Patent Publication Number: US-2009237592-A1

Title: Planar Illumination Device

Description:
TECHNICAL FIELD 
     The present invention relates to a side-light-type planar illumination device and particularly to a planar illumination device used as illuminating means of a liquid crystal display device. 
     BACKGROUND ART 
     A liquid crystal display device is widely used in display means or the like of electronic equipment at present but since the liquid crystal display device is not self-luminous, illuminating means for ensuring visibility at night and in dark places is needed. A planar illumination device has been used as such illuminating means. 
     As a mode of the planar illumination device, a side-light-type planar illumination device is widely used. The side-light-type planar illumination device comprises a light guide plate with light transmittance, a rod-state light source arranged on a side end face of the light guide plate or one or more point-like light source as basic elements. As a recent trend, in accordance with an increase in applications of planar illumination devices to small-sized electronic equipment such as personal digital assistant, a planar illumination device of the type provided with a point-like light source capable of simplification of a driving circuit is used, and a white LED (hereinafter also referred to simply as an LED) is frequently used as a point-like light source. 
     This type of LED is usually mounted on a circuit board such as a flexible print circuit (hereinafter also referred to as FPC) and arranged on the side end face of the light guide plate, and in this configuration, one of major faces of the FPC and the light guide plate are fixed together in the prior art (See Patent Document 1, for example). 
       FIG. 6  is a side view schematically illustrating a planar illumination device having the above configuration. A planar illumination device  100  shown in  FIG. 6  comprises a light guide plate  101 , an LED  103 , and an FPC  102  on which the LED  103  is mounted, and the LED  103  is arranged on a side end face  108  by fixing a front portion of the FPC  102  to a major face  107  of the light guide plate  101  by fixing means  106  such as a double-sided adhesive tape. By fixing the FPC  102  and the light guide plate  101  in this way, the arrangement position of the LED  103  is held stably, and the connection efficiency between the LED  103  and the light guide plate  101  can be maintained favorably, which is advantageous. Here, the LED  103  usually has a translucent resin that seals an LED chip, not shown, and a sheath  105  made of a white resin or the like is provided on the periphery of the translucent resin  104 . Typically, in the vicinity of the center part of a face  109  opposed to the side end face  108  of the light guide plate  101  of the LED  103 , a through hole or a slit is provided in the sheath  105  so that the face  109  is to be used as a major light-emitting face. 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-213943 (Claim  3 ,  FIG. 2 ) 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     Since a planar illumination device using an LED plays a role as illuminating means for a liquid crystal display device, further thinning is in demand all the time while promoting higher and more uniform brightness. Thus, from a viewpoint of increase in light taking-out efficiency from an LED chip and no need of the thickness for a sheath, an LED formed with an exposed translucent resin that seals the LED chip is preferably used. However, the above configuration using such an LED has the following problem. 
       FIG. 7  is a side view of a conventional planar illumination device illustrating the same configuration as in  FIG. 6  when the LED formed with the exposed translucent resin that seals the LED chip is used. In a planar illumination device  200  shown in  FIG. 7 , an LED  110  is formed of a board portion  110   b  on which an LED chip, not shown, is mounted and a light-emitting portion  110   a  made of a translucent resin that seals the LED chip, and the light-emitting portion  110   a  has no sheath on the periphery but is exposed. Since this LED  110  functions as a light-emitting face over the entire surface of the light-emitting portion  110   a , there is a problem of lost light as a light path P 1  and a light path P 2  shown in  FIG. 7 , not utilized as illumination light, since the light is absorbed by or passed through the FPC  102  and the double-sided adhesive tape  106 . In order to solve the problem, even if some reflecting means are laminated and arranged on the FPC  102 , for example, its effect is not sufficient. 
     The present invention was made in view of the above problem and has an object to accelerate thinning of a planar illumination device using an LED while promoting higher and more uniform brightness. 
     Means for Solving the Problems 
     In order to solve the above problem, a planar illumination device according to the present invention provided with a plate-state light guide plate, an LED arranged on a side end face of the light guide plate, and a circuit board, on which the LED is mounted, in which the LED is made of a translucent resin that seals an LED chip and has a light-emitting portion not having a sheath but being exposed, mounted on the circuit board with the light-emitting portion projecting from an outline of the circuit board and arranged so that the light-emitting portion is not projected from the side end face of the light guide plate in a direction crossing the light guide plate, and reflecting means covering the light-emitting portion is provided. 
