Abstract:
A surface illumination device has a light source, and a light guide plate having a light-emitting surface. The light guide plate guides light from the light source such that the light is emitted from a display region of the light-emitting surface. A plurality of deflection patterns having deflection inclined surfaces are formed in the display region in at least one of the light-emitting surface of the light guide plate and an opposite surface to the light-emitting surface. A light control structure that reduces light is provided on at least part of at least one of the light-emitting surface of the light guide plate and a surface except the opposite surface to the light-emitting surface, the light being reflected toward the display region by the surface.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a surface illumination device. Specifically, the present invention relates to a surface illumination device, which is used in display while incorporated in mobile devices such as a smartphone and a tablet computer. 
         [0003]    2. Related Art 
         [0004]    In the smartphone, the tablet computer, an electronic book reader, and the like, an icon is lighted in a position of a switch, and the position and a type of the switch is expressed by the icon. For example, in a smartphone  11  in  FIG. 1(A) , an icon  13  is displayed below a liquid crystal display screen  12 . Although the icon  13  is expressed by a character “A” in  FIGS. 1(A) , actually design marks such as a house and a magnifying glass are frequently used. When the icon  13  is pressed by a finger, a switch  14  provided beneath the icon  13  is turned on to switch a function of the smartphone  11 . 
         [0005]      FIG. 1(B)  illustrates a surface illumination device  15  for the display, which is incorporated in a lower portion of the smartphone  11  in  FIG. 1(A) .  FIG. 2(A)  illustrates a schematic section of the surface illumination device  15 . The surface illumination device  15  includes a light guide plate  16  and a light source  17 . The light guide plate  16  is molded using a transparent material, such as a polycarbonate (PC) resin and a polymethylmethacrylate (PMMA) resin, which has a high refractive index. The light source  17  is a minute light source (a point light source) in which an LED is used, and the light source  17  is disposed while a light exit window is opposed to one (light incident end face  16   a ) of end faces of the light guide plate  16 . Many minute prism deflection patterns  18  are formed in a lower surface (sometimes an upper surface) of the light guide plate  16 , and an icon-shaped display unit  19  is constructed by a set of deflection patterns  18  as illustrated in  FIG. 2(B) . The deflection patterns  18  are arrayed into an arc shape about a point near the light source  17 , and extend in directions along the arc about the point. A thin, flexible light guide sheet is used as the light guide plate  16  in the case that the switch  14  is disposed beneath the display unit  19 . 
         [0006]    When the light source  17  emits light in the surface illumination device  15 , the light incident to the light guide plate  16  from the light incident end face  16   a  is guided in the light guide plate  16  while totally reflected by the upper surface, the lower surface, and both side surfaces of the light guide plate  16 . When the light guided in the light guide plate  16  reaches the display unit  19  as illustrated in  FIG. 2(A) , the light is totally reflected by a deflection reflecting surface  18   a  of the deflection pattern  18 . In the light totally reflected upward by the deflection reflecting surface  18   a,  the light incident to the upper surface (a light-emitting surface  16   c ) of the light guide plate  16  at an angle smaller than a total reflection critical angle is transmitted through the light incident end face  16   a  to emit upward (the light is transmitted while refracted by the deflection pattern  18  in the case that the deflection pattern  18  is provided in the light-emitting surface  16   c ). As a result, the light emits into the icon shape to light the icon  13  of the smartphone  11 . 
         [0007]    However, in the smartphone  11  in which the surface illumination device  15  is used, when a user vertically inclines the smartphone  11  while holding the smartphone  11  in the hand, unfortunately luminance of the icon  13  repeats being brightened and darkened, and the icon  13  is seen while flickering. The reason the phenomenon is generated will be described with reference to  FIGS. 3 and 4 .  FIG. 3(B)  illustrates a directional pattern of the light emitting from the light-emitting surface  16   c  of the light guide plate  16  when the directional pattern is viewed from a direction (a Z-direction) perpendicular to the light-emitting surface  16   c,  an X-direction indicates a length direction (a crosswise direction of the smartphone  11 ) of the light guide plate  16 , and a Y-direction indicates a width direction (a longitudinal direction of the smartphone  11 ) of the light guide plate  16 . 
