Abstract:
This luminous flux control member has: an incidence surface through which light emitted from a light-emitting element enters; an emission surface through which the light entering from the incidence surface is emitted to the outside; and multiple ridges that are formed on the back side so as to surround the central axis (CA) and that have a substantially triangular cross-sectional shape. Each of the multiple ridges has a first reflecting surface, a second reflecting surface, and a ridge line which is the line of intersection of the first reflecting surface and the second reflecting surface. An imaginary line containing the ridge lines intersects the central axis (CA) at a position closer to the front side than the ridge lines.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a light flux controlling member configured to control the distribution of light emitted from a light emitting element. Further, the present invention relates to a light emitting device including the light flux controlling member, a surface light source device including the light emitting device, and a display apparatus including the surface light source device. 
       BACKGROUND ART 
       [0002]    Some transmission type image display apparatuses such as liquid crystal display apparatuses employ a direct-type surface light source device as a backlight. In recent years, a direct-type surface light source device including a plurality of light emitting elements has been increasingly used as a light source. 
         [0003]    A direct-type surface light source device has, for example, a substrate, a plurality of light emitting elements, a plurality of light flux controlling members (lenses) and a light diffusion member. The plurality of light emitting elements are disposed in a matrix on the substrate. Over each light emitting element, the light flux controlling member is disposed for expanding light emitted from each light emitting element in the surface directions of the substrate. The light output from the light flux controlling member is diffused by the light diffusion member, and planarly illuminates a member to be irradiated (e.g. a liquid crystal panel). 
         [0004]      FIGS. 1A to 1C  illustrate a configuration of a conventional light flux controlling member.  FIG. 1A  is a perspective view from the rear side,  FIG. 1B  is a cross-sectional perspective view from the rear side, and  FIG. 1C  is a cross-sectional view. In  FIGS. 1A and 1B , legs formed on the rear side are not illustrated. As illustrated in  FIGS. 1A to 1C , conventional light flux controlling member  20  includes incidence surface  22  on which light emitted from a light emitting element is incident and emission surface  24  for outputting the light entered from incidence surface  22  toward the outside. Incidence surface  22  is a surface with a recessed shape relative to the light emitting element and formed so as to face the light emitting surface of the light emitting element. 
         [0005]      FIGS. 2A to 2C  are illustrations of optical paths in light flux controlling member  20 .  FIG. 2A  is an illustration of an optical path of a beam with emission angle 30°,  FIG. 2B  is an illustration of an optical path of a beam with emission angle 40°, and  FIG. 2C  is an illustration of an optical path of a beam with emission angle 50°. As used herein, “emission angle” ( 0  in  FIG. 2A ) means an angle of a beam relative to optical axis LA of light emitting element  10 . Also in  FIGS. 2A to 2C , legs formed on the rear side are not illustrated. 
         [0006]    As illustrated in  FIGS. 2A to 2C , the light emitted from light emitting element  10  enters the inside of light flux controlling member  20  from incidence surface  22 . The light entered light flux controlling member  20  reaches emission surface  24 , and is output toward the outside from emission surface  24  (solid arrow). At this time, the light is refracted according to the shape of emission surface  24 , so that the traveling direction of the light can be controlled. On the other hand, part of the light reached emission surface  24  is reflected by emission surface  24  (Fresnel reflection) and reaches rear surface  26  facing the substrate on which light emitting element  10  is mounted (dashed arrow). When the light reached rear surface  26  is reflected by rear surface  26 , excessive light travels in the direction directly above light flux controlling member  20  and therefore, luminance unevenness occurs. When the light reached rear surface  26  is output from rear surface  26 , the light is absorbed into the substrate and therefore, the loss of light is large. 
         [0007]    It is undesirable that the light reflected by emission surface  24  travel in the direction directly above light flux controlling member  20  or be absorbed into the substrate. PTL 1 proposes a light flux controlling member that can solve the above problems. 
         [0008]      FIGS. 3A to 3C  illustrate a configuration of a light flux controlling member disclosed in PTL 1.  FIG. 3A  is a perspective view from the rear side,  FIG. 3B  is a cross-sectional perspective view from the rear side, and  FIG. 3C  is a cross-sectional view. In  FIGS. 3A and 3B , legs formed on the rear side are not illustrated. As illustrated in  FIGS. 3A to 3C , in light flux controlling member  30  disclosed in PTL 1, annular inclining surface  32  is formed in rear surface  26 . Inclining surface  32  is rotationally symmetric (circularly symmetric) about central axis CA of light flux controlling member  30 , and inclined at a predetermined angle (e.g. 45°) relative to central axis CA. 
         [0009]      FIGS. 4A to 4C  are illustrations of optical paths in light flux controlling member  30 .  FIG. 4A  is an illustration of an optical path of a beam with emission angle 30°,  FIG. 4B  is an illustration of an optical path of a beam with emission angle 40°, and  FIG. 4C  is an illustration of an optical path of a beam with emission angle 50°. Also in  FIGS. 4A to 4C , legs formed on the rear side are not illustrated. As illustrated in  FIGS. 4A to 4C , light reflected by emission surface  24  reaches inclining surface  32  in light flux controlling member  30 . Then, part of the light reached inclining surface  32  is reflected by inclining surface  32  and travels in a lateral direction (see  FIGS. 4A and 4B ). 
