Abstract:
A vehicle lamp includes a light source mounted on a vehicle body and a light guide body for guiding light generated by the light source. On the light guide body, vertically to a light travelling direction, a plurality of notch-shaped portions are formed in line. The notch-shaped portions become narrow in pitch as the distance from the light source increases and are formed deeper as the distance from the light source increases. Preferably, the notch-shaped portions exhibit arc cross-sections having the same curvature radius, and the depths of the notch-shaped portions are specified by the central angles of the arc cross-sections.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an improved vehicle lamp. 
       BACKGROUND ART 
       [0002]    Among the conventionally-known techniques related to lamps mounted on vehicles (i.e., vehicle lamps) is one disclosed in Patent Literature 1. 
         [0003]    The vehicle lamp disclosed in Patent Literature 1 is for use as a blinker lamp of an automotive vehicle and includes a light source, and a light guide member for guiding light emitted by the light source. The light guide member has a plurality of recess-shaped portions formed therein perpendicularly to a traveling direction of light. Pitches between the recess-shaped portions progressively narrow or decrease as distances, from the light source, of the recess-shaped portions increase, i.e., with the increasing distance from the light source. 
         [0004]    Light within the light guide member reflects toward outside at positions where the recess-shaped portions are formed. Energy of the light is great in the neighborhood of the light source, and thus, sufficient light can be secured with a small number of the recess-shaped portions formed in that neighborhood. The light energy decreases with the increasing distance from the light source. 
         [0005]    Therefore, in such a distant area, a greater number of recess-shaped portions are formed so that more light can be reflected and thus necessary light can be secured. With the vehicle lamp constructed as above, the entire light guide member can be illuminated uniformly. 
         [0006]    Such a vehicle lamp has a function of allowing a person (or persons) outside the vehicle to recognize the vehicle. In order to allow a person outside the vehicle to recognize the vehicle, it is desirable that the light guide member can be illuminated uniformly and in various illumination styles. 
       PRIOR ART LITERATURE 
     Patent Literature 
       [0007]    Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2005-2667928 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    It is therefore an object to provide a technique which can freely control a degree of brightness (brightness and darkness) of light emitted from a vehicle lamp. 
       Solution to Problem 
       [0009]    According to one aspect of the present invention, there is provided an improved vehicle lamp including a light source mounted on a vehicle body, and a light guide member for guiding light emitted by the light source, characterized in that the light guide member has a row of a plurality of recess-shaped portions formed therein substantially perpendicularly to a traveling direction of the light emitted by the light source, and the recess-shaped portions are formed in such a manner that, as distances, from the light source, of individual ones of the recess-shaped portions increase, pitches between the recess-shaped portions decrease and depths of the recess-shaped portions increase. 
         [0010]    Preferably, the plurality of recess-shaped portions each have an arcuate section of a same radius of curvature, and the depth of each of the recess-shaped portions is defined by a central angle of the arcuate section. 
         [0011]    Preferably, each of the recess-shaped portions comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the opposed surfaces extend from one point gradually away from each other, and, as viewed perpendicularly to a surface where the recess-shaped portions are formed, respective edges of the pair of opposed surfaces form a line corresponding to a part of a halved parabola. 
         [0012]    Preferably, each of the recess-shaped portions comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the opposed surfaces extend from one point gradually away from each other, and, as viewed perpendicularly to a surface where the recess-shaped portions are formed, respective edges of the pair of opposed surfaces form a line corresponding to at least a part of a line of an ellipse divided into one-fourth along long and short axes thereof. 
         [0013]    Preferably, as viewed in a section taken along an arranged direction of the plurality of recess-shaped portions, portions between the recess-shaped portions are each formed straight or substantially straight such that the light does not leak to outside of the light guide member. 
         [0014]    Preferably, the depths of the recess-shaped portions are set within a range of 0.01 μm to 25.00 μm, and the pitches between the recess-shaped portions are set equal to or greater than a lower limit value of 0.1 mm. 
       Advantageous Effects of Invention 
       [0015]    According to the present invention, the recess-shaped portions are formed in such a manner that, as the distances, from the light source, of the individual recess-shaped portions increase, the pitches between the recess-shaped portions decrease and the depths of the recess-shaped portions increase. The light in the interior of the light guide member reflects toward outside at positions where the recess-shaped portions are formed. Because the light energy is great in the neighborhood of the light source, sufficient brightness can be secured by only a small number of the recess-shaped portions formed with small or shallow depths in that neighborhood. On the other hand, the light energy decreases with the increasing distance from the light source. In such a portion distant from the light source, a greater number of the recess-shaped portions are formed with greater or deeper depths. With the aforementioned arrangements, it is possible to secure necessary brightness. By adjusting the pitches and depths of the recess-shaped portions, it is possible to lightly illuminate a portion of the light guide member most distant from the light source and lightly illuminate a longitudinal middle portion of the light guide member. Thus, the present invention can freely control a degree of brightness (brightness and darkness) of light and enhance outer appearance quality. 
