Abstract:
A surface light source apparatus including a point light source, a light guide plate which spreads light introduced from the point light source into a planar shape to output the light from a light outgoing plane, and a light blocking member which covers parts of the point light source and the light outgoing plane of the light guide plate. A gap shielding member is projected toward the light outgoing plane from a surface on a side facing the light outgoing plane of the light blocking member. At least a portion facing the light outgoing plane in the gap shielding member is made of a material having a light blocking property.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a surface light source apparatus. For example, the surface light source apparatus according to the present invention is used as a backlight for a liquid crystal display device. 
   2. Description of the Related Art 
     FIG. 1  shows an enlarged cross-sectional view, partially broken away, of schematic structure near a light source of a conventional surface light source apparatus. In a light source  12  used in a surface light source apparatus  11 , vertical and horizontal surfaces and a rear surface of a transparent resin  14  sealing a LED  13  are covered with a case  15  made of a white resin, and only a front face of the transparent resin  14  is exposed from the case  15 . The light source  12  is mounted on a flexible printed board  16 . The light source  12  is vertically inverted such that the flexible printed board  16  is faced up, and the front face of the light source  12  faces an end face (light incident plane  18 ) of a light guide plate  17 . A diffusing sheet  20  is disposed while facing a light outgoing plane  19  of the light guide plate  17 , and a reflector plate  21  is disposed while facing a back side of the light guide plate  17 . For example, Japanese Patent Application Laid-Open No. 2003-215584 discloses the surface light source apparatus having the above configuration. 
   In order to achieve a low profile of the light guide plate  17  or enhancement of light use efficiency, as shown in  FIG. 1 , a height of the front face of the transparent resin  14  in the light source  12  is equal to a thickness of the light guide plate  17 , and the light source  12  is disposed such that a center in a height direction of the transparent resin  14  coincides with a center in a thickness direction of the light guide plate  17 . Therefore, a gap is generated between the light outgoing plane  19  of the light guide plate  17  and the flexible printed board  16 , and light L leaking from a gap between the light source  12  and the light incident plane  18  of the light guide plate  17  passes to the outside through the gap between the light outgoing plane  19  and the flexible printed board  16  without passing through the light guide plate  17  as shown by an arrow of  FIG. 1 . As a result, although the gap between the light source  12  and the light incident plane  18  of the light guide plate  17  is covered with the flexible printed board  16 , an eye-shaped high-brightness region is generated near (portion designated by the letter P of  FIG. 1 ) an edge of the flexible printed board  16  in front of the light source  12 , and the region glitters like an eye when the surface light source apparatus  11  is obliquely observed, which remarkably impairs evenness in a light emission surface of the surface light source apparatus  11 . 
   Because a rim sheet (frame material) is overlapped on the flexible printed board  16 , when an opening of the rim sheet is decreased to extend an edge on an inner peripheral side of the opening of the rim sheet to the inside from an end on a light guide plate side of the flexible printed board  16 , the eye-shaped high-brightness region is hardly viewed. However, when the opening of the rim sheet is excessively decreased, because an effective region of the surface light source apparatus becomes small compared with an outer shape size of the surface light source apparatus, from a practical standpoint, it is difficult to excessively decrease the opening of the rim sheet. 
   In a backlight disclosed in Japanese Patent Application Laid-Open No. 2002-357823, gap between the light source and the light guide plate is covered with a light blocking tape. At this point, when the whole surface of the light blocking tape is bonded to the light outgoing plane of the light guide plate, an adhesive agent constitutes a light guide, the light leaks from between the light guide plate and the light blocking tape, and the edge of the light blocking tape also glitters like an eye. Therefore, in the backlight disclosed in Japanese Patent Application Laid-Open No. 2002-357823, only both ends of the light blocking tape are bonded to the light outgoing plane with an adhesive agent, and the light blocking tape is not bonded in at least the light source portion. 