         [0010]    In this way, in light flux controlling member  30  disclosed in PTL 1, the light reflected by emission surface  24  does not easily travel in the direction directly above light flux controlling member  30  or is not easily absorbed into the substrate. Therefore, a light emitting device including light flux controlling member  30  disclosed in PTL 1 can radiate light more efficiently and uniformly than a light emitting device including conventional light flux controlling member  20 . 
       CITATION LIST 
     Patent Literature 
       [0011]    PTL 1: Japanese Patent Application Laid-Open No. 2009-43628 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0012]    As illustrated in  FIG. 4C , even in light flux controlling member  30  disclosed in PTL 1, when a beam has a large emission angle, part of light reflected by emission surface  24  may reach the substrate under light flux controlling member  30  after passing through inclining surface  32  according to the angle of inclining surface  32 . The light reached the substrate under light flux controlling member  30  in this way may be reflected by the surface of the substrate to travel in the direction directly above light flux controlling member  30 , or may be absorbed into the substrate. From the perspective of energy saving, it is preferable to reduce the amount of light passing through inclining surface  32  as much as possible. 
         [0013]    An object of the present invention is to provide a light flux controlling member configured to control the distribution of light emitted from a light emitting element, the light flux controlling member being capable of using light reflected by an emission surface more efficiently while preventing the occurrence of luminance unevenness. 
         [0014]    Another object of the present invention is to provide a light emitting device including the light flux controlling member, a surface light source device including the light emitting device, and a display apparatus including the surface light source device. 
       Solution to Problem 
       [0015]    A light flux controlling member configured to control the distribution of light emitted from a light emitting element, the light flux controlling member includes: an incidence surface formed on a rear side of the light flux controlling member so as to intersect a central axis of the light flux controlling member, the incidence surface being configured such that light emitted from the light emitting element is incident on the incidence surface; an emission surface formed on a front side of the light flux controlling member so as to intersect the central axis, the emission surface being configured to output light entered from the incidence surface toward outside; and a plurality of linear protrusions each having a cross-section that is substantially triangle-shaped, the linear protrusions being formed to surround the central axis; wherein each of the plurality of linear protrusions includes a first reflection surface, a second reflection surface, and a ridge line that is an intersection line of the first reflection surface and the second reflection surface, the plurality of linear protrusions are disposed rotationally symmetric about the central axis, and a virtual line including the ridge line intersects the central axis at a position which is farther into a front side area of the light flux controlling member than the ridge line. 
         [0016]    A light emitting device of the present invention includes a light emitting element and the light flux controlling member of the present invention, wherein the light flux controlling member is disposed such that the central axis thereof coincides with the optical axis of the light emitting element. 
         [0017]    A surface light source device of the present invention includes the light emitting device of the present invention and a light diffusion member which is configured to diffuse and transmit the light emitted from the light emitting device at the same time. 
         [0018]    A display apparatus of the present invention includes the surface light source device of the present invention and a display member to which light emitted from the surface light source devices is radiated. 
       Advantageous Effects of Invention 
       [0019]    A light emitting device including a light flux controlling member of the present invention can radiate light more efficiently and uniformly than a light emitting device including a conventional light flux controlling member. Therefore, a surface light source device and display apparatus of the present invention have higher light use efficiency and less luminance unevenness occurrence than conventional ones. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIGS. 1A to 1C  illustrate a configuration of a conventional light flux controlling member; 
           [0021]      FIGS. 2A to 2C  are illustrations of optical paths in the light flux controlling member illustrated in  FIGS. 1A to 1C ; 
           [0022]      FIGS. 3A to 3C  illustrate a configuration of a light flux controlling member disclosed in PTL 1; 
           [0023]      FIGS. 4A to 4C  are illustrations of optical paths in the light flux controlling member illustrated in  FIGS. 3A to 3C ; 
           [0024]      FIGS. 5A and 5B  illustrate a configuration of a surface light source device according to Embodiment 1; 
           [0025]      FIGS. 6A and 6B  are cross-sectional illustrations illustrating the configuration of the surface light source device according to Embodiment 1; 
           [0026]      FIG. 7  is a partially enlarged cross-sectional view of an enlarged part of  FIG. 6B ; 
           [0027]      FIGS. 8A and 8B  illustrate a configuration of a light flux controlling member according to Embodiment 1; 
           [0028]      FIGS. 9A to 9D  illustrate the configuration of the light flux controlling member according to Embodiment 1; 
           [0029]      FIG. 10  is a cross-sectional view of the light flux controlling member according to Embodiment 1 to explain the directions of ridge lines; 
           [0030]      FIGS. 11A to 11C  are illustrations of optical paths in the light flux controlling member according to Embodiment 1; 
           [0031]      FIG. 12  is a graph illustrating illuminance distributions on the surfaces of substrates under the light flux controlling members; 
           [0032]      FIG. 13  is a graph illustrating average illuminances in regions under the light flux controlling members; 
           [0033]      FIG. 14  is a graph illustrating incident light fluxes in the regions under the light flux controlling members; 
           [0034]      FIGS. 15A and 15B  are bottom illustrations of modifications of the light flux controlling member according to Embodiment 1; 