         [0016]    Further, according to the present invention, the plurality of recess-shaped portions each have an arcuate section. If each of the recess-shaped portions is shaped to have a straight section, the light tends to reflect in similar directions. As a consequence, the vehicle lamp looks bright or dark depending on the angle it is viewed at from the outside. By contrast, in the present invention, each of the recess-shaped portions has an arcuate section, so that the light reflects in various directions. In this way, the vehicle lamp can be illuminated with substantially uniform brightness irrespective of the angle it is viewed at from the outside. Thus, the vehicle lamp can have a high visibility from the outside. 
         [0017]    Further, according to the present invention, the respective edges of the pair of opposed surfaces of the recess-shaped portion form a line corresponding to a part of a halved parabola. If the recess-shaped portion is shaped to have a straight section, the light tends to reflect in similar directions. As a consequence, the vehicle lamp looks bright or dark depending on the angle it is viewed at from the outside. By contrast, in the present invention, each of the recess-shaped portions has an arcuate section, so that the light reflects in various directions. In this way, the vehicle lamp can be illuminated with substantially uniform brightness irrespective of the angle it is viewed at from the outside. Thus, the vehicle lamp can have a high visibility from the outside. 
         [0018]    Further, according to the present invention, the respective edges of the pair of opposed surfaces of the recess-shaped portion form a line corresponding to a part of a halved parabola. If the recess-shaped portion is shaped to have a straight section, the light tends to reflect in similar directions. As a consequence, the vehicle lamp looks bright or dark depending on the angle it is viewed at from the outside. By contrast, in the present invention, each of the recess-shaped portions has an arcuate section, so that the light reflects in various directions. In this way, the vehicle lamp can be illuminated with substantially uniform brightness irrespective of the angle it is viewed at from the outside. Thus, the vehicle lamp can have a high visibility from the outside. 
         [0019]    Further, according to the present invention, the respective edges of the pair of opposed surfaces of the recess-shaped portion form a line corresponding to at least a part of a line of an ellipse divided into one-fourth along long and short axes thereof. If the recess-shaped portion is shaped to have a straight section, the light tends to reflect in similar directions. As a consequence, the vehicle lamp looks bright or dark depending on the angle it is viewed at from the outside. By contrast, in the present invention, each of the recess-shaped portions has an arcuate section, so that the light reflects in various directions. In this way, the vehicle lamp can be illuminated with substantially uniform brightness irrespective of the angle it is viewed at from the outside. Thus, the vehicle lamp can have a high visibility from the outside. 
         [0020]    Furthermore, according to the present invention, as viewed in a section taken along the arranged direction of the plurality of recess-shaped portions, the portions between the recess-shaped portions are each formed straight or substantially straight such that the light does not leak to outside of the light guide member. In the surface portions formed straight or substantially straight, the light does not reflect toward outside of the light guide member. In this way, it is possible to reduce light energy loss occurring between the recess-shaped portions and thereby finely control the degree of brightness (brightness and darkness) of the light. 
         [0021]    Furthermore, according to the present invention, the depths of the recess-shaped portions are set within the range of 0.01 μm to 25.00 μm, and the pitches between the recess-shaped portions are set equal to or greater than the lower limit value of 0.1 mm. It has been found that the outer appearance quality of the light guide member when the light source is OFF or in a non-illuminated state has a tendency of degrading as the recess-shaped portion depth increases above 25.00 μm. It is considered that such degrading of the outer appearance quality is due to the fact that the recess-shaped portion appears as a line because it is deep. Therefore, it is preferable that the depth of the recess-shaped portion be 0.01 μm or more but 25.00 μm or less. 
         [0022]    It has also been found that, if the pitch between the recess-shaped portions is 0.01 mm or less, the outer appearance quality of the light guide member when the light source is in the non-illuminated state has a tendency of degrading. It is considered that such degrading of the outer appearance quality is due to the fact that, even where the recess-shaped portions are shallow or small in depth, the light guide member becomes undesirably cloudy because the recess-shaped portions are located too close to each other. Therefore, it is preferable the pitch between the recess-shaped portions be 0.10 mm or more. 