   However, in the backlight disclosed in Japanese Patent Application Laid-Open No. 2002-357823, because the light blocking tape is not bonded to the light guide plate in the light source portion, the gap between the light blocking tape and the light guide plate is generated in that portion. Therefore, as with the surface light source apparatus shown in  FIG. 1 , the light leaks from the gap between the light guide plate and the light blocking tape, and the phenomenon in which the edge of the light blocking tape glitters like an eye cannot sufficiently be solved. 
   In a surface light source apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-321586, the flexible printed board adheres to the light guide plate with a double-sided adhesive tape. In the double-sided adhesive tape, a reflecting layer is formed on one of surfaces of a tape substrate, and a tackiness agent having a high light transmission property is provided on a surface of the reflecting layer. A colored layer is formed on the other surface of the tape substrate, and the tackiness agent having a high light transmission property is provided on a surface of the colored layer. The tackiness agent on the reflecting surface side of the double-sided adhesive tape adheres to the light guide plate, and the tackiness agent on the colored layer side adheres to the flexible printed board. Therefore, the light leaking from between the flexible printed board and the light guide plate is reflected by the reflecting layer, whereby the light is incident on the light guide plate. 
   However, in the surface light source apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-321586, the light passes through the tackiness agent of the double-sided adhesive tape adhering to the light guide plate, and the light leaks from the gap between the flexible printed board and the light guide plate. Even if the leaking light is reflected by the reflecting layer of the double-sided adhesive tape, at least part of the reflected light is transmitted through the light guide plate and reflected by the reflector plate on the back side, and the light is transmitted through the light guide plate again and outputted from the light outgoing plane. Therefore, even though the gap between the flexible printed board and the light guide plate is closed by the double-sided adhesive tape, there is no effect of eliminating the eye-shaped high-brightness region. 
   In a surface light source apparatus disclosed in Japanese Patent No. 3371052, end portions of the light guide plate and diffusing sheet are inserted into a recess provided in a front face of the light source, an end portion of the light outgoing plane of the light guide plate is covered with a case of the light source, and the end face of the diffusing sheet is covered with a light blocking wall provided in the case of the light source, a reflecting sheet in the light source and the like, thereby preventing the leakage of the light from the gap between the light guide plate and the case of the light source. 
   However, because a cold-cathode tube is used in the surface light source apparatus disclosed in Japanese Patent No. 3371052, the surface light source apparatus disclosed in Japanese Patent No. 3371052 cannot be applied to the surface light source apparatus having the light source in which a LED is used. That is, because the light source in which a LED is used is a micro component having a depth of several millimeters, a width of several millimeters, and a thickness not more than 1 mm, it is actually difficult that the end portions of the light guide plate and diffusing sheet are inserted into the recess of the light source, and the it is difficult to realize the practical application of the surface light source apparatus disclosed in Japanese Patent No. 3371052 for the light source in which a LED is used. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, an object of the present invention is to provide a surface light source apparatus which can prevent the generation of the eye-shaped high-brightness region, caused by the light leaking from the flexible printed board covering the gap between the light guide plate and the light source or from the gap between the light blocking member and the light guide plate, around the edge of the flexible printed board or light blocking member near the light source. 
   A surface light source apparatus according to a first aspect of the present invention includes a point light source; a light guide plate which spreads light introduced from the point light source into a planar shape to output the light from a light outgoing plane; and a light blocking member which covers parts of the point light source and the light outgoing plane of the light guide plate, wherein a gap shielding member is projected toward the light outgoing plane from a surface on a side facing the light outgoing plane of the light blocking member, and at least a portion facing the light outgoing plane in the gap shielding member is made of a material having a light blocking property. As used herein, the point light source shall mean a light source in which a micro light emitting element such as a LED is used. 
   In the surface light source apparatus according to the first aspect of the present invention, the gap between the light blocking member and the light outgoing plane of the light guide plate is closed by the gap shielding member, and at least the portion on which the light having relatively large luminosity is incident in the gap, i.e., the portion facing at least the light outgoing plane in the gap shielding member is made of the material having a light blocking property. Therefore, the phenomenon in which the light of the point light source leaks from the gap and glitters like an eye can be prevented to improve the evenness of the light emission surface. 