           [0035]      FIGS. 16A and 16B  illustrate a configuration of a light flux controlling member according to Embodiment 2; 
           [0036]      FIGS. 17A to 17D  illustrate the configuration of the light flux controlling member according to Embodiment 2; 
           [0037]      FIGS. 18A and 18B  illustrate a modification of the light flux controlling member according to Embodiment 2; 
           [0038]      FIGS. 19A and 19B  illustrate another modification of the light flux controlling member according to Embodiment 2; and 
           [0039]      FIG. 20  is a cross-sectional view of a light flux controlling member according to Embodiment 3. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, as representative examples of surface light source devices of the present invention, surface light source devices suitable for backlights of liquid crystal display apparatuses or the like will be described. These surface light source devices may be used as display apparatuses in combination with members to be irradiated (e.g. liquid crystal panels) to which light from the surface light source devices is radiated. 
       Embodiment 1 
     Configurations of Surface Light Source Device and Light Emitting Device 
       [0041]      FIGS. 5A to 7  illustrate a configuration of a surface light source device according to Embodiment 1.  FIG. 5A  is a plan view, and  FIG. 5B  is a front view.  FIG. 6A  is a cross-sectional view taken along line A-A shown in  FIG. 5B , and  FIG. 6B  is a cross-sectional view taken along line B-B shown in  FIG. 5A .  FIG. 7  is a partially enlarged cross-sectional view of an enlarged part of  FIG. 6B . 
         [0042]    As illustrated in  FIGS. 5A to 6B , surface light source device  100  according to Embodiment 1 includes casing  110 , a plurality of light emitting devices  200 , and light diffusion member  120 . Light emitting devices  200  are disposed in a matrix on bottom plate  112  of casing  110 . The inner surface of bottom plate  112  functions as a diffusion and reflection surface. Top plate  114  of casing  110  has an opening. Light diffusion member  120  is disposed so as to fill the opening, and functions as a light emitting surface. The size of the light emitting surface is, for example but not limited to, about 700 mm in length and about 400 mm in width. 
         [0043]    As illustrated in  FIG. 7 , each of light emitting devices  200  is fixed to each of substrates  210 . Each of substrates  210  is fixed on bottom plate  112  of casing  110  at each predetermined position. Each of light emitting devices  200  includes light emitting element  220  and light flux controlling member  300 . 
         [0044]    Light emitting element  220  is a light source of surface light source device  100 , and mounted on substrate  210 . Light emitting element  220  is a light-emitting diode (LED) such as a white light emitting diode. 
         [0045]    Light flux controlling member  300  is a diffusion lens configured to control the distribution of light emitted from light emitting element  220 , and fixed on substrate  210 . Light flux controlling member  300  is disposed over light emitting element  220  such that central axis CA thereof coincides with optical axis LA of light emitting element  220  (see  FIG. 10 ). Later-described incidence surface  320  and emission surface  330  of light flux controlling member  300  are both rotationally symmetric (circularly symmetric), and rotation axes thereof coincide with each other. The axes of incidence surface  320  and emission surface  330  are hereinafter referred to as “central axis CA of the light flux controlling member.” Further, “optical axis LA of the light emitting element” means a center beam of a three-dimensional light flux from light emitting element  220 . A gap to release generated heat from light emitting element  220  to the outside is formed between substrate  210  on which light emitting element  220  is mounted and rear surface  340  of light flux controlling member  300 . 
         [0046]    Light flux controlling member  300  is formed by integral molding. The material of light flux controlling member  300  is not particularly limited as long as light with desired wavelength can pass through. For example, the material of light flux controlling member  300  is a light-transmissive resin such as polymethylmethacrylate (PMMA), polycarbonate (PC) or epoxy resin (EP), or glass. 
         [0047]    A main feature of surface light source device  100  according to the present embodiment lies in a configuration of light flux controlling member  300 . Therefore, light flux controlling member  300  will be described in detail later. 
         [0048]    Light diffusion member  120  is a plate-shaped member having light diffusivity, and configured to diffuse and transmit the light emitted from light emitting device  200  at the same time. Normally, the size of light diffusion member  120  is substantially the same as the size of a member to be irradiated such as a liquid crystal panel. For example, light diffusion member  120  is formed of a light-transmissive resin such as polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS) or styrene-methylmethacrylate copolymer resin (MS). To confer light diffusivity, fine irregularities are formed on the surface of light diffusion member  120 , or light diffusion elements such as beads are dispersed in light diffusion member  120 . 
         [0049]    In surface light source device  100  according to the present embodiment, light emitted from each light emitting element  220  is expanded by light flux controlling member  300  to illuminate a broad region of light diffusion member  120 . Further, the light output from each light flux controlling member  300  is diffused by light diffusion member  120 . As a result, surface light source device  100  according to the present embodiment can uniformly illuminate a planar member to be irradiated (e.g. liquid crystal panel). 
       (Configuration of Light Flux Controlling Member) 
       [0050]      FIGS. 8A to 9D  illustrate a configuration of light flux controlling member  300  according to Embodiment 1.  FIG. 8A  is a perspective view from the rear side, and  FIG. 8B  is a cross-sectional perspective view from the rear side.  FIG. 9A  is a plan view,  FIG. 9B  is a front view,  FIG. 9C  is a bottom view and  FIG. 9D  is a cross-sectional view taken along line C-C shown in  FIG. 9A . In  FIGS. 8A and 8B , legs  370  formed on the rear side are not illustrated. 
