), in the light guiding plate unit  16  of the shown embodiment, each of the respective central portions of the plurality of diffusion lens elements  26   s   2  formed on the front end surface  26   b  of each light guiding plate  26  appears to be lit as a bright portion B, and in this case, all of the plurality of diffusion lens elements  26   s   2  of each light guiding plate  26  appear to be brightly lit in a substantially uniform manner. 
     On the other hand, as shown in  FIG. 6(   b ), in the light guiding plate unit  16 ′ as well, each of the respective central portions of a plurality of diffusion lens elements  26   s   2 ′ formed on a front end surface  26   b ′ of each light guiding plate  26 ′ appears to be lit as a bright portion B′: However, the light guiding plate unit  16 ′ is generally darker than the light guiding plate unit  16  of the shown embodiment, and though the area close to the optical axis Ax in each light guiding plate  26 ′ is relatively bright, each light guiding plate  26 ′ becomes rapidly dark as the distance from the optical axis Ax increases to the left and right sides. This is because, the light guiding plate unit  16 ′, the emitted light from each light-emitting element  22  that reaches the rear end surface  26   a ′ of each light guiding plate  26 ′ has such an intensity distribution that the light intensity rapidly decreases as the distance from the optical axis Ax increases to the left and right sides, and the amount of emitted light from each light-emitting element  22  that reaches the rear end surface  26   a ′ of each light guiding plate  26 ′ is small. 
     Effects Of the shown embodiment of the present invention will be described below. 
     The vehicular lamp  10  according to the shown embodiment is constructed so that the emitted light from the light-emitting element  22  is incident on the rear end surface  26   a  of the light guiding plate  26  and then is emitted out from the front end surface  26   b  of the light guiding plate  26  to the front of the lamp, and in this structure, the lens member  28  is provided between the light-emitting element  22  and the light guiding plate  26 , and the lens member  28  allows a part of the emitted light from the light-emitting element  22 , which travels in a direction close to the optical axis Ax (i.e., a direction close to the forward direction of the light-emitting element  22 ), to reach the light guiding plate  26  as diffusing light that diffuses in a horizontal plane (i.e., in a first plane along the light guiding plate  26 ), and further allows the emitted light from the light-emitting element  22  to reach the light guiding plate  26  as parallel light along the optical axis Ax (i.e., as converging light that converges in the forward direction of the light-emitting element  22 ) in a vertical plane (i.e., in a second plane orthogonal to the first plane). Accordingly, the following effects can be obtained. 
     Since the lens member  28  allows a part of the emitted light from the light-emitting element  22 , which travels in the direction close to the optical axis Ax, to reach the light guiding plate  26  as diffusing light that diffuses in the horizontal plane, the light that reaches the light guiding plate  26  is prevented from having such an intensity distribution that the light intensity becomes extremely high in the forward direction of the light-emitting element  22  in the horizontal plane. Accordingly, the light guiding plate  26  appears to be lit in a substantially uniform manner in the horizontal direction when the light guiding plate  26  is observed from the front of the lamp. 
     Moreover, the lens member  28  allows the emitted light from the light-emitting element  22  to reach the light guiding plate  26  as parallel light along the optical axis Ax in the vertical plane. Accordingly, the emitted light from the light-emitting element  22  can be efficiently incident on the light guiding plate  26 , and thus the light guiding plate  26  appears to be brightly lit when the light guiding plate  26  is observed from the front of the lamp. 
     As seen from the above, according to the shown embodiment of the present invention, the light guiding plate  26  in the vehicular lamp  10  is allowed to appear to be brightly lit in a substantially uniform manner, and this can improve the appearance of the lamp. 
     Furthermore, in the shown embodiment, the lens member  28  causes the emitted light from the light-emitting element  22  to reach the light guiding plate  26  in a luminance distribution that a pair of luminance peak values appear on both left and right sides of the optical axis Ax in the horizontal plane. Accordingly, the light that reaches the light guiding plate  26  has a more uniform luminance intensity distribution in the horizontal plane, thus allowing the light guiding plate  26  to appear to be more uniformly lit in the horizontal direction when the light guiding plate  26  is observed from the front of the lamp. 