         [0023]    Because the depths of the recess-shaped portions are set within a range of 0.01 μm to 25.00 μm and the pitches between the recess-shaped portions are set equal to or greater than the lower limit value of 0.1 mm, the present invention can improve the outer appearance quality of the light guide member when the light source is in the non-illuminated state. Namely, the present invention can provide a vehicle lamp presenting a high outer appearance quality both when the light source is in the illuminated state and when the light source is in the non-illuminated state. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1  is a perspective view of a vehicle on which is mounted a first embodiment of a vehicle lamp of the present invention; 
           [0025]      FIG. 2  is a perspective view of the position lamp shown in  FIG. 1 ; 
           [0026]      FIG. 3  is a sectional view taken along the  3 - 3  line of  FIG. 2 ; 
           [0027]      FIG. 4  is an enlarged view of sections depicted at  4 ( a ) to  4 ( c ) in  FIG. 3 ; 
           [0028]      FIG. 5  is a graph showing relationship between formed positions of the individual recess-shaped portions and depths of the recess-shaped portions; 
           [0029]      FIG. 6  is a view explanatory of operation of the recess-shaped portions shown in  FIG. 3 ; 
           [0030]      FIG. 7  is a view showing a test piece of a light guide member that was used in experiments conducted for depths and pitches of the recess-shaped portions shown in  FIG. 3 ; 
           [0031]      FIG. 8  is a graph explanatory of a modification of the relationship between the formed positions of the individual recess-shaped portions and the depths of the recess-shaped portions shown in  FIG. 5 ; 
           [0032]      FIG. 9  is a view explanatory of a modification of the recess-shaped portion shown in  FIG. 6 ; 
           [0033]      FIG. 10  is an enlarged view showing recess-shaped portions employed in a second embodiment of the vehicle lamp of the present invention; and 
           [0034]      FIG. 11  is an enlarged view showing recess-shaped portions employed in a third embodiment of the vehicle lamp of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0035]    Now, embodiments of the present invention will be described, with reference to the accompanying drawings, in relation to a case where a vehicle lamp of the invention is applied as a position lamp for a vehicle. 
       Embodiment 1 
       [0036]    As shown in  FIG. 1 , a headlight unit  20  is mounted on a front section of a vehicle body  11  constituting a frame of the vehicle  10 . The headlight unit  20  includes: a high beam bulb  21  for illuminating an area in front of the vehicle  10 ; a lower beam bulb  22  for illuminating an area forward and downward of the vehicle  10 ; and a position lamp  30  (vehicle lamp  30 ) provided to surround the high beam bulb  21  and the lower beam bulb  22 . 
         [0037]    The position lamp  30  is provided to allow a person(s) outside the vehicle to readily recognize the vehicle  10 . With reference to  FIG. 2  and subsequent figures, a detailed description will be given about the position lamp  30 . 
         [0038]    As shown in  FIG. 2 , the position lamp  30  includes: a housing  31 ; a light source  32  in the form of an LED accommodated in the housing  31 ; and a light guide member  33  of a generally Y shape provided adjacent to the light source  32 . 
         [0039]    The light guide member  33 , which is formed for example of acryl, slightly curves as a whole along the contour of a part of the vehicle body  11 . The light guide member  33  has a plurality of recess-shaped portions  33   a  to  33   l  formed therein perpendicularly to a traveling direction of light emitted by the light source  32 . The recess-shaped portions  33   a  to  33   l  differ from one another in depth. 
         [0040]    In the present invention, positions where the recess-shaped portions  33   a  to  33   l  (formed positions of the recess-shaped portions  33   a  to  33   l ) and respective depths of the recess-shaped portions  33   a  to  33   l  are particularly important. The recess-shaped portions  33   a  to  33   f  and the recess-shaped portions  33   g  to  33   l  are based on the same technical idea of the invention, and thus, the following describe in detail the recess-shaped portions  33   a  to  33   f  with a detailed description about the recess-shaped portions  33   g  to  33   l  omitted to avoid unnecessary duplication. 
         [0041]    The recess-shaped portions  33   a  to  33   l  only need be of a notch shape. Namely, the recess-shaped portions  33   a  to  33   l  need not necessarily be formed by recessing. The light guide member  33  and the recess-shaped portions  33   a  to  33   f  will be detailed hereinbelow with reference to  FIG. 3  and subsequent figures. 
         [0042]    As shown in  FIG. 3 , the recess-shaped portions  33   a  to  33   f  are formed in a back surface section Re of the light guide member  33 . A front surface section Fr and side surface sections Si of the light guide member  33  are formed as flat surfaces. Upper and lower surface sections of the light guide member  33  are also formed as flat surfaces. 