         [0051]    As illustrated in  FIGS. 8A to 9D , light flux controlling member  300  includes recess  310 , incidence surface  320 , emission surface  330 , rear surface  340 , reflection portion  350 , flange  360  and a plurality of legs  370 . 
         [0052]    Recess  310  is formed in a central portion of the rear side (light emitting element  220  side) of light flux controlling member  300 . The inner surface of recess  310  functions as incidence surface  320 . Incidence surface  320  allows most of the light emitted from light emitting element  220  to enter the inside of light flux controlling member  300  while controlling the traveling direction of the light. Incidence surface  320  intersects central axis CA of light flux controlling member  300  and is rotationally symmetric (circularly symmetric) about central axis CA. 
         [0053]    Emission surface  330  is formed on the front side (light diffusion member  120  side) of light flux controlling member  300  so as to protrude from flange  360 . Emission surface  330  is configured to output the light entered light flux controlling member  300  while controlling the traveling direction of the light. Emission surface  330  intersects central axis CA and is rotationally symmetric (circularly symmetric) about central axis CA. 
         [0054]    Emission surface  330  includes first emission surface  330   a  located in a predetermined area about central axis CA, second emission surface  330   b  formed around and continued from first emission surface  330   a , and third emission surface  330   c  connecting second emission surface  330   b  with flange 360  (see  FIG. 9D ). First emission surface  330   a  is a smoothly curved surface protruding to the rear side (light emitting element  220  side). The shape of first emission surface  330   a  is a concave shape such that a part of spherical surface is cut off. Second emission surface  330   b  is a smoothly curved surface protruding to the front side (light diffusion member  120  side) located around first emission surface  330   a . The shape of second emission surface  330   b  is a toric convex shape. Third emission surface  330   c  is a curved surface located around second emission surface  330   b . In the cross-section illustrated in  FIG. 9D , the cross-sectional shape of third emission surface  330   c  may be linear or curved. 
         [0055]    Rear surface  340  is a plane located on the rear side and extending radially from the opening edge of recess  310 . Rear surface  340  allows light emitted from light emitting element  220  but not entered from incidence surface  320  to enter light flux controlling member  300 . 
         [0056]    Reflection portion  350  is disposed in a ring form on the rear side (light emitting element  220  side) of light flux controlling member  300  so as to surround the opening of recess  310 . A plurality of linear protrusions  352  are formed in reflection portion  350 . Linear protrusions  352  are formed such that a cross-section of each linear protrusion vertical to later-described ridge line  352   c  is substantially triangle-shaped, and that the linear protrusions are formed rotationally symmetric about central axis CA (when the number of the linear protrusions is n, they are n-fold symmetrical). Each linear protrusion  352  includes planar first reflection surface  352   a , planar second reflection surface  352   b , and ridge line  352   c  that is an intersection line of first reflection surface  352   a  and second reflection surface  352   b . Linear protrusion  352  functions like a total reflection prism. As illustrated in  FIG. 10 , a virtual line including ridge line  352   c  intersects central axis CA at a position which is farther into the front side area (light diffusion member  120  side) of the light flux controlling member than ridge line  352   c . That is, each linear protrusion  352  is inclined at a predetermined angle (e.g. 45°) relative to central axis CA such that the front end (light diffusion member  120  side) of linear protrusion  352  is closer to central axis CA than the rear end (light emitting element  220  side) of linear protrusion  352  is. 
         [0057]    Reflection portion  350  will be described from a different perspective. A ring formed groove about central axis CA is formed in rear surface  340 . The cross-sectional shape of the ring formed groove in a cross-section including central axis CA is substantially V-shaped. Of the two surfaces forming the V-shape, the inner surface is substantially parallel to optical axis LA of light emitting element  220 , and the outer surface is inclined at a predetermined angle (e.g. 45°) relative to optical axis LA of light emitting element  220 . On the outer inclining surface, linear protrusions  352  (total reflection prisms) are formed. 
         [0058]    Reflection portion  350  reflects light, which is reflected by emission surface  330  and travels to rear surface  340 , in a lateral direction (radially outside relative to central axis CA). The light reached reflection portion  350  is reflected sequentially by two surfaces (first reflection surface  352   a  and second reflection surface  352   b ) of any one of linear protrusions  352  and travels in a lateral direction. The light reflected by reflection portion  350  is output from flange  360 , for example. 
         [0059]    Reflection portion  350  is preferably located such that linear protrusions  352  are formed in a region where a large amount of light reflected by emission surface  330  reaches, but the location is not limited to thereto. Although the arrival position of the light reflected by emission surface  330  varies according to various factors such as the shape of emission surface  330 , in light flux controlling member  300  according to the present embodiment illustrated in  FIG. 9D , most of the light Fresnel-reflected by emission surface  330  after entered from incidence surface  320  reaches a predetermined annular region on rear surface  340  (see  FIGS. 11A to 11C ). In the case of light flux controlling member  20  (with the outer diameter of rear surface of 15.5 mm) used in a later-described simulation of illuminance distribution in a region facing rear surface  340  on substrate  210 , the highest illuminance value is obtained in a region 5 to 6 mm apart from central axis CA (see  FIG. 12 ). It can be deduced that the region is where a substantial amount of light Fresnel-reflected by emission surface  24  after entered from incidence surface  22  is likely to reach. Therefore, it is preferable to form a plurality of linear protrusions  352  at least in the region 5 to 6 mm apart from central axis CA in light flux controlling member  20 . 