   A surface light source apparatus according to a second aspect of the present invention includes a point light source; a light guide plate which spreads light introduced from the point light source into a planar shape to output the light from a light outgoing plane; and a point light source mounting wiring board which is disposed to cover parts of the point light source and the light outgoing plane of the light guide plate, wherein a gap shielding member is projected toward the light outgoing plane from a surface on a side facing the light outgoing plane of the wiring board, and at least a portion facing the light outgoing plane in the gap shielding member is made of a material having a light blocking property. 
   In the surface light source apparatus according to the second aspect of the present invention, the gap between the wiring board and the light outgoing plane of the light guide plate is closed by the gap shielding member, and at least the portion on which the light having relatively large luminosity is incident in the gap, i.e., the portion facing at least the light outgoing plane in the gap shielding member is made of the material having a light blocking property. Therefore, the phenomenon in which the light of the point light source leaks from the gap and glitters like an eye can be prevented to improve the evenness of the light emission surface. 
   In the surface light source apparatus according to the second aspect of the present invention, preferably the gap shielding member is not projected toward a side of the point light source from an end face facing the point light source of the light guide plate, and the gap shielding member is not projected from an end on a side of the light outgoing plane of the wiring board. Accordingly, the wiring board is exposed between the point light source and the end face (light incident plane) of the light guide plate while the wiring board is not covered with the gap shielding member. Therefore, at least part of the light outputted onto the wiring board side between the point light source and the end face of the light guide plate is reflected by the wiring board and is incident on the light guide plate, which enables enhancement of the light use efficiency. Because the gap shielding member is not projected from the end on the light outgoing plane side of the wiring board, it is not necessary that the gap shielding member projected from the wiring board be hidden by the rim sheet, and the opening of the rim sheet can be widened to increase the effective area of the surface light source apparatus. 
   In the surface light source apparatus according to the first or second aspect of the present invention, preferably the whole of the gap shielding member is made of the material having the light blocking property. Accordingly, the light does not pass through the gap, which further improves the effect of preventing the eye-shaped high-brightness region. 
   In the surface light source apparatus according to the first or second aspect of the present invention, preferably the material having the light blocking property is a black material or a light absorbing material. Accordingly, because the light is not reflected by the gap shielding member, the stray light is hardly generated. 
   In the surface light source apparatus according to the first or second aspect of the present invention, preferably the gap shielding member is located in front of the point light source in a light outgoing direction. Accordingly, the gap shielding member can be provided to the necessity minimum. 
   In the surface light source apparatus according to the first or second aspect of the present invention, preferably the gap shielding member is located at least in front of the point light source in a light outgoing direction or both sides of the point light source when viewed from a direction perpendicular to the light outgoing plane of the light guide plate. Accordingly, because the light source is surrounded by the gap shielding member, the light of the light source hardly leaks in any direction, and the light emission surface of the surface light source apparatus can further be uniformalized. 
   A surface light source apparatus according to a third aspect of the present invention includes a point light source; a light guide plate which spreads light introduced from the point light source into a planar shape to output the light from a light outgoing plane; a diffusing sheet which is disposed while facing the light outgoing plane of the light guide plate; and a light blocking member which covers parts of the point light source, the light outgoing plane of the light guide plate, and the diffusing sheet, wherein a light absorbing layer is formed in a surface on a side facing the light outgoing plane of the light blocking member, and the light absorbing layer is brought into contact with a surface of the diffusing sheet. 
   In the surface light source apparatus according to the third aspect of the present invention, the light absorbing layer provided in the light blocking member is brought into contact with the diffusing sheet, the light of the point light source which enters the gap between the light blocking member and the light guide plate is diffused by the diffusing sheet, and the light is incident on the light absorbing layer of the light blocking member and absorbed by the light absorbing layer. Therefore, the phenomenon in which the light of the point light source leaks from the gap and glitters like an eye can be prevented to improve the evenness of the light emission surface. 