     According to the present invention, since the translucent resin that seals the LED chip is exposed, an increase for the thickness of the sheath is not generated, but thinning of the planar illumination device is promoted. Moreover, by mounting the LED with the light-emitting portion projecting from the outline of the circuit board and arranging the light-emitting portion not projecting from the side end face of the light guide plate in a direction crossing the light guide plate, while reflecting means covering the light-emitting portion of the LED is provided, generation of lost light is minimized, and high light taking-out efficiency of the LED with the exposed translucent resin is fully utilized, which contributes to higher brightness of the planar illumination device. 
     In one mode of the present invention, the light guide plate has a notch portion accommodating the light-emitting portion of the LED on the side of the side end face on which the LED of the light guide plate is arranged. By this arrangement, the entire side face of the light-emitting portion of the LED is brought into close contact with the light guide plate, and light emission distribution of the light incident from the LED to the light guide plate can be made equal to the light emission distribution of the light by a single LED, which contributes to more uniform brightness of the planar illumination device. 
     Also, in one mode of the present invention, the light guide plate has a stepped part provided with a step on one of major faces of the light guide plate on the side end face on which the LED of the light guide plate is arranged, the stepped portion accommodates fixing means having an adhesive layer on both faces, and the circuit board is fixed to the light guide plate through the fixing means. 
     The circuit board is preferably formed in a comb form with a base portion and a plurality of arm portions extending from the base portion, the LED is mounted on the circuit board so that the light-emitting portion is arranged between the pair of arm portions, and the stepped portion in which the fixing means is accommodated of the light guide plate may be provided at a position corresponding to each of the plurality of arm portions. 
     By making the circuit board in the above predetermined shape, generation of lost light can be minimized, the high light taking-out efficiency of the LED with the exposed translucent resin can be fully utilized, and by fixing the circuit board to the light guide plate, the LED is stably held on the side end face of the light guide plate, and high connection efficiency between the LED and the light guide plate can be achieved. 
     Alternatively, the stepped portion accommodating the fixing means in the light guide plate may be provided as a projected portion extending from the side end face on which the LED of the light guide plate is arranged, by which the circuit board can be fixed to the light guide plate while the entire light guide plate is supported by the projected portion. This configuration is advantageous in improvement of robustness around a light source of the planar illumination device since the FPC can be fixed to the light guide plate without room for deformation such as bending when a flexible print circuit (FPC) having flexibility is used as the circuit board. 
     Moreover, in one mode of the present invention, the reflecting means may have an adhesive layer at least on one face side, and the back face of the circuit board and one of major faces of the light guide plate may be fixed by the reflecting means. Similarly, when the reflecting means has an adhesive layer at least on its one face side, the light-emitting portion of the LED and one of the major faces of the light guide plate may be fixed by the reflecting means. 
     By fixing the circuit board or the light-emitting portion of the LED mounted on the circuit board and one of the major faces of the light guide plate by the reflecting means having an adhesive layer, the planar illumination device according to the present invention can be put into practice with a relatively simple configuration and at a low cost. 
     ADVANTAGES OF THE INVENTION 
     Since the present invention was configured as above, the high light taking-out efficiency of the LED formed so that the translucent resin that seals the LED chip is exposed can be fully utilized, and reduction in thickness of the planar illumination device can be accelerated while promoting higher and more uniform brightness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  are diagrams illustrating an essential part of a planar illumination device in a first embodiment of the present invention, in which  FIG. 1(   a ) is an exploded plan view,  FIG. 1(   b ) is an A-A sectional view showing an assembled state of the device in  FIG. 1(   a ), and  FIG. 1(   c ) is a B-B sectional view showing the assembled state of the device in  FIG. 1(   a ). 
         FIG. 2  are diagrams illustrating an essential part of a planar illumination device in a second embodiment of the present invention, in which  FIG. 2(   a ) is an exploded plan view and  FIG. 2(   b ) is an A-A sectional view in an assembled state of the device in  FIG. 2(   a ). 