         [0008]    In the case that the light emitted from the small light source  17  is totally reflected by the deflection pattern  18  to emit from the light-emitting surface  16   c , because the light headed from the light source  17  to certain deflection pattern  18  is the light having a narrow range when viewed from the direction perpendicular to the light-emitting surface  16   c,  the light emitting from the light-emitting surface  16   c  also has the narrow directivity. That is, light La that goes straight to reach the display unit  19  or the deflection pattern  18  as illustrated in  FIG. 3(A)  has a directional pattern Ca that is lengthened in the X-direction as illustrated in Fig.  3 (B). Therefore, although the light having the directional pattern Ca can be recognized with high luminance from the front direction of the smartphone  11 , the light becomes dark when the smartphone  11  is vertically inclined. 
         [0009]    In the light incident to the display unit  19 , part of the light is incident to the deflection pattern  18  after totally reflected by a side surface  16   b  of the light guide plate  16  like light Lb in  FIG. 3(A) . As indicated by a broken line in  FIG. 2(A) , the light Lb is obliquely incident to the deflection pattern  18  and totally reflected toward the oblique direction by the deflection pattern  18 . Therefore, the light Lb emitting from the light-emitting surface  16   c  has a narrow directional pattern Cb that is inclined as illustrated in  FIG. 3(B) . 
         [0010]    As described above, because the light Lb having the directional pattern Cb is added to the light La having the directional pattern Ca, a bright region B and a dark region D are alternately generated when viewed from the X-direction (a substantially vertical direction when the user holds the smartphone  11  in the hand) as illustrated in  FIG. 4 . Therefore, when the user vertically inclines the smartphone  11 , a sight line alternately passes through the bright region B and the dark region D, and the icon  13  is seen while flickering. 
         [0011]    Patent Document 1: Japanese Unexamined Patent Publication No. 2001-243822 
       SUMMARY 
       [0012]    One or more embodiments of the present invention provides a surface illumination device that can remove extra stray light degrading visual quality of the display such as the icon. Particularly one or more embodiments of the present invention provides a surface illumination device that can reduce a phenomenon in which the display is seen while flickering when the seeing position is changed in a plane orthogonal to the direction of the light toward the display unit from the light source. 
         [0013]    In accordance with one or more embodiments of the present invention, a surface illumination device includes: a light source; and a light guide plate that causes light guided from the light source to emit from a display region of a light-emitting surface, wherein a plurality of deflection patterns having deflection inclined surfaces are formed in the display region in at least one of the light-emitting surface of the light guide plate and an opposite surface to the light-emitting surface, and light control means for reducing light is provided at least part of at least one of the light-emitting surface of the light guide plate and a surface except the opposite surface to the light-emitting surface, the light being reflected toward the display region by the surface. 
         [0014]    In a surface illumination device according to one or more embodiments of the present invention, the light control means for reducing the light is provided at least part of at least one of the light-emitting surface of the light guide plate and the surface except the opposite surface to the light-emitting surface, the light being reflected toward the display region by the surface. Therefore, the light can be prevented from reaching the display region from an undesirable direction to shine the display region. Accordingly, the extra stray light is reduced, the flickering of the display region is hardly generated even if the seeing direction is changed or the instrument into which the surface illumination device is incorporated is inclined when the display region emits the light. 
         [0015]    In a surface illumination device according to one or more embodiments of the present invention, the light control means is a notch unit in which an angle is fixed such that the light incident to the light control means is transmitted toward an outside of the light guide plate. The light, which is reflected by certain surface of the light guide plate to reach the display region from the undesirable direction, can be transmitted to the outside from the notch unit. Accordingly, the light reaching the display unit from the undesirable direction can be reduced. 
         [0016]    In a surface illumination device according to one or more embodiments of the present invention, the light control means is a light-absorbing layer that absorbs the light incident to the light control means. The light, which is reflected by certain surface of the light guide plate to reach the display region from the undesirable direction, can be absorbed by the light-absorbing layer that is of the light control means. Accordingly, the light reaching the display unit from the undesirable direction can be reduced. 
         [0017]    In a surface illumination device according to one or more embodiments of the present invention, the light control means is a light scattering surface that scatters the light incident to the light control means. The light, which is reflected by certain surface of the light guide plate to reach the display region from the undesirable direction, can be scattered by the light scattering surface that is of the light control means. Accordingly, the light reaching the display unit from the undesirable direction can be reduced. 