         [0060]    Flange  360  is located between the outer peripheral portion of emission surface  330  and the outer peripheral portion of rear surface  340 , and protruding radially outside. The shape of flange  360  is a substantially ring form. Although flange  360  is not an essential component, handling and alignment are easier with flange  360  formed. The thickness of flange  360  is not limited, and can be determined in view of the required area of emission surface  330 , formability of flange  360 , or the like. 
         [0061]    A plurality of legs  370  are substantially cylindrical members protruding from rear surface  340 . Legs  370  hold light flux controlling member  300  at an appropriate position relative to light emitting element  220 . 
         [0062]      FIGS. 11A to 11C  are illustrations of optical paths in light flux controlling member  300 .  FIG. 11A  is an illustration of an optical path of a beam with emission angle 30°,  FIG. 11  is an illustration of an optical path of a beam with emission angle 40°, and  FIG. 11C  is an illustration of an optical path of a beam with emission angle 50°. In  FIGS. 11A to 11C , legs  370  are not illustrated. As illustrated in  FIGS. 11A to 11C , light reflected by emission surface  330  reaches reflection portion  350  in light flux controlling member  300 . The light reached reflection portion  350  is reflected sequentially by first reflection surface  352   a  and second reflection surface  352   b  of linear protrusion  352  and travels in a lateral direction. 
         [0063]    As can be seen from light flux controlling member  30  disclosed in PTL 1, when inclining surface  32  is formed in rear surface  26 , the direction of light Fresnel-reflected by emission surface  24  can be changed in a lateral direction, so that light use efficiency can be increased. However, when a beam has a large emission angle, part of light reflected by emission surface  24  may reach the substrate under light flux controlling member  30  after passing through inclining surface  32  (see  FIG. 4C ), and further improvement may be needed. In light flux controlling member  300  according to the present embodiment, linear protrusions  352  (total reflection prisms) are formed on the inclining surface, so that a beam having a large emission angle which is Fresnel-reflected by emission surface  330  can be reflected in a lateral direction (see  FIG. 11C ). Therefore, in light flux controlling member  300  according to the present embodiment, more light reflected by emission surface  330  travels in lateral directions, so that the loss of light caused by light reflected by emission surface  330  being reflected by or absorbed into substrate  210  can be limited. 
         [0000]    (Simulation of Illuminance Distribution in Region under Light Flux Controlling Member) 
         [0064]    For light flux controlling member  300  according to Embodiment 1 illustrated in  FIGS. 8A to 9D , the illuminance distribution in a region under the light flux controlling member was simulated. For comparison, the illuminance distribution was simulated also for conventional light flux controlling member  20  illustrated in  FIGS. 1A to 1C  and light flux controlling member  30  disclosed in PTL 1 illustrated in  FIGS. 3A to 3C . 
         [0065]    In the simulation, the illuminance distribution on the surface of substrate  210  when light emitting element  220  and light flux controlling member  300  (or  20  or  30 ) are disposed on substrate  210  illustrated in  FIG. 7  was measured. Light reached the surface of substrate  210  was set to be not reflected but absorbed. Three light flux controlling members  300 ,  20  and  30  used for simulations are different from each other only in that whether or not they have inclining surface  32  or reflection portion  350  on the rear sides. Parameters for light flux controlling members  300 ,  20  and  30  were set as follows: 
       (Common Parameters) 
       [0066]    Outer diameter of emission surface: 14.778 mm 
         [0067]    Outer diameter of rear surface: 15.5 mm 
         [0068]    Opening diameter of recess: 3.53 mm 
         [0069]    Height from surface of substrate to rear surface: 1.1 mm 
         [0070]    Height from surface of substrate to highest point of emission surface: 5.867 mm 
         [0071]    (Parameters Only for Light Flux Controlling Member  30 ) 
         [0072]    Outer diameter of inclining surface: 6.057 mm 
         [0073]    Angle of inclining surface: 45° relative to optical axis 
         [0074]    (Parameters Only for Light Flux Controlling Member  300 ) 
         [0075]    Outer diameter of reflection portion: 6.057 mm 
         [0076]    Angle of ridge line: 45° relative to optical axis 
         [0077]      FIG. 12  is a graph illustrating the illuminance distribution on the surface of substrates under the light flux controlling member. The abscissa represents the distance (mm) from the central axis of the light flux controlling member on the line intersecting the central axis of the light flux controlling member. The ordinate represents the illuminance (lx) at different points. The result of light flux controlling member  20  having no inclining surface is shown by thin dashed line, the result of light flux controlling member  30  not having a plurality of linear protrusions but having an inclining surface is shown by thin solid line, and the result of light flux controlling member  300  having a plurality of linear protrusions is shown by thick solid line. As shown in the graph, the illuminance in the region 4.5 to 6.5 mm apart from the central axis is different among the light flux controlling members. That is, the illuminance in the region under light flux controlling member  30  having the inclining surface (see  FIGS. 3A to 3C ) is lower than the illuminance in the region under light flux controlling member  20  having no inclining surface (see  FIGS. 1A to 1C ). Further, the illuminance in the region under light flux controlling member  300  having the linear protrusions (see  FIGS. 8A to 9D ) is lower than the illuminance in the region under light flux controlling member  30  having the inclining surface (but not having a plurality of linear protrusions) (see  FIGS. 3A to 3C ). 