         FIG. 3  is a sectional view illustrating another example of reflecting means in a planar illumination device in a third embodiment of the present invention. 
         FIG. 4  are diagrams illustrating an essential part of a planar illumination device in a third embodiment of the present invention, in which  FIG. 4(   a ) is an exploded plan view and  FIG. 4(   b ) is a side view in an assembled state of  FIG. 4(   a ). 
         FIG. 5  are diagrams illustrating an essential part of a planar illumination device in a fourth embodiment of the present invention, in which  FIG. 5(   a ) is an exploded plan view and  FIG. 5(   b ) is a side view in an assembled state of  FIG. 5(   a ). 
         FIG. 6  is a side view schematically illustrating configuration of a conventional planar illumination device. 
         FIG. 7  is a side view schematically illustrating configuration of a conventional planar illumination device when an LED with an exposed translucent resin that seals an LED chip is used. 
     
    
    
     REFERENCE NUMERALS 
     
         
         
           
               10 ,  30 ,  50 ,  70 : Planar illumination device 
               2 ,  32 ,  52 ,  72 : Light guide plate 
               3 ,  33 ,  53 ,  73 : Side end face opposing LED 
               11 ,  31 : Flexible print circuit (circuit board) 
               21 ,  22 ,  23 : LED 
               21   a ,  22   a ,  23   a : Light emitting portion 
               35 ,  36 ,  37 ,  75 ,  76 ,  77 : Notch portion 
               25 ,  38 : Reflecting means 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described below on the basis of the attached drawings.  FIGS. 1 to 5  are diagrams for explanation and do not necessarily reflect actual dimensions or ratios accurately. 
       FIG. 1  are diagrams illustrating an essential part of a planar illumination device in a first embodiment of the present invention, in which  FIG. 1(   a ) is an exploded plan view,  FIG. 1(   b ) is an A-A sectional view showing an assembled state of the device in  FIG. 1(   a ), and  FIG. 1(   c ) is a B-B sectional view showing the assembled state of the device in  FIG. 1(   a ). A planar illumination device  10  shown in  FIG. 1  comprises a plate-state light guide plate  2 , three LEDS  21  to  23  arranged on a side end face  3  of the light guide plate  2 , a flexible print circuit (FPC)  11 , which is a circuit board in this embodiment and on which the LEDs  21  to  23  are mounted, and a reflector  25 , which is reflecting means in this embodiment. 
     In this embodiment, the LEDs  21  to  23  are formed of board portions  21   b  to  23   b  on which LED chips (not shown) are mounted and light-emitting portions  21   a  to  23   a  made of a translucent resin that seals the LED chips and not having a sheath (and internal components such as a lamp house) but exposed. 
     The FPC  11  is formed in a comb form with a base portion  12  and four arm portions  15  to  18  extending to the front (in the direction of the light guide plate  2 ) from the base portion  12 . In each of the LEDs  21  to  23 , only their board portions  21   b  to  23   b  are mounted on the FPC  11  with the light-emitting portions  21   a  to  23   a  mounted on the FPC  11  and projecting from the outline of the FPC  11 . Also, the LEDs  21  to  23  are arranged with the respective light-emitting portions  21   a ,  22   a ,  23   a  located between a pair of arm portions  15 - 16 ,  16 - 17 ,  17 - 18  so that the light-emitting portions  21   a  to  23   a  are not covered by the FPC  11 . 
     Moreover, the light guide plate  2  has recess portions  5  to  8 , which are stepped portions in this embodiment, on the side of the side end face  3  on which the LEDs  21  to  23  are arranged on a major face  4 , and in each of the recess portions  5  to  8  provided at positions corresponding to each of the arm portions  15  to  18 , fixing means (See reference numeral  27  in  FIG. 1(   b )) such as a double-sided adhesive tape is accommodated. 
     As shown with the arm portion  16  as an example in the A-A sectional view in  FIG. 1(   b ), the distal end portions of the arm portions  15  to  18  of the FPC  11  are affixed by the fixing means  27  accommodated in the recess portions  5  to  8  and the FPC  11  is fixed to the light guide plate  2  so that a mounting surface  11   a  becomes substantially flush with the major face  4  of the light guide plate  4 , and the reflector  25  is laminated and arranged on the FPC  11 . 