         [0018]    In accordance with one or more embodiments of the present invention, a mobile phone that has transmission and reception functions, includes the surface illumination device in order to optically display certain shape. In one or more embodiments of the present invention, the surface illumination device according to one or more embodiments of the present invention is used in mobile phones such as the smartphone. Accordingly, the display such as the optically-displayed icon can be prevented from flickering. 
         [0019]    In accordance with one or more embodiments of the present invention, an information terminal that has an information processing function includes the surface illumination device according to one or more embodiments the present invention in order to optically display certain shape. In one or more embodiments of the present invention, the surface illumination device according to one or more embodiments of the present invention is used in information terminals such as a mobile computer, the tablet computer, an electronic diary, and an electronic dictionary. Accordingly, the display such as the optically-displayed icon can be prevented from flickering. 
         [0020]    The present invention includes variations that can be made by the combination of components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1(A)  is a plan view of a smartphone.  FIG. 1(B)  is a plan view of a surface illumination device incorporated in the smartphone in  FIG. 1(A) . 
           [0022]      FIG. 2(A)  is a schematic sectional view of the surface illumination device in  FIG. 1(B)  together with one enlarged deflection pattern.  FIG. 2(B)  is a plan view of a display unit (deflection pattern region) provided in a light guide plate. 
           [0023]      FIG. 3(A)  is a view illustrating light incident to the display unit in the surface illumination device in  FIG. 1(B) .  FIG. 3(B)  is a view illustrating a directional pattern of the light emitting from a light-emitting surface of a light guide plate when viewed from a direction perpendicular to the light-emitting surface. 
           [0024]      FIG. 4  is a view illustrating a problematic point of the surface illumination device in  FIG. 1(B) . 
           [0025]      FIG. 5  is a schematic plan view of a surface illumination device according to a first embodiment of the present invention. 
           [0026]      FIG. 6  is an explanatory view of action of the surface illumination device of the first embodiment. 
           [0027]      FIGS. 7(A) and 7(B)  are enlarged perspective views of a deflection pattern. 
           [0028]      FIG. 8  is a schematic plan view of a surface illumination device according to a second embodiment of the present invention. 
           [0029]      FIG. 9  is a schematic plan view of a surface illumination device according to a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF SYMBOLS 
       [0000]    
       
           11  smartphone 
           12  liquid crystal display screen 
           13  icon 
           16  light guide plate 
           16   a  light incident end face 
           16   b  side surface 
           16   c  light-emitting surface 
           17  light source 
           18  deflection pattern 
           19  display unit 
           21 ,  31 ,  41  surface illumination device 
           22  notch 
           32  light-absorbing layer 
           42  light scattering surface 
       
     
       DETAILED DESCRIPTION 
       [0044]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, but various design changes can be made without departing from the scope of the present invention. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. 
         [0045]    The surface illumination device according to one or more embodiments of the present invention is used in display of mobile devices such as a mobile phone, a tablet computer, and an electronic book reader. The case that the surface illumination device is used in a smartphone that is of the mobile phone will be described below. Because the smartphone is illustrated in  FIG. 1(A) , the smartphone is not further displayed. In the surface illumination device according to one or more embodiments of the present invention, because the conventional surface illumination device  15  is illustrated in  FIGS. 1(B) ,  2 (A), and  2 (B), the component identical to that of the conventional surface illumination device  15  is designated by the identical numeral, the overlapping description is omitted, and a point different from that of the conventional surface illumination device  15  is mainly be described. 
       First Embodiment 
       [0046]    A surface illumination device  21  according to a first embodiment of the present invention will be described.  FIG. 5  is a schematic plan view of the surface illumination device  21  of the first embodiment. The first embodiment focuses on light Lb, which is incident to the light guide plate  16  from the light source  17  and reaches the display unit  19  (the display region) after being totally reflected by the side surface  16   b  of the light guide plate  16  in the conventional surface illumination device  15  (see  FIG. 3(A) ). 