         [0078]      FIG. 13  is a graph illustrating average illuminance (lx) in the region under light flux controlling member (circular region with a diameter of 19 mm) On the abscissa, “A” represents light flux controlling member  20  having no inclining surface, “B” represents light flux controlling member  30  not having a plurality of linear protrusions but having the inclining surface, and “C” represents light flux controlling member  300  having the linear protrusions. This graph also shows that light flux controlling member  300  having the linear protrusions (see  FIGS. 8A to 9D ) exhibits low illuminance in the region under the flux controlling member compared to flux controlling member  20  having no inclining surface (see  FIGS. 1A to 1C ) and flux controlling member  30  having the inclining surface (but not having a plurality of linear protrusions) (see  FIGS. 3A to 3C ). 
         [0079]      FIG. 14  is a graph illustrating incident light flux (lm) in the region under the light flux controlling member (circular region with diameter 19 mm) Also on the abscissa of this graph, “A” represents light flux controlling member  20  having no inclining surface, “B” represents light flux controlling member  30  not having a plurality of linear protrusions but having the inclining surface, and “C” represents light flux controlling member  300  having the linear protrusions. The amount of light flux from a light emitting element is 1 lm. This graph also shows that light flux controlling member  300  having the linear protrusions (see  FIGS. 8A to 9D ) exhibits a small amount of light flux reached the region under the flux controlling member compared to flux controlling member  20  having no inclining surface (see  FIGS. 1A to 1C ) and flux controlling member  30  having the inclining surface (but not having a plurality of linear protrusions) (see  FIGS. 3A to 3C ). 
         [0080]    As described above, in light flux controlling member  300  according to the present embodiment, the light reflected by emission surface  330  does not easily travel in the direction directly above light flux controlling member  300  or is not easily absorbed into substrate  210 . Therefore, light emitting device  200  according to the present invention can radiate light more efficiently and uniformly than light emitting devices including the conventional light flux controlling member. 
         [0081]    In the present embodiment, light flux controlling member  300  in which rear surface  340  is a flat surface is described, but a part or all of rear surface  340  may be a light scattering surface. For example, as illustrated in  FIGS. 15A and 15B , a part of rear surface  340  may be light scattering surface  342  (the region indicated by hatching). In  FIG. 15A , the region inside legs  370  is roughened. In  FIG. 15B , the region inside reflection portion  350  is roughened. When a part or all of rear surface  340  is a light scattering surface, luminance unevenness caused by light entered from rear surfaces  340  being gathered in an unintended direction can be prevented. 
         [0082]    To obtain such an effect, it is preferable that a region of rear surface  340  where light from light emitting element  220  may directly reach be a light scattering surface. The size of the region varies according to the distance between light emitting element  220  and rear surface  340 , the size of light emitting element  220 , the size of the opening of recess  310 , or the like. Therefore, the region to be a light scattering surface may be appropriately set according to these parameters. 
       Embodiment 2 
     Configurations of Surface Light Source Device and Light Emitting Device 
       [0083]    A surface light source device and light emitting device according to Embodiment 2 differ from surface light source device  100  and light emitting device  200  according to Embodiment 1 illustrated in  FIGS. 5A to 7  in that the former include light flux controlling member  400  according to Embodiment 2 instead of light flux controlling member  300  according to Embodiment 1. Accordingly, only light flux controlling member  400  according to Embodiment 2 will be described in the present embodiment. 
       (Configuration of Light Flux Controlling Member) 
       [0084]      FIGS. 16A to 17D  illustrate a configuration of light flux controlling member  400  according to Embodiment 2.  FIG. 16A  is a perspective view from the rear side, and  FIG. 16B  is a cross-sectional perspective view from the rear side.  FIG. 17A  is a plan view,  FIG. 17B  is a front view,  FIG. 17C  is a bottom view and  FIG. 17D  is a cross-sectional view taken along line D-D shown in  FIG. 17A . In  FIGS. 16A and 16B , legs  370  formed on the rear side are not illustrated. 
         [0085]    As illustrated in  FIGS. 16A to 17D , light flux controlling member  400  includes recess  310 , incidence surface  320 , emission surface  330 , first rear surface  440   a , second rear surface  440   b , reflection portion  450 , flange  360  and a plurality of legs  370 . Elements that overlap with those of light flux controlling member  300  illustrated in  FIGS. 8A to 9D  are provided with symbols that are the same as those in  FIGS. 8A to 9D , and a description thereof will be omitted. 
         [0086]    In light flux controlling member  400  according to Embodiment 2, reflection portion  450  is formed lower (substrate  210  side) than the opening of recess  310 . Hence, on the rear side of light flux controlling member  400 , first rear surface  440   a  that is a plane extending from the opening edge of recess  310  to the upper end of reflection portion  450 , and second rear surface  440   b  that is a plane extending radially from the lower end of reflection portion  450  are formed. First rear surface  440   a  allows light emitted from light emitting element  220  but not entered from incidence surface  320  to enter light flux controlling member  400 . 
         [0087]    (Effect) 
         [0088]    Light flux controlling member  400  according to Embodiment 2 has the same effect as light flux controlling member  300  according to Embodiment 1. In light flux controlling member  300  according to Embodiment 1, light entered from incidence surface  320  at a large angle relative to optical axis LA may be reflected by reflection portion  350  in an unintended direction after reaching reflection portion  350 . On the other hand, in light flux controlling member  400  according to Embodiment 2, reflection portion  450  is formed lower than the opening of recess  310 , so that such unintended reflections do not occur. 