   In the surface light source apparatus according to the third aspect of the present invention, preferably a gap shielding member is projected toward a surface facing the light outgoing plane of the light blocking member at a position withdrawn from a front end of the light blocking member. At this point, the gap shielding member may be in contact with the surface light source apparatus, or may have a micro gap. Accordingly, the gap between the light blocking member and the light guide plate is closed to hardly pass the light by the gap shielding member. Even when the gap exists between the gap shielding member and the light guide plate, the light of the point light source which enters the gap between the gap shielding member and the light guide plate is diffused by the diffusing sheet, and the light is incident on the light absorbing layer of the light blocking member and absorbed by the light absorbing layer. Therefore, the phenomenon in which the light of the point light source leaks from the gap and glitters like an eye can be prevented to improve the evenness of the light emission surface. 
   In the surface light source apparatus according to the third aspect of the present invention, preferably a prism pattern is formed in a surface facing the light outgoing plane of the diffusing sheet. Accordingly, because the course of the light can be bent by the prism pattern, the course of the light passing through the gap between the light blocking member and the light guide plate or the light passing between the gap shielding member and light guide plate can be bent and absorbed more surely by the light absorbing surface of the light blocking member. 
   The means for solving the problem in the present invention has the feature in which the above-described constituent components are appropriately combined, and various variations of the present invention can be made by the combination of the components. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross-sectional view, partially broken away, of a schematic structure of a conventional surface light source apparatus; 
       FIG. 2  shows a cross-sectional view, partially broken away, of a schematic structure of a surface light source apparatus according to a first embodiment of the present invention; 
       FIG. 3A  shows a perspective view of a flexible printed board on which a light source is mounted, and  FIG. 3B  shows a plan view of the flexible printed board; 
       FIG. 4  shows a plan view of an enlarged light source portion of  FIG. 3B ; 
       FIG. 5A  shows a cross-sectional view taken along a line X-X of  FIG. 4 , and  FIG. 5B  shows a cross-sectional view taken along a line Y-Y of  FIG. 4 ; 
       FIG. 6  shows a schematic cross-sectional view for explaining action of the surface light source apparatus according to the first embodiment; 
       FIG. 7  shows a relationship between a radiation angle and a relative luminosity of a LED; 
       FIG. 8  shows a plan view of a flexible printed board in which a gap shielding member is provided in a different region; 
       FIG. 9  shows a cross-sectional view, partially broken away, of a schematic structure of a surface light source apparatus according to a second embodiment of the present invention; and 
       FIG. 10  shows a cross-sectional view, partially broken away, of a schematic structure of a surface light source apparatus according to a third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below with reference to the drawings. 
   First Embodiment 
     FIG. 2  shows a cross-sectional view, partially broken away, of schematic structure of a surface light source apparatus according to a first embodiment of the present invention. A surface light source apparatus  31  is used as a backlight for a liquid crystal display device. The surface light source apparatus  31  mainly includes a light source  33 , a light guide plate  34 , a reflector plate  35 , a diffusing sheet  36 , and a rim sheet  37  which are mounted on a flexible printed board  32 . 
   The light guide plate  34  is molded in a thin plate made of a transparent resin material having a high refractive index such as polycarbonate resin and polymethyl methacrylate (PMMA). Although a light outgoing plane  38  of the light guide plate  34  is formed in a substantially smooth surface, the light outgoing plane  38  is formed in a finely coarse surface when viewed closely. A number of fine deflection patterns  34   a  are formed in a surface (hereinafter referred to as back side) opposite the light outgoing plane  38  of the light guide plate  34 . The fine deflection pattern  34   a  totally reflects the light guided through the light guide plate  34  to output the light to the outside from the light outgoing plane  38 . There is no particularly limitation on the shape and the arrangement of the deflection patterns  34   a.  For example, a number of deflection patterns  34   a  which are recessed in the form of triangular grooves in the back side of the light guide plate  34  are coaxially arranged while substantially centered on the light source  33 . 