         [0047]    In the surface illumination device  21  of the first embodiment, a notch  22  (the light control means) is provided in a region, where the light Lb is totally reflected by the side surface  16   b,  so as to transmit the incident light Lb. That is, the notch  22  includes a notch surface  22   a  that is irradiated with the incident light Lb and a notch surface  22   b  that is hardly irradiated with the light Lb. The notch surface  22   a  is formed at an angle such that the incident light Lb is substantially transmitted without the total reflection. For example, the angle of the notch surface  22   a  is fixed so as to be substantially orthogonal to a direction in which the light Lb incident from the side of the light source  17  has a maximum intensity. The angle of the notch surface  22   b  is fixed such that the light Lb transmitted through the notch surface  22   a  is not incident to the light guide plate  16  again, and such that other pieces of light are not totally reflected toward the display unit  19 . For example, the notch surface  22   b  may be fixed so as to be substantially parallel to the direction in which the light Lb incident from the light source  17  has the maximum intensity. 
         [0048]    In the surface illumination device  21 , the light Lb that is totally reflected by the side surface  16   b  of the light guide plate  16  to reach the display unit  19  in the conventional example leaks to the outside of the light guide plate  16  from the notch  22  to hardly reach the display unit  19 . As illustrated in  FIG. 6 , the light having the high intensity only on the front side (the light having the directional pattern Cb in  FIG. 3(B)  is eliminated) is emitted from the light-emitting surface  16   c  of the light guide plate  16 . As a result, the icon  13  of the smartphone  11  is not seen from the oblique direction but seen from the front. Therefore, even if the user vertically inclines the smartphone  11  or vertically moves eyes or a head, the icon  13  is not seen while flickering, but display quality of the icon  13  is improved. 
         [0049]    The notch  22  is provided only in part of the side surface  16   b  of the light guide plate  16 . However, as illustrated in  FIG. 5 , even if the light is totally reflected by a place except the notch  22 , the light is reflected toward the direction deviated from the display unit  19 , but the light does not shine the display unit  19 . Therefore, no problem is generated. 
         [0050]    The deflection pattern  18  constituting the display unit  19  is generally formed into a triangular shape, particularly a right triangular shape as illustrated in  FIG. 7(A) . Alternatively, the deflection pattern  18  may be formed into a shape in which a deflection reflecting surface  18   a  is curved as illustrated in  FIG. 7(B) . The notch  22  may be provided only in one of the side surfaces  16   b.    
       Second Embodiment 
       [0051]    A surface illumination device  31  according to a second embodiment of the present invention will be described.  FIG. 8  is a schematic plan view of the surface illumination device  31  of the second embodiment. 
         [0052]    In the surface illumination device  31  of the second embodiment, a light-absorbing layer  32  is provided in the region, where the light Lb reaching the display unit  19  is totally reflected by the side surface  16   b,  by applying a black paint or attaching a black adhesive tape. 
         [0053]    In the surface illumination device  31 , the light Lb that is totally reflected by the side surface  16   b  of the light guide plate  16  to reach the display unit  19  in the conventional example is absorbed by the light-absorbing layer  32  and hardly totally reflected by the side surface  16   b.  In the second embodiment, the light having the high intensity is emitted only onto the front side from the light-emitting surface  16   c.  The icon  13  of the smartphone  11  is not seen from the oblique direction but seen from the front. Therefore, even if the user vertically inclines the smartphone  11  or vertically moves eyes or a head, the icon  13  is not seen while flickering, but the display quality of the icon  13  is improved. 
         [0054]    The light-absorbing layer  32  may be provided only in one of the side surfaces  16   b.    
       Third Embodiment 
       [0055]    A surface illumination device  41  according to a third embodiment of the present invention will be described.  FIG. 9  is a schematic plan view of the surface illumination device  41  of the third embodiment. 
         [0056]    In the surface illumination device  41  of the third embodiment, a light scattering surface  42  is processed in the region where the light Lb reaching the display unit  19  is totally reflected by the side surface  16   b.  For example, the region of the side surface  16   b  is coarsely formed, or formed into a random prism shape. 
         [0057]    In the surface illumination device  41 , the light Lb that is totally reflected by the side surface  16   b  of the light guide plate  16  to reach the display unit  19  in the conventional example is scattered by the light scattering surface  42 , but the light having the high intensity is not reflected in a specific direction. In the third embodiment, the light having the high intensity is emitted only onto the front side from the light-emitting surface  16   c.  The icon  13  of the smartphone  11  is not seen from the oblique direction but seen from the front. Therefore, even if the user vertically inclines the smartphone  11  or vertically moves eyes or a head, the icon  13  is not seen while flickering, but the display quality of the icon  13  is improved. 
         [0058]    The light scattering surface  42  may be provided only in one of the side surfaces  16   b.    
         [0059]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.