         [0089]    In light flux controlling member  400  according to the present embodiment, the size of the region accepting reflected light from emission surface  330  can be controlled by adjusting the parameters of reflection portion  450  (e.g. the size and inclination of first reflection surface  352   a  and second reflection surface  352   b , and the length and inclination of ridge line  352   c ). For example, as illustrated in  FIGS. 18A and 18B , the area of second rear surface  440   b  may be smaller, or the intervals between ridge lines  352   c  in reflection portion  450  may be longer. Further, as illustrated in  FIGS. 19A and 19B , the area of reflection portion may be larger by not forming second rear surface  440   b . In  FIGS. 18A to 19B , legs  370  formed on the rear side are not illustrated. 
         [0090]    In light flux controlling member  300  and  400  according to the present embodiment, each ridge line  352   c  may be formed by chamfering the ridge formed by two reflection surfaces  352   a  and  352   b  intersecting each other. 
         [0091]    Further, in the mode such as light flux controlling member  400  according to Embodiment 2 in which reflection portion  450  is formed lower (substrate  210  side) than the opening of recess  310 , light flux can be controlled more efficiently by expanding the area of emission surface  330  by forming thinner flange  360  with due considerations of handling and formability. 
       Embodiment 3 
     Configurations of Surface Light Source Device and Light Emitting Device 
       [0092]    A surface light source device and light emitting device according to Embodiment 3 differ from surface light source device  100  and light emitting device  200  according to Embodiment 1 illustrated in  FIGS. 5A to 7  in that the former include light flux controlling member  500  according to Embodiment 3 instead of light flux controlling member  300  according to Embodiment 1. Accordingly, only light flux controlling member  500  according to Embodiment 3 will be described in the present embodiment. 
       (Configuration of Light Flux Controlling Member) 
       [0093]      FIG. 20  is a cross-sectional view of light flux controlling member  500  according to Embodiment 3. 
         [0094]    As illustrated in  FIG. 20 , light flux controlling member  500  includes recess  310 , incidence surface  320 , emission surface  330 , rear surface  340 , reflection portion  350 , flange  560  and a plurality of legs  370 . Elements that overlap with those of light flux controlling member  300  illustrated in  FIGS. 8A to 9D  are provided with symbols that are the same as those in  FIGS. 8A to 9D , and a description thereof will be omitted. 
         [0095]    In light flux controlling member  500  according to Embodiment 3, the thickness of flange  560  in the central axis CA direction is small. As described above, the thickness of flange  560  is not limited, and can be determined in view of the required area of emission surface  330 , formability of flange  560 , and the like. In light flux controlling members  300  and  400  according to Embodiments 1 and 2, part of light entered light flux controlling members  300  and  400  from the vicinity of the openings of recesses  310  directly reaches flange  360 . Since flange  360  is not intended for controlling the distribution of light, it is not desirable that light directly reach flange  360 . In light flux controlling member  500  according to the present embodiment, more light entered from the vicinity of the opening of recess  310  can directly reach emission surface  330 . In the present embodiment, flange  560  is formed lower (rear surface  340  side) than a line (dashed line in  FIG. 20 ) passing through opening edge P 1  of recess  310  and the innermost point P 2  of reflection portion  350  (ring formed groove) in a cross-section including central axis CA. In this way, emission surface  330  of light flux controlling member  500  according to Embodiment 3 is formed larger than emission surface  330  of light flux controlling member  300  according to Embodiment 1, and can output more controlled light. 
         [0000]    (Simulation of Illuminance Distribution in Region under Light Flux Controlling Member) 
         [0096]    For light flux controlling member  500  according to Embodiment 3 illustrated in  FIG. 20  (hereinafter also referred to as light flux controlling member (f)), the illuminance distribution in a region under the light flux controlling member was simulated. For comparison, the illuminance distribution in a region under the light flux controlling member was also simulated for: conventional light flux controlling member  20  (hereinafter also referred to as light flux controlling member (a)) illustrated in  FIGS. 1A to 1C ; light flux controlling member  30  (hereinafter also referred to as light flux controlling member (b)) disclosed in PTL 1 illustrated in  FIGS. 3A to 3C ; light flux controlling member  300  (hereinafter also referred to as light flux controlling member (c)) according to Embodiment 1 illustrated in  FIGS. 8A to 9D ; light flux controlling member (d) whose flange is made thinner in conventional light flux controlling member  20  (light flux controlling member (a)) so that light entered from the vicinity of the opening of the recess can directly reach the emission surface; and light flux controlling member (e) whose flange is made thinner in light flux controlling member  30  (light flux controlling member (b)) disclosed in PTL 1 so that light entered from the vicinity of the opening of the recess can directly reach the emission surface. The amounts of light fluxes in the regions under light flux controlling members (b) to (f) were calculated relative to the amount of light flux in the region under conventional light flux controlling member  20  (light flux controlling member (a)) as 100%. 
         [0097]    In the simulation, the amount of light flux to the surface of substrate  210  when light emitting element  220  and each of light flux controlling members (a) to (f) are disposed on substrate  210  illustrated in  FIG. 7  was measured. Parameters for each of light flux controlling members (a) to (f) are the same as in the simulation carried out in Embodiment 1 except for the thickness of the flange. The thicknesses of the flanges of light flux controlling members (a), (b) and (c) in the central axis CA direction are 2.35 mm, and the thicknesses of the flanges of light flux controlling members (d), (e) and (f) in the central axis CA direction are 1.7 mm. The light flux controlling members used in the simulation, the thicknesses of flanges, the relative values of the amounts of light fluxes to substrate  210  are shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Light flux controlling 
                   