         [0043]    Lengths between the individual recess-shaped portions  33   a  to  33   f  will be referred to as pitches. The pitches P 1  to P 5  narrow or decrease as distances, from the light source  32 , of the recess-shaped portions  33   a  to  33   f  increase; that is, the pitches P 1  to P 5  decrease with the increasing distance from the light source  32 . Further, respective depths D 1  to D 6  of the recess-shaped portions  33   a  to  33   f  increase as the distances, from the light source  32 , of the recess-shaped portions  33   a  to  33   f  increase; that is, the recess-shaped portions  33   a  to  33   f  are formed deeper with the increasing distance from the light source  32 . The pitches P 1  to P 5  between the recess-shaped portions  33   a  to  33   f  are measured by measuring distances between the respective deepest parts of the recess-shaped portions  33   a  to  33   f.    
         [0044]    A back surface portion between the recess-shaped portion  33   a  and the recess-shaped portion  33   b  is formed straight (i.e., as a straight surface) in the illustrated example of  FIG. 3 . Actually, however, because the light guide member  33  extends along the contour of a part of the vehicle body  11  ( FIG. 1 ), the back surface portion between the recess-shaped portion  33   a  and the recess-shaped portion  33   b  slightly curves. Curvature of the back surface portion between the recess-shaped portion  33   a  and the recess-shaped portion  33   b  is set such that the light traveling within the light guide member  33  does not leak to outside of the light guide member  33 . Back surface portions between the other recess-shaped portions are formed in a similar manner to the back surface portion between the recess-shaped portion  33   a  and the recess-shaped portion  33   b.  Namely, the back surface portions between the recess-shaped portions  33   a  to  33   e  and the recess-shaped portions  33   b  to  33   f  are formed substantially straight such that the light traveling within the light guide member  33  does not leak to outside of the light guide member  33 . 
         [0045]      FIG. 4( a )  shows in enlarged scale a section encircled at  4   a  in  FIG. 3 . Similarly,  FIG. 4( b )  shows in enlarged scale a section encircled at  4   b  in  FIG. 3 , and  FIG. 4( c )  shows in enlarged scale a section encircled at  4   c  in  FIG. 3 . 
         [0046]    As shown in  FIG. 4( a ) , the recess-shaped portion  33   a  is shaped such that arcuate back surfaces, each having a radius y and a central angle θ 1 , are opposed to each other. Namely, the recess-shaped portion  33   a  comprises two arcuate back surfaces opposed to each other and these opposed arcuate back surfaces have the same radius and same central angle. The other recess-shaped portions  33   b  to  33   l  are shaped substantially similarly to the recess-shaped portion  33   a.    
         [0047]    As shown in  FIG. 4( b ) , the recess-shaped portion  33   d  is shaped such that arcuate back surfaces, each having a radius γ and a central angle θ 4 , are opposed to each other. Further, as shown in  FIG. 4( c ) , the recess-shaped portion  33   f  is shaped such that arcuate back surfaces, each having a radius γ and a central angle θ 6 , are opposed to each other. The central angle θ 6  is 90° that is the greatest angle the central angle θ can take. 
         [0048]    As seen in  FIGS. 4( a ) to 4( c ) , the depths D 1 , D 4  and D 6  of the recess-shaped portions  33   a,    33   d  and  33   f  are in relationship of D 1 &lt;D 4 &lt;D 6 , and the center angles θ 1 , θ 4  and θ 6  of the recess-shaped portions  33   a,    33   d  and  33   f  are in relationship of 0°&lt;θ≦90° and θ 1 &lt;θ 4 &lt;θ 6 . 
         [0049]    Referring also to  FIG. 3 , the plurality of recess-shaped portions  33   a  to  33   f  each have an arcuate section of the same radius of curvature γ, and the depths D 1  to D 6  of the recess-shaped portions  33   a  to  33   f  are defined or determined by the center angles θ of the arcuate sections of the recess-shaped portions  33   a  to  33   f.    
         [0050]      FIG. 5  shows relationship between the distances, from the light source, of the individual recess-shaped portions  33   a  to  33   f  and the depths of the recess-shaped portions  33   a  to  33   f.  Namely, in  FIG. 5 , the distances, from the light source, of the individual recess-shaped portions  33   a  to  33   f  are plotted on the horizontal axis, and the depths of the recess-shaped portions  33   a  to  33   f  are plotted on the vertical axis. 