     Moreover, in the shown embodiment, the lens component  26   s   1  is formed on the rear end surface  26   a  of the light guiding plate  26 , and the lens component  26   s   1  allows the emitted light: from the light-emitting element  22 , which has reached the light guiding plate  26  through the lens member  28 , to be incident on the light guiding plate  26  as parallel light along the optical axis Ax (i.e., as converging light that converges in the forward direction of the light-emitting element  22 ) in the horizontal plane. Accordingly, the light guiding plate  26  can be easily made to appear to be brightly lit in a substantially uniform manner in the horizontal direction when the light guiding plate  26  is observed from the front of the lamp. 
     In the shown embodiment, the light-emitting element  22  is provided at three positions in the horizontal plane, and each of the lens member  28  and the light guiding plate  26  is provided at three positions corresponding to the three light-emitting elements  22 . Furthermore, the three lens members  28  are coupled together to form the single lens member unit  18 , and the three light guiding plates  26  are coupled together to form the single light guiding plate unit  16 . Accordingly, the light guiding plates  26  provided at the three positions appear to be brightly lit in a substantially uniform manner in the horizontal direction when the light guiding plate unit  16  is observed from the front of the lamp, and this can be implemented with a smaller number of parts. 
     In the description of the above embodiment, the lens component  26   s   1  formed on the rear end surface  26   a  of the light guiding plate  26  is a Fresnel lens having a vertical ridge and groove pattern. However, the lens component  26   s   1  can be formed by a cylindrical lens extending in the vertical direction, etc. 
     In the description of the above embodiment, each of the light-emitting element  22 , the light guiding plate  26 , and the lens member  28  is provided at three positions. However, it should be understood that each of the light-emitting element  22 , the light guiding plate  26 , and the lens member  28  can be placed at two or less positions or at four or more positions. 
     In the description of the above embodiment, the vehicular lamp  10  is a front turn signal lamp mounted at the left front end of the vehicle. However, even if the vehicular lamp  10  is a front turn signal lamp mounted at the right front end of the vehicle or is a lamp other than the front turn signal lamp, such as, e.g., a tail lamp, effects similar to those of the above embodiment can be obtained by using a configuration similar to that of the above embodiment. 
     A modification of the above embodiment will be described below. 
       FIG. 7  is a view similar to  FIG. 1 , and it shows a vehicular lamp  110  according to the modification of the above-described embodiment. 
     As shown in  FIG. 7 , the vehicular lamp  110  according to this modification is similar to the above-described embodiment in terms of the basic configuration, but is partially different therefrom in the configurations of the lamp body  112 , the translucent cover  114 , and the light guiding plate unit  116 . 
     More specifically, the translucent cover  114  of the modification is formed to extend for a larger extent toward the rear side of the lamp than the translucent cover  14  of the above-described embodiment. Accordingly, the lamp body  112  of the modification is slightly different from the lamp body  12  of the above-described embodiment in the shape of the front end opening of the lamp body  112 . 
     The light guiding plate unit  116  of the modification is formed so that a front end surface  116   b  thereof extends to a large extent toward the rear side of the lamp from the right end to the left end thereof so as to correspond to the wrap-around shape of the translucent cover  114 . 
     The light guiding plate unit  116  is formed so that the rear end surfaces  126   a  of the light guiding plates  126  provided at three positions face a direction inclined to the left side With respect to the forward direction of the lamp. In other words, in this modification as well, though a Fresnel lens having a vertical ridge and groove pattern is formed as a lens component  126   s   1  on the rear end surface  126   a  of each light guiding plate  126 , its reference axis Ax 1  s inclined to the left side with respect to the optical axis Ax. In this case, the inclination angle θ at which each reference axis Ax 1  is inclined to the left Side with respect to the optical axis Ax is set to be gradually increased in the order of the light guiding plate  126  located on the right side, the light guiding plate  126  located in the middle, and the light guiding plate  126  located on the left side. 