   The light emitted from the light source  33  is incident on the light guide plate  34  from a light incident plane  39  of the light guide plate  34 , and the light is totally reflected repeatedly between the back side and the light outgoing plane  38  of the light guide plate  34 . The light incident on the deflection pattern  34   a  during the total reflection between the back side and the light outgoing plane  38  is total-reflected from the deflection pattern  34   a  and outputted to the outside from the light outgoing plane  38 . 
   Because the reflector plate  35  faces the back side of the light guide plate  34 , the reflector plate  35  reflects the light leaking from the back side of the light guide plate  34  and returns the light into the light guide plate  34 , thereby improving the light use efficiency. 
   The diffusing sheet  36  is disposed on the light outgoing plane  38 , and a periphery on an upper surface side of the diffusing sheet  36  is covered with the frame-shape rim sheet  37 . Therefore, the light outgoing from the light outgoing plane  38  is diffused by the diffusing sheet  36  and outputted toward a front face. 
   The light source  33  is a light source (point light source) in which a LED  40  (chip) is used. The one light source  33  may be used in the surface light source apparatus  31  or a plurality of the light sources  33  may be used in the surface light source apparatus  31 . The LED  40  is sealed in a transparent resin  41 . An upper surface, a lower surface, right and left side faces, and a rear surface of the transparent resin  41  are covered with a case  42  made of a white resin. Therefore, the front face of the transparent resin  41  is exposed from a front opening of the case  42 . 
   When the LED  40  emits the light, the light from the LED  40  travels through the transparent resin  41  and outputted to the outside from the front face of the light source  33 , or the light is reflected one or a plurality of times at a boundary between the transparent resin  41  and case  42  and outputted to the outside from the front face of the light source  33 . 
   As shown in  FIGS. 3A and 3B , the light source  33  is mounted on the flexible printed board  32  along with an electronic component  43  such as a Zener diode. A gap shielding member  44  is formed in front of the light source  33  in the surface of the flexible printed board  32 . 
     FIG. 4  shows a plan view of the enlarged light source of  FIG. 3B ,  FIG. 5A  shows a cross-sectional view taken along a line X-X of  FIG. 4 , and  FIG. 5B  shows a cross-sectional view taken along a line Y-Y of  FIG. 4 . As shown in  FIG. 5A , in the flexible printed board  32 , a conductor layer  47  (pattern wiring) formed by a rolled copper foil having a thickness of 35 μm is laminated on a base film  45  made of polyimide having a thickness of 12.5 μm by an adhesive agent layer  46  having a thickness of 20 μm, and a cover film  49  made of polyimide having a thickness of 12.5 μm is further laminated on the conductor layer  47  by an adhesive agent layer  48  having a thickness of 25 μm. As shown in  FIG. 5B , in a portion where the light source  33  is mounted, the cover film  49  and the adhesive agent layer  48  are partially removed to expose the conductor layer  47 , the light source  33  is placed on the flexible printed board  32 , and an electrode provided on the lower surface of the light source  33  is soldered to the respective conductor layer  47  of the flexible printed board  32  with a solder  50 . Therefore, the lower surface of the case  42  of the light source  33  is aligned with the same height as the upper surface of the flexible printed board  32 . 
   As shown in  FIG. 4 , the gap shielding member  44  adheres to a front region of the light source  33  while being separated by a distance of a=0.25 mm from the front face of the light source  33 . In a longitudinal direction, the gap shielding member  44  is formed in symmetric in relation to a center line C passing through the center of the light source  33 , and an end of the gap shielding member  44  is withdrawn by b=0.6 mm from an end of the flexible printed board  32 . 
   As shown in  FIGS. 5A and 5B , the gap shielding member  44  is bonded onto a cover film  49  of the flexible printed board  32 . The gap shielding member  44  is formed by a light blocking layer  51 , a reinforcing plate  52 , and an adhesive agent layer  53  in order from the upper layer. The reinforcing plate  52  is formed by a thin plate made of polyimide. In the light blocking layer  51 , a surface treatment layer is formed on the surface of the reinforcing plate  52 , and silk-screen printing of a black coating material (for example, CR-18C-KT1 produced by Asahi Chemical Research Laboratory Co., Ltd.) is performed onto the surface treatment layer. The surface treatment layer includes an underlying layer made of Ni and an upper layer made of Au, and the surface treatment layer is formed by NiAu electrolytic plating. The surface of the black coating material is roughened and delustered. The adhesive agent layer  53  is a transparent thermosetting epoxy adhesive agent, and the gap shielding member  44  is adhesively bonded onto the flexible printed board  32  by the adhesive agent layer  53 . 