         [0051]    Referring also to  FIG. 3 , in the case where the distances, from the light source, of the individual recess-shaped portions  33   a  to  33   f  and the depths of the recess-shaped portions  33   a  to  33   f  are in the relationship shown in  FIG. 5 , the position lamp  30  shown in  FIG. 3  is illuminated with the greatest brightness at a portion distant from the light source  32 , i.e. in the neighborhood of the recess-shaped portion  33   f.    
         [0052]    The way to illuminate the position lamp  30  can be changed by changing inclinations of a graph curve shown in  FIG. 5 , under condition that the pitches P 1  to P 5  are set to narrow or decrease and the depths D 1  to D 6  are set to increase as the distances, from the light source, of the individual recess-shaped portions  33   a  to  33   f  increase; namely, P 1 &gt;P 2 &gt;P 3 &gt;P 4 &gt;P 5 , and D 1 &lt;D 2 &lt;D 3 &lt;D 4 &lt;D 5 &lt;D 6 . 
         [0053]    Namely, the light in the interior of the light guide member  33  reflects toward the outside (depicted at Fr in  FIG. 3 ) of the light guide member  33  at positions where the recess-shaped portions  33   a  to  33   f  are formed. Because the light energy is great in the neighborhood of the light source  32 , sufficient brightness can be secured in the neighborhood of the light source  32  with a small number of the recess-shaped portions (e.g., the recess-shaped portion  33   a ) formed into a small or shallow depth in the neighborhood. 
         [0054]    On the other hand, the light energy decreases with the increasing distance from the light source  32 . In such a portion distant from the light source  32 , a greater number of the recess-shaped portions (e.g., the recess-shaped portions  33   e  and  33   f ) are formed with greater or deeper depths. 
         [0055]    With the aforementioned arrangements, it is possible to secure necessary brightness. By adjusting the pitches P 1  to P 5  and depths D 1  to D 6  of the recess-shaped portions  33   a  to  33   f,  it is possible to lightly illuminate a portion of the light guide member  33  most distant from the light source  32 . Further, it is possible to lightly illuminate a longitudinal middle portion of the light guide member  33 . In this way, it is possible to freely control a degree of brightness (brightness and darkness) of the light and enhance an outer appearance of the vehicle lamp. 
         [0056]    In a comparative example shown in  FIG. 6( a ) , a recess-shaped portion  133  is shaped to have straight surfaces. Because of the straight surfaces, light tends to reflect from the recess-shaped portion  133  in fixed, similar directions as indicated by arrows; the light can easily reflect in some directions but is difficult to reflect in the other directions. As a consequence, the position lamp  130  looks bright or dark depending on the angle it is viewed at from the outside. 
         [0057]    As shown in  FIG. 6( b ) , each of the recess-shaped portions  33   a  to  33   f  in the instant embodiment of the invention, on the other hand, has arcuate sections, so that the light reflects in various directions as indicated by arrows. In this way, the position lamp  30  can be illuminated with substantially uniform brightness irrespective of the angle it is viewed at from the outside. Thus, the position lamp  30  can have a high visibility from the outside. 
         [0058]    Referring also to  FIG. 3 , the surface portions between the recess-shaped portions  33   a  to  33   e  and the surface portions between the recess-shaped portions  33   b  to  33   f  are formed straight as viewed in section or formed substantially straight as viewed in section such that the light does not leak to outside of the light guide member  33 . In the surface portions formed straight or substantially straight, the light does not reflect toward outside of the light guide member  33 . In this way, it is possible to reduce light energy loss occurring between the recess-shaped portions  33   a  to  33   f  and thereby finely control the degree of brightness (brightness and darkness) of the light. 
         [0059]    The inventors of the present invention etc. found that the degree of brightness (brightness and darkness) of the light can be freely controlled and the outer appearance of the vehicle lamp  30  by adjusting the depths and pitches of the recess-shaped portions. The light guide member is a component part that is visible from outside of the vehicle when the light source is OFF (i.e., in a non-illuminated state), such as during daytime. It was also found that, if the depths of the recess-shaped portions are too deep and the pitches between the recess-shaped portions are too short, the recess-shaped portions would undesirably appear as lines and the light guide member would undesirably appear cloudy. If the light guide member appears cloudy like this, the outer appearance of the light guide member and hence the vehicle lamp would be impaired. For these reasons, the inventors of the present invention etc. conducted the following experiments with a view to providing an improved vehicle lamp that can have an improved outer appearance quality even when the light source is OFF or in the non-illuminated state. 
         [0060]      FIG. 7  shows a test piece  43  of the light guide member that was used in the experiments. The test piece  43  has recess-shaped portions  43   a,  each having a depth (recess-shaped portion depth) of a (μm), formed therein with a pitch of b (mm). Namely, in the one test piece  43 , the recess-shaped portions  43   a  have the same depth (recess-shaped portion depth) a (μm) and the same pitch b (mm). 