       FIG. 8(   a ) is a detailed view of the portion  8 ( a ) in  FIG. 7 .  FIG. 8(   b ) is a view similar to  FIG. 8(   a ), and it shows a comparative example. 
     The light guiding plate unit  116 ′ shown in  FIG. 8(   b ) is similar to the light guiding plate unit  116  of the modification of  FIG. 7  in terms of the shape of the front end surface  116   b ′ of the light guiding plate unit  116 ′. However, regarding the rear end surface  126   a ′ of each light guiding plate  126 ′ of the light guiding plate unit  116 ′ faces the forward direction of the lamp, as in the light guiding plate unit  16  of the above-described embodiment. 
     As shown in  FIG. 8(   a ), in the light guiding plate unit  116  of this modification, the rear end surface  126   a  of each light gliding plate  126  faces the direction inclined to the left side. Accordingly, the emitted light from each light guiding plate  126  is emitted as diffusing light that diffuses in a balanced manner to both left and right sides with respect to the forward direction of the lamp, even though a plurality of lens elements  126   s   2  are continuously formed on the front end surface  126   b  of each light guiding plate  126  along the wrap-around shape of the front end surface  126   b.    
     On the other hand, as shown in  FIG. 8(   b ), in the light guiding plate unit  116 ′ of the comparative example, the rear end surface  126   a ′ of each light guiding plate  126 ′ faces the forward direction of the lamp, and a plurality of lens elements  126   s   2 ′ are continuously formed on the front end surface  126   b ′ of each light guiding plate  126 ′ along the wrap-around shape of the front end surface  126   b ′. Accordingly, the emitted light from each light guiding plate  126 ? diffuses in a direction toward the right side with respect to the forward direction of the lamp, and apart of the light that has reached the front end surface  126   b ′ of each light guiding plate  126 ′ is totally reflected by the lens elements  126   s   2 ′. Thus, the emitted light from each light guiding plate  126 ′ cannot be emitted as diffusing light that diffuses in a balanced manner to both left and right sides with respect to the forward direction of the lamp, causing loss of the amount of the emitted light. 
     In this case, as shown by two-dotted broken lines in  FIG. 8(   b ), if a plurality of lens elements  126   s   3 ′ facing the forward direction of the lamp are formed in a staircase pattern on the front end surface  126   b ′ of each light guiding plate  126 ′, the emitted light from each light guiding plate  126 ′ can be diffused in a balanced manner to both left and right sides with respect to the forward direction of the lamp, and also loss of the amount of emitted light can be eliminated. However, this configuration may degrade the appearance of the light guiding plate unit  116 ′ due to the large steps formed between the plurality of lens elements  126   s   3 ′. 
     On the other hand, by using the configuration of the modification of  FIG. 7 , effects similar to those of the above-described embodiment can be obtained without degrading the appearance of the light guiding plate unit  116 , even if the front end surface  116   b  of the light guiding plate unit  116  is formed to extend to a large extent toward the rear side of the lamp from the right end to the left end thereof. 
     In particular, in the light guiding plate unit  116  of the modification, the inclination angle θ at which the reference axis Ax 1  of the rear end surface  126   a  of each light guiding plate  126  is inclined to the left side with respect to the optical axis Ax is set to gradually increase in the order of the right side, the middle, and the left side, according to the degree of wrap-around of the front end surface  116   b . Accordingly, the emitted light from each light, guiding plate  126  diffuses in a more balanced manner to both left and right sides with respect to the forward direction of the lamp, even though the plurality of lens elements  126   s   2  are continuously formed on the front end surface  126   b  of each light guiding plate  126 . 
     It should be understood that the numerical values shown as specification in the above embodiment and the modification are by way of example only, and can be set to be appropriate different values.