   As shown in  FIG. 6 , the thickness of the gap shielding member  44  is equal to a thickness e of the face on the mounting side of the case  42 . For example, in the present embodiment, the face on the mounting side of the case  42  has the thickness of 72.5 μm. Therefore, the gap shielding member  44  has the total thickness of 72.5 μm in which the light blocking layer  51  has the thickness of 12.5 μm, the reinforcing plate  52  has the thickness of 25 μm, and the adhesive agent layer  53  has the thickness of 35 μm. 
   The light source  33  thus mounted on the flexible printed board  32  is vertically inverted while the flexible printed board  32  is faced up, and the light source  33  is arranged to face the light incident plane  39  of the light guide plate  34 . The gap shielding member  44  provided in the flexible printed board  32  is brought into surface contact with an end portion in the light outgoing plane  38  of the light guide plate  34 . A height f of the transparent resin  41  of the light source  33  is equal to the thickness of the light guide plate  34 , and the light source  33  is disposed such that the center in the height direction of the transparent resin  41  coincides with the center in the thickness direction of the light guide plate  34 . Furthermore, because the thickness of the gap shielding member  44  is equal to the thickness e of the face on the mounting side of the case  42 , a gap is not generated between the surface of the light blocking layer  51  of the gap shielding member  44  and the light outgoing plane  38  of the light guide plate  34 . 
   Therefore, in front of the light source  33 , the gap between the flexible printed board  32  and the light outgoing plane  38  is closed by the gap shielding member  44 . Particularly, in the gap, the region adjacent to the light outgoing plane  38  is closed by the light blocking layer  51  and the reinforcing plate  52  which are of a light blocking material. As a result, the light emitted from the light source  33  hardly passes between the flexible printed board  32  and light outgoing plane  38 , and the eye-shaped high-brightness region is hardly generated at an edge of the flexible printed board  32  or rim sheet  37  to uniformize the light emission surface. 
   Because the gap shielding member  44  has the transparent adhesive agent layer  53 , the light incident on the gap shielding member  44  from the light source  33  is transmitted through the adhesive agent layer  53 . However, the light transmitted through the adhesive agent layer  53  has little influence due to a directivity characteristic as described below. As shown in  FIG. 6 , it is assumed that the height f of the transparent resin  41  is set to 650 μm, the distance d between the front face of the light source  33  and the light incident plane  39  is set to 250 μm, the thickness e on the mounting side of the case  42  is set to 72.5 μm, the thickness of the light blocking layer  51  is set to 12.5 μm, the thickness of the reinforcing plate  52  is set to 25 μm, and the thickness of the adhesive agent layer  53  is set to 35 μm. The light emitted to the direction ranging from 55° (θ 1 ) to 58° (θ 2 ) relative to an optical axis direction (perpendicular to the front face of the light source  33  and the light incident plane  39 ) is incident from the center of the front face of the light source  33  on an end face of the transparent resin  41 . 
   On the other hand, referring to a LED directivity characteristic curve of  FIG. 7 , in the case of the radiation angle θ 1 =58°, the relative luminosity becomes K of about 42% in  FIG. 7 . When the radiation angle ranges from 55° to 58°, the luminosity becomes only about 42 to 47% relative to a front-face luminosity (luminosity in the 0° direction), so that it does not matter because of the small luminosity. The fact can also be confirmed through experiments.  FIG. 7  shows a directivity characteristic of a LED (model name: NESW008C) presented by Nichia Corporation (http://www.nichia.co.jp/specification/jp/led_smd/NESW008CT.pdf). 