         [0061]    The experiments were carried out using a plurality of test pieces  43  made with the depth a (μm) and pitch b (mm) differentiated among the test pieces  43 . More specifically, the experiments were carried out by measuring Haze values of the individual test pieces  43 . If the Haze value is less 50, the light guide member is judged or determined acceptable because it is not cloudy or, if cloudy, it does not substantively influence the outer appearance of the light guide member. If the haze value is 50 or more, on the other hand, the light guide member is determined unacceptable because it substantively influences the outer appearance of the light guide member. Results of the experiments are shown below. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 b pitch (mm) 
               
             
          
           
               
                   
                 0.01 
                 0.05 
                 0.10 
                 0.20 
                 0.30 
                 0.50 
               
               
                   
                   
               
             
          
           
               
                 a 
                 0.01 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 recess-shaped 
                 1.00 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 portion 
                 5.00 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 depth 
                 10.00 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                 (μm) 
                 20.00 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                 25.00 
                 X 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                 30.00 
                 X 
                 X 
                 X 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
               
             
          
         
       
     
         [0062]    As shown in TABLE 1 above, in the case where the recess-shaped portion depth was 0.01 (μm) and the pitch was 0.01 (mm), the Haze value was less than 5.0. In these conditions, the light guide member presented a high outer appearance quality and was determined acceptable (◯). 
         [0063]    Similarly, in the case where the recess-shaped portion depth was 0.01 (μm) and the pitch was 0.05, 0.10, 0.20, 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0064]    Further, in the case where the recess-shaped portion depth was 1.0 (μm) and the pitch was 0.01, 0.05, 0.10, 0.20. 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0065]    Further, in the case where the recess-shaped portion depth was 5.00 (μm) and the pitch was 0.1 (mm), the Haze value was 5.0 or more. In these conditions, the light guide member was cloudy and determined unacceptable (×). 
         [0066]    On the other hand, in the case where the recess-shaped portion depth was 5.0 (μm) and the pitch was 0.05, 0.10, 0.20. 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0067]    Further, in the case where the recess-shaped portion depth was 10.00 (μm) and the pitch was 0.01 (mm), the light guide member was determined unacceptable (×). 
         [0068]    On the other hand, in the case where the recess-shaped portion depth was 10.00 (μm) and the pitch was 0.05, 0.10, 0.20, 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0069]    Further, in the case where the recess-shaped portion depth was 20.00 (μm) and the pitch was 0.01 (mm), the light guide member was determined unacceptable (×). 
         [0070]    On the other hand, in the case where the recess-shaped portion depth was 20.00 (μm) and the pitch was 0.05, 0.10, 0.20, 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0071]    Furthermore, in the case where the recess-shaped portion depth was 25.00 (μm) and the pitch was 0.01 or 0.05 (mm), the light guide member was determined unacceptable (×). 
         [0072]    On the other hand, in the case where the recess-shaped portion depth was 25.00 (μm) and the pitch was 0.10, 0.20, 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0073]    Furthermore, in the case where the recess-shaped portion depth was 30.00 (μm) and the pitch was 0.01, 0.05 or 0.10 (mm), the light guide member was determined unacceptable (×). 
         [0074]    On the other hand, in the case where the recess-shaped portion depth was 30.00 (μm) and the pitch was 0.20, 0.30 or 0.50 (mm), the light guide member was determined acceptable (◯). 
         [0075]    From the aforementioned results of the experiments, it was found that the outer appearance quality of the light guide member when the light source is in the non-illuminated state has a tendency of degrading as the recess-shaped portion depth increases above 25.00 μm. It is considered that such degrading of the outer appearance quality is due to the fact that the recess-shaped portion  43   a  appears as a line because it is deep. Therefore, it is preferable that the depth of the recess-shaped portion  43   a  be 0.01 μm or more but 25.00 μm or less. 
         [0076]    It was also found that, if the pitch between the recess-shaped portions  43   a  is 0.01 mm or less, the outer appearance quality of the light guide member when the light source is in the non-illuminated state has a tendency of degrading. It is considered that such degrading of the outer appearance quality is due to the fact that, even where the recess-shaped portions  43   a  are relatively shallow in depth, the light guide member becomes cloudy because the recess-shaped portions  43   a  are located too close to each other. Therefore, it is preferable the pitch between the recess-shaped portions  43   a  be 0.10 mm or more. 