     By the above configuration, the LEDs  21  to  23  in this embodiment have their light-emitting portions  21   a  to  23   a  arranged on the side end face  3  without projecting from the side end face  3  of the light guide plate  2  in a direction crossing the light guide plate  2  (vertical direction in the sectional view in  FIGS. 1(   b ) and  1 ( c )). By this configuration, the lost light caused by a light path such as the light path P 2  shown in  FIG. 7  is not generated but the LEDs  21  to  23  can be stably held on the side end face  3  of the light guide plate  2 . 
     Also, as shown by the LED  21  as an example in the B-B sectional view in  FIG. 1(   c ), since the FPC  11  is not interposed between the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  and the reflector  25 , light emitted in the direction of the major face  4  from the LEDs  21   a  to  23   a  can be directly reflected by the reflector  25  as a light path P 3  and can be made incident to the side end face of the light guide plate  2  efficiently. 
     The reflector  25  in this embodiment is preferably a regular reflecting means, and specifically, a film on which metal such as silver is deposited, a metal plate such as an aluminum plate subjected to mirror machining or a film provided with a reflection layer in a multi-layered structure of a polymer thin film can be used. Also, diffusion reflecting means such as a white film obtained by making a resin base white by foaming or diffusion of a white pigment may be used. Also, in this embodiment, the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  are covered by the integrally formed reflector  25 , but the reflecting means according to the present invention may be formed of a plurality of reflecting means individually covering the light-emitting portions  21   a ,  22   a ,  23   a  of the LED  21 ,  22 ,  23 , respectively. 
     Next, referring to  FIGS. 2 to 5 , other embodiments of the present invention will be described, but common components are given the same reference numerals in each embodiment including the above first embodiment so that explanation of duplicated portions is omitted as appropriate but features of each embodiment will be described in detail. 
       FIG. 2  are diagrams illustrating an essential part of a planar illumination device of a second embodiment of the present invention, in which  FIG. 2(   a ) is an exploded plan view and  FIG. 2(   b ) is an A-A sectional view showing an assembled state of the device in  FIG. 2(   a ). A planar illumination device  70  shown in  FIG. 2  is provided with a plate-state light guide plate  72 , three LEDs  21  to  23  arranged on a side end face  73  of the light guide plate  72 , an FPC  31  on which the LEDs  21  to  23  are mounted, and the reflector  25 . 
     In the planar illumination device  70  in this embodiment, the FPC  31  is formed substantially in a rectangular shape, and the LEDs  21  to  23  have only their board portions  21   b  to  23   b  mounted on the FPC  31  with the light-emitting portions  21   a  to  23   a  mounted on the FPC  31  and projecting from the outline of the FPC  31  as in the above-mentioned first embodiment. Also, in the light guide plate  72 , notch portions  75  to  77  for accommodating the light-emitting portions  21   a  to  23   a , respectively, are formed on the side end face  73  on which the LEDs  21  to  23  are arranged, and projected portions  81  to  84  extending from a portion where there is no notch portions  75  to  77  on the side end face  73  are provided integrally with the light guide plate  72 . 
     Here, as shown in  FIG. 2(   b ) with the projected portion  82  as an example, the projected portions  81  to  84  are formed having a step with respect to a major face  74  so as to constitute a stepped portion in this embodiment. Moreover, on each of the projected portions  81  to  84 , the fixing means  27  such as a double-sided adhesive tape is accommodated. In this embodiment, the FPC  31  is fixed to the projected portions  81  to  84  so that portions corresponding to each of the projected portions  81  to  84  are affixed to the fixing means  27  during assembly, respectively, and a mounting surface  31   a  becomes substantially flush with the major face  74  of the light guide plate  72 , and the reflector  25  is laminated and arranged on the FPC  31 . At this time, as shown in  FIG. 2(   b ) with the LED  22  as an example, the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  are accommodated in the corresponding notch portions  75  to  77 , respectively, and arranged on the side end face  73 . 