   Obviously, because the adhesive agent layer  53  desirably does not transmit the light, the (e.g. black) adhesive agent or tackiness agent having the light blocking property may be used as the adhesive agent layer  53 . 
   The end of the gap shielding member  44  on the side of the light source  33  is configured so as not to be projected toward the side of the light source  33  from the light incident plane  39 . When the gap shielding member  44  is projected from the light incident plane  39 , the light traveling upward in the gap between the light source  33  and the light incident plane  39  is absorbed by the gap shielding member  44 . On the contrary, when the gap shielding member  44  is not projected from the light incident plane  39 , the flexible printed board  32  is exposed in the upper portion of the gap between the light source  33  and the light incident plane  39 . Therefore, like a light beam L 1  shown in  FIG. 6 , the light traveling upward in the gap between the light source  33  and the light incident plane  39  is reflected by the flexible printed board  32  is incident on the light guide plate  34 , so that the light use efficiency can be enhanced. 
   The end of the gap shielding member  44  on the side opposite the light source  33  is configured so as not to be projected from the end of the flexible printed board  32 . When the gap shielding member  44  is projected from the end of the flexible printed board  32 , in order to hide the gap shielding member  44  projected from the flexible printed board  32 , it is necessary to further reduce the opening of the rim sheet  37 . Therefore, the effective region of the surface light source apparatus  31  is reduced by the reduced opening of the rim sheet  37 . 
   In the case where the light blocking layer  51  of the gap shielding member  44  has a light absorbing property, when the light blocking layer  51  comes into optically close contact with the light outgoing plane  38  of the light guide plate  34 , the light guided through the light guide plate  34  is absorbed by the light blocking layer  51  when entering the region where the light blocking layer  51  comes into close contact with the light outgoing plane  38 , which possibly causes loss. Therefore, in the surface light source apparatus  31 , the light outgoing plane  38  of the light guide plate  34  and/or the surface of the light blocking layer  51  are roughened such that the optically close contact is hardly established between the light outgoing plane  38  and the surface of the light blocking layer  51 . 
   As shown in  FIG. 8 , the gap shielding member  44  may be provided in the region surrounding the light source  33  in the surface of the flexible printed board  32 . Alternatively, the gap shielding member  44  may be provided in the form of a U-shape so as to surround the front face and side faces of the light source  33 . 
   Desirably the gap shielding member  44  is brought into contact with the light outgoing plane  38  of the light guide plate  34  to the extent where the gap shielding member  44  is not brought into close contact with the light outgoing plane  38 . However, a micro gap may be generated between the gap shielding member  44  and the light outgoing plane  38 . 
   Second Embodiment 
     FIG. 9  shows a cross-sectional view, partially broken away, of a schematic structure of a surface light source apparatus according to a second embodiment of the present invention. The rim sheet  37  whose surface constitutes a light absorbing tackiness agent layer is used in a surface light source apparatus  61 . That is, the rim sheet  37  is formed by a double-sided adhesive tape (for example, NITTO DENKO No. 532 black produced by NITTO DENKO CORPORATION), and the rim sheet  37  has the total thickness of 125 μm. In the double-sided adhesive tape, black tackiness agents  62  and  64  are applied onto both surfaces of a core material  63  made of transparent polyethylene terephthalate (PET). An end portion of a diffusing sheet  65  disposed above the light outgoing plane  38  of the light guide plate  34  is extended to a position below the rim sheet  37 , and the tackiness agent  64  in the lower surface of the rim sheet  37  is bonded to the upper surface of the diffusing sheet  65 . A fine diffusing pattern is formed in the upper surface of the diffusing sheet  65  to diffuse the light, and a prism pattern is formed in the lower surface of the diffusing sheet  65  to refract the light outputted from the light outgoing plane  38  in the direction perpendicular to the diffusing sheet  65 . 