         [0077]    Although the experiments were conducted only up to the pitch of 0.5 mm, it is considered, for the foregoing reasons, that the outer appearance quality of the light guide member when the light source is in the non-illuminated state would not degrade even if the pitch between the recess-shaped portions is increased above 0.5 mm. Therefore, it is considered that a high outer appearance quality of the light guide member can be secured if 0.1 mm is set as a lower limit value of the pitch. 
         [0078]    The depths of the recess-shaped portions  43   a  are set within a range of 0.01 to 25.00 μm, and the pitches between the recess-shaped portions  43   a  are set to be equal to or greater than the lower limit value of 0.10 mm. In this way, it is possible to improve the outer appearance quality of the light guide member when the light source is in the non-illuminated state. Namely, it is possible to provide a vehicle lamp presenting a high outer appearance quality both when the light source is in the illuminated state and when the light source is in the non-illuminated state. 
         [0079]      FIG. 8  shows a modification of the relationship between the distances, from the light source, of the individual recess-shaped portions and the depths of the individual recess-shaped portions. In  FIG. 8 , the horizontal axis represents the distances from the light source, while the vertical axis represents the depths of the individual recess-shaped portions. 
         [0080]    A graph curve in the modification the relationship shown in  FIG. 8  is different in inclination from the graph curve shown in  FIG. 5 . With the curve inclination shown in  FIG. 8 , it is possible to change the way in which the position lamp ( 30  in  FIG. 3 ) is illuminated. More specifically, with the inclination shown in  FIG. 8 , the longitudinal middle portion of the light guide member  33  can be illuminated lightly. 
         [0081]    According to the modification too, the pitches P 11  to P 15  between the recess-shaped portions ( 33   a  to  33   f  in  FIG. 3 ) are set to narrow (decrease) and the depths D 11  to D 16  of the recess-shaped portions are set to increase as the distances, from the light source ( 32  in  FIG. 3 ), of the individual recess-shaped portions increase; namely, P 11 &gt;P 12 &gt;P 13 &gt;P 14 &gt;P 15 , and D 11 &lt;D 12 &lt;D 13 &lt;D 14 &lt;D 15 &lt;D 16 . 
         [0082]    By adjusting the pitches and depths of the recess-shaped portions, the entire position lamp can be illuminated uniformly, but also the degree of brightness (brightness and darkness) of the position lamp can be freely controlled. 
         [0083]    As shown in  FIG. 9 , the recess-shaped portion  33   m  comprises arcuate surfaces opposed to and spaced from each other as viewed in section. The bottoms, i.e. deepest parts, of the opposed arcuate surfaces are interconnected by a straight line portion. In the recess-shaped portion  33   m,  the middle of the straight line portion is a reference point of the pitch. Even with the recess-shaped portion  33   m  shaped like this, it is possible to achieve predetermined advantageous benefits of the present invention. 
       Embodiment 2 
       [0084]    The following describe, with reference to  FIG. 10 , a second embodiment of the present invention.  FIG. 10( a )  shows in enlarged scale primary sections of a light guide member employed in the second embodiment of the vehicle lamp of the present invention.  FIG. 10( b )  shows a modification of the light guide member employed in the second embodiment of the vehicle lamp of the present invention.  FIGS. 10( a ) and 10( b  )  each correspond to  FIG. 4( c ) . 
         [0085]    The second embodiment of the vehicle lamp  50 ,  60  is different from the first embodiment of the vehicle lamp ( 30  in  FIG. 2 ) in terms of the shapes of the recess-shaped portions ( 33   a  to  33   f  in  FIG. 4 ). The other basic structural features of the second embodiment of the vehicle lamp  50 ,  60  are similar to those of the first embodiment of the vehicle lamp. The same elements as in the first embodiment are depicted by the same reference characters as used for the first embodiment and will not be described in detail here to avoid unnecessary duplication. 
         [0086]    As shown in  FIG. 10( a ) , the recess-shaped portion  53   a  is formed perpendicularly to the traveling direction of the light emitted by the light source ( 32  in  FIG. 2 ). Namely, the recess-shaped portion  53   a  is formed from the back surface toward the front surface of the light guide member  53 . Further, as the light guide member  53  is viewed in plan, the recess-shaped portion  53   a  comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the two surfaces extend from one point gradually away from each other. As viewed in plan (i.e., as viewed in a direction perpendicular to the surface where the recess-shaped portion  53   a  is formed), the respective edges of the two surfaces (i.e., edge of the recess-shaped portion  53   a ) together form a line corresponding to a part of a halved parabola. 