     By the above configuration, the LEDS  21  to  23  in this embodiment have their light-emitting portions  21   a  to  23   a  arranged on the side end face  73  without projecting from the side end face  73  of the light guide plate  72  in the direction crossing the light guide plate  72  (vertical direction in the sectional view in  FIG. 2(   b )), and the reflector  25  directly covers the light-emitting portions  21   a  to  23   a  of the LEDS  21  to  23  without the FPC  31  interposed therebetween. By this configuration, the planar illumination device  70  in this embodiment obtains actions and effects equivalent to those of the planar illumination device  10  in the above-mentioned first embodiment. 
     In addition, in the planar illumination device  70  in this embodiment, by accommodating the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  in the notch portions  75  to  77 , the entire side faces of the light-emitting portions  21   a  to  23   a  are brought into close contact with the light guide plate  72 , and light emission distribution of the light incident to the light guide plate  72  from the LEDS  21  to  23  can be made equivalent to the light emission distribution of the light by the single LED. 
     Though the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  are all accommodated in the notch portions  75  to  77  of the light guide plate  72  in this embodiment, only a part of the light-emitting portions  21   a  to  23   a  may be contained in the notch portions  75  to  77 . 
     Moreover, in this embodiment, since the FPC  31  is fixed to the light guide plate  72  in a way that the entire FPC  31  is supported by the projected portions  81  to  84 , the FPC  31  can be fixed to the light guide plate  72  without room for deformation such as bending, which is advantageous in improvement of robustness around a light source of the planar illumination device  70  as compared with the fixing method in the planar illumination device  10  shown in  FIG. 1  in which the FPC  11  is fixed to the light guide plate  2  using the arm portions  15  to  18  extending in front of the FPC  11 . 
     According to the present invention, it is only necessary for the reflector  25  to cover at least the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23 , and the reflector  25  may be arranged in abutment with the FPC  31  from the side of the light guide plate  72  as shown in  FIG. 3 , for example. Such arrangement of the reflector  25  can be similarly put into practice in the case of the planar illumination device  10  shown in  FIG. 1  by forming the reflector  25  in a comb form having arm portions provided in a complementary manner with the arm portions  15  to  18  of the FPC  11  or by forming a plurality of reflectors individually covering each of the light-emitting portions  21   a  to  23   a  and arranging the arm portions or the individual reflectors between the pair of arm portions  15 - 16 ,  16 - 17  and  17 - 18 , respectively. 
       FIG. 4  are diagrams illustrating an essential part of a planar illumination device in a third embodiment of the present invention, in which  FIG. 4(   a ) is an exploded plan view and  FIG. 4(   b ) is a side view showing an assembled state of the device in  FIG. 4(   a ). A planar illumination device  30  shown in  FIG. 4  is formed of a plate-state light guide plate  32 , three LEDs  21  to  23  arranged on a side end face  33  of the light guide plate  32 , the FPC  31  on which the LEDs  21  to  23  are mounted, and a reflector  38 , which is the reflecting means in this embodiment. 
     In the planar illumination device  30  in this embodiment, the FPC  31  is formed substantially in the rectangular shape, the LEDs  21  to  23  have only their board portions  21   b  to  23   b  mounted on the FPC  31  as in the above-mentioned first embodiment and the light-emitting portions  21   a  to  23   a  mounted on the FPC  31  and projecting from the outline of the FPC  31 . Also, in the light guide plate  32 , notch portions  35  to  37  for accommodating each of the light-emitting portions  21   a  to  23   a  are formed on the side end face  33  on which the LEDs  21  to  23  are arranged. 
     As shown in  FIG. 4(   b ), in the planar illumination device  30  in this embodiment, the reflector  38  has an adhesive layer  38   b  at least on its one face side in addition to a reflection layer  38   a  similar to the reflector  25  in the above-mentioned first and second embodiments, and the FPC  31  is arranged with a back face  31   b  on the side opposite to the mounting face substantially flush with a major face  34  of the light guide plate  32  and fixed to the major face  34  of the light guide plate  32  by the reflector  38  also functioning as the fixing means. At this time, as shown in  FIG. 4(   b ) with the LED  21  as an example, the light-emitting portions  21   a  to  23   a  of the LEDS  21  to  23  are accommodated in the corresponding notch portions  35  to  37 , respectively, and arranged on the side end face  33 . 