   According to the surface light source apparatus  61  having the above structure, the light emitted from the light source  33  enters the gap between the rim sheet  37  and the light outgoing plane  38  of the light guide plate  34 , the light is incident on the lower surface (prism pattern) of the diffusing sheet  65 , a course of the light is bent upward, and the light is diffused by the upper surface of the diffusing sheet  65 . Therefore, the light incident on the diffusing sheet  65  passes through the diffusing sheet  65 , is incident on the lower surface of the rim sheet  37 , and is absorbed by the tackiness agent  64 . As a result, the generation of the eye-shaped high-brightness region can be prevented in front of the light source  33 . Particularly, the eye-shaped light spot viewable when observed from the direction ranging from 60° to 75° relative to the direction perpendicular to the light outgoing plane  38  can be eliminated in the present embodiment. 
   On the other hand, because the transparent tackiness agent is used in the conventional rim sheet, even if the rim sheet  37  is bonded to the diffusing sheet  65 , the light transmitted through the diffusing sheet  65  is guided through the transparent tackiness agent layer, and the light is outputted from the end of the rim sheet  37 . Therefore, there is no effect of eliminating the eye-shaped high-brightness region. 
   Although the flexible printed board  32  is not shown in the present embodiment, the flexible printed board  32  may be provided either on the upper side of the light source  33  or the lower side of the light source  33 . However, in the case where the flexible printed board  32  is disposed on the upper side of the light source  33 , it is necessary that the lower surface of the diffusing sheet  65  shall not be covered with the flexible printed board  32 . The tackiness agent  62  may be omitted. 
   Third Embodiment 
     FIG. 10  shows a cross-sectional view, partially broken away, of a schematic structure of a surface light source apparatus according to a third embodiment of the present invention. In a surface light source apparatus  71 , a light blocking tape is bonded to the lower surface of a light blocking member  72  to project a gap shielding member  73 . The light blocking member  72  is formed by a rim sheet or a light blocking tape. In the case where the light blocking member  72  is formed by a rim sheet, the light blocking tape which is of the gap shielding member  73  is bonded to the lower surface. In the case where the light blocking member  72  is formed by a light blocking tape, after the two layers of the light blocking tape are formed, an unnecessary portion of the lower-layer light blocking tape is removed to form the gap shielding member  73 . 
   A diffusing sheet  74  is disposed on the light outgoing plane  38  of the light guide plate  34 , and a prism pattern  75  is formed in the lower surface of the diffusing sheet  74 . The gap shielding member  73  projected toward the lower surface of the light blocking member  72  such as the rim sheet and the light blocking tape is made to face the light outgoing plane  38  of the light guide plate  34 , and the lower surface of the light blocking member  72  is brought into contact with the upper surface of the diffusing sheet  74 . 
   In the present embodiment, the gap shielding member  73  may be in contact with the light outgoing plane  38  of the light guide plate  34 , and the gap between the fight blocking member  72  and the light outgoing plane  38  may be closed by the gap shielding member  73 . In this case, because the gap between the light blocking member  72  and the light outgoing plane  38  is closed by the gap shielding member  73 , the light never leaks from the gap between the light blocking member  72  and the light outgoing plane  38 , which makes it possible to prevent the generation of the eye-shaped high-brightness region near the end portion of the light blocking member  72 . 
   In the present embodiment, in the case where the light blocking member  72  is formed by a light absorbing material, a micro gap may be formed between the gap shielding member  73  and the light outgoing plane  38  as shown in  FIG. 10 . In this case, after the gap between the light blocking member  72  and the light guide plate  34  is shielded by the gap shielding member  73  to make the light hardly pass therethrough, the course of the light passing between the gap shielding member  73  and the light outgoing plane  38  is bent upward by the prism pattern  75 . Then, the light is diffused by the diffusing sheet  74 , is incident on the light blocking member  72 , and is absorbed by the light blocking member  72 . Therefore, the light never leaks from the gap between the light blocking member  72  and the light outgoing plane  38 , and the generation of the eye-shaped high-brightness region can be prevented near the end portion of the light blocking member  72 . 
   Although the flexible printed board  32  is not shown in the present embodiment, the flexible printed board  32  may be provided either on the upper side of the light source  33  or the lower side of the light source  33 .