         [0087]    The recess-shaped portion  63   a  shown in  FIG. 10( b  )  is substantially similar to the recess-shaped portion  53   a  shown in  FIG. 10( a ) . Namely, the recess-shaped portion  63   a  is formed perpendicularly to the traveling direction of light emitted by the light source. Namely, the recess-shaped portion  63   a  is formed from the back surface toward the front surface of the light guide member  63 . Further, as the light guide member  63  is viewed in plan, the recess-shaped portion  63   a  comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the two surfaces extend from one point gradually away from each other. As viewed in plan, the respective edges of the two surfaces form a line corresponding to a part of a halved parabola. 
         [0088]    With such recess-shaped portions  53   a  and  63   a  too, it is possible to achieve the predetermined advantageous benefits of the present invention. The recess-shaped portion  53   a  of a steeper arcuate shape is more preferable than the recess-shaped portion  63   a  because it can more effectively diffuse the light from the light source. 
       Embodiment 3 
       [0089]    The following describe, with reference to  FIG. 11 , a third embodiment of the present invention.  FIG. 11( a )  shows in enlarged scale primary sections of a light guide member employed in the third embodiment of the vehicle lamp of the present invention.  FIG. 11( b  )  shows a modification of the light guide member employed in the third embodiment of the vehicle lamp of the present invention.  FIGS. 11( a ) and 11( b  )  each correspond to  FIG. 4( c ) . 
         [0090]    The third embodiment of the vehicle lamp  70 ,  80  is different from the first embodiment of the vehicle lamp ( 30  in  FIG. 2 ) in terms of the shapes of the recess-shaped portions ( 33   a  to  33   f  in  FIG. 4 ). The other basic structural features of the third embodiment of the vehicle lamp  70 ,  80  are similar to those of the first embodiment of the vehicle lamp. The same elements as in the first embodiment are depicted by the same reference characters as used for the first embodiment and will not be described in detail here. 
         [0091]    As shown in  FIG. 11( a ) , the recess-shaped portion  73   a  is formed perpendicularly to the traveling direction of the light emitted by the light source ( 32  in  FIG. 2 ). Namely, the recess-shaped portion  73   a  is formed from in the direction the back surface toward the front surface of the light guide member  73 . The recess-shaped portion  73   a  comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the two surfaces extend from one point (i.e. deepest point of the recess) gradually away from each other. As viewed in plan (i.e., as viewed in the direction perpendicular to the surface where the recess-shaped portion  73   a  is formed), the respective edges of the two surfaces (i.e., edge of the recess-shaped portion  73   a ) form a line corresponding to at least a part of a line of an ellipse divided into one-fourth along its long and short axes. 
         [0092]    The recess-shaped portion  83   a  shown in  FIG. 11( b  )  is similar to the recess-shaped portion  73   a  shown in  FIG. 11( a ) . Namely, the recess-shaped portion  83   a  is formed perpendicularly to the traveling direction of light emitted by the light source. Namely, the recess-shaped portion  83   a  is formed from the back surface toward the front surface of the light guide member  83 . Namely, the recess-shaped portion  83   a  is formed from the back surface toward the front surface of the light guide member  83 . The recess-shaped portion  83   a  comprises a pair of opposed surfaces formed in a line-symmetric relation to each other such that the two surfaces extend from one point (i.e. deepest point of the recess) gradually away from each other. As viewed in plan, the respective edges of the two surfaces form a line corresponding to a part of a line of an ellipse divided into one-fourth along its long and short axes. 
         [0093]    With such recess-shaped portions  73   a  and  83   a  too, it is possible to achieve the predetermined advantageous benefits of the present invention. The recess-shaped portion  73   a  of a steeper arc shape is more preferable than the recess-shaped portion  83   a  because it can more effectively diffuse the light from the light source. 
         [0094]    Whereas the vehicle lamp of the present invention has been described above as a position lamp of a passenger vehicle, the basic principles of the present invention are also applicable to any other outdoor lamps or indoor lamps. Further, the vehicle lamp of the present invention may be mounted on motorcycles. Namely, the vehicle lamp of the present invention is not limited to the aforementioned constructions and applications as long as it is a lamp designed for use in vehicles. 
       INDUSTRIAL APPLICABILITY 
       [0095]    The vehicle lamp of the present invention is well suited for application as a position lamp for a passenger vehicle. 
       LIST OF REFERENCE SIGNS 
       [0096]      11  . . . vehicle body,  30  . . . position lamp (vehicle lamp),  50 ,  60 ,  70 ,  80  . . . vehicle lamp,  32  . . . light source,  33 ,  53 ,  63 ,  73 ,  83  . . . light guide member,  33   a  to  33   m,    53   a,    63   a,    73   a.    83   a  . . . recess-shaped portion