     The reflector  38  may have an adhesive layer  38   b  on one entire face side thereof but preferably does not have the adhesive layer  38   b  in areas facing the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  so that the reflection layer  38   a  is directly opposed to the light-emitting portions  21   a  to  23   a  in those areas. 
     By the above configuration, the planar illumination device  30  in this embodiment can obtain actions and effects equivalent to those of the planar illumination device  10  in the above-mentioned first embodiment, but in the planar illumination device  30 , by accommodating the light-emitting portions  21   a  to  23   a  of the LEDS  21  to  23  in the notch portions  35  to  37 , the entire side faces of the light-emitting portions  21   a  to  23   a  are brought into close contact with the light guide plate  32 , and light emission distribution of the light incident to the light guide plate  32  from the LEDs  21  to  23  can be made equivalent to the light emission distribution of the light by a single LED and at the same time, the planar illumination device having such action and effect can be realized by relatively simple configuration and at a lower cost. 
     Though the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  are all accommodated in the notch portions  35  to  37  of the light guide plate  32  in this embodiment, only a part of the light-emitting portions  21   a  to  23   a  may be contained in the notch portions  35  to  37 . 
       FIG. 5  are diagrams illustrating an essential part of a planar illumination device in a fourth embodiment of the present invention, in which  FIG. 5(   a ) is an exploded plan view and  FIG. 5(   b ) is a side view in an assembled state of  FIG. 5(   a ). A planar illumination device  50  shown in  FIG. 5  comprises a plate-state light guide plate  52 , three LEDs  21  to  23  arranged on a side end face  53  of the light guide plate  52 , the FPC  31  on which the LEDs  21  to  23  are mounted, and the reflector  38 , which is the reflecting means in this embodiment. 
     Components of the planar illumination device  50  in this embodiment are the same as those in the above-mentioned third embodiment, but they are different from the view point that the light guide plate  52  is formed substantially in a rectangular shape not having a notch portion. As shown in  FIG. 5(   b ) with the LED  21  as an example, the LEDs  21  to  23  are arranged so that top faces  21   c  to  23   c  of the light-emitting portions  21   a  to  23   a  are substantially flush with a major face  54  of the light guide plate  52  and arranged on the side end face  53  by fixing the top faces  21   c  to  23   c  of the light-emitting portions  21   a  to  23   a  to the major face  54  of the light guide plate  52  by the reflector  38  also functioning as the fixing means. 
     By the above configuration, a planar illumination device having actions and effects equivalent to those of the planar illumination device  10  in the above first embodiment can be realized with relatively simple configuration and at a lower cost. 
     Preferred embodiments of the present invention have been described above, but the planar illumination device according to the present invention is not limited to the above-mentioned embodiments, but in the first to fourth embodiments, the light guide plates  2 ,  52  may have a notch portion similar to the notch portions  75  to  77 ,  35  to  37  in the light guide plates  72 ,  32  in the second and third embodiments, for example, or the light guide plates  72 ,  32  in the second and third embodiments may be used without providing the notch portions  75  to  77 ,  35  to  37 . 
     Also, in the above-mentioned first and second embodiments, the reflector  25  may have an adhesive layer such as a double-sided adhesive tape affixed to its one face side, for example, similarly to the reflector  38 , by which it is fixed to the FPC  11 ,  31  or the light guide plates  2 ,  72 . At this time, similarly to the reflector  38 , areas facing the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  preferably do not have an adhesive layer but the reflection layer of the reflector  25  is directly opposed to the light-emitting portions  21   a  to  23   a  to those areas. 
     Also, through  FIGS. 1 to 5 , front sides of the light-emitting portions  21   a  to  23   a  of the LEDs  21  to  23  (faces opposed to the side end face of the light guide plate) are shown in a flat state, but the LED according to the present invention is not limited to that mode, but the light-emitting portions  21   a  to  23   a  may have a projection portion made of a cylindrical face, spherical face or the like. In this case, the outline of the notch portions  75  to  77 ,  35  to  37  are preferably formed in a profile in conformity with the outline of the projection portion. 
     Moreover, it is needless to say that the present invention is not limited to the number of LEDs used in the planar illumination device.