                   
                   
                   
                   
                   
               
               
                 member 
                 a 
                 b 
                 c 
                 d 
                 e 
                 f 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Feature of rear surface 
                 Flat surface 
                 Inclining surface 
                 Inclining surface 
                 Flat surface 
                 Inclining surface 
                 Inclining surface 
               
               
                   
                   
                   
                 linear protrusions 
                   
                   
                 linear protrusions 
               
               
                 Thickness of flange (mm) 
                 2.35 
                 2.35 
                 2.35 
                 1.7 
                 1.7 
                 1.7 
               
               
                 Relative value of amount 
                 100 
                 81 
                 71 
                 97 
                 78 
                 64 
               
               
                 of light flux (%) 
                   
                   
                   
                   
                   
                   
               
               
                   
               
             
          
         
       
     
         [0098]    As shown in Table 1, the amount of light flux is low in the region under the light flux controlling members (d) to (f) having thin flange (1.7 mm), in which even light entered from the vicinity of the opening of the recess can directly reach the emission surface, compare to light flux controlling members (a) to (c) having thick flange (2.35 mm), in which part of light entered from the vicinity of the opening of the recess directly reaches the flange. Further, the amount of light flux is low in the region under light flux controlling member (f) according to the present embodiment, which has an inclining surface, a plurality of linear protrusions and the thin flange, compare to light flux controlling members (a) and (d) having no inclining surface, light flux controlling members (b) and (e) having inclining surfaces (but not having a plurality of linear protrusions), and light flux controlling member (c) having an inclining surface, a plurality of linear protrusions and the thick flange. It can be understood that light flux controlling member (f) according to the present embodiment can control the distribution of more light. 
       (Effect) 
       [0099]    Light flux controlling member  500  according to Embodiment 3 has the same effect as light flux controlling member  300  according to Embodiment 1. Further in light flux controlling member  500  according to Embodiment 3, flexibility of design of emission surface  330  can be enhanced by forming thin flange  560 . Further, light flux controlling member  500  according to Embodiment 3 can control the distribution of more light due to large emission surface  330 . 
         [0100]    When trying to form emission surface  330  without flange  560 , which can control traveling directions of light to required light emitting directions, the diameter of the light flux controlling member may increase. In that case, the light flux controlling member may be appropriately designed with due considerations of the balance between the form of the light flux controlling member and emitted light. 
         [0101]    This application claims priority based on Japanese Patent Application No. 2012-186459, filed on Aug. 27, 2012, and Japanese Patent Application No. 2013-064009 filed on Mar. 26, 2013, the entire contents of which including the specifications and the drawings are incorporated herein by reference. 
       INDUSTRIAL APPLICABILITY 
       [0102]    The light flux controlling member, light emitting device and surface light source device of the present invention may be employed in a backlight of a liquid crystal display apparatus or a general lighting. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  light emitting element 
           20 ,  30  light flux controlling member 
           22  incidence surface 
           24  emission surface 
           26  rear surface 
           32  inclining surface 
           100  surface light source device 
           110  casing 
           112  bottom plate 
           114  top plate 
           120  light diffusion member 
           200  light emitting device 
           210  substrate 
           220  light emitting element 
           300 ,  400 ,  500  light flux controlling member 
           310  recess 
           320  incidence surface 
           330  emission surface 
           340  rear surface 
           342  light scattering surface 
           350 ,  450  reflection portion 
           352  linear protrusion 
           352   a  first reflection surface 
           352   b  second reflection surface 
           352   c  ridge line 
           360 ,  560  flange 
           370  leg 
           440   a  first rear surface 
           440   b  second rear surface 
         P 1  opening edge of recess 
         P 2  innermost point of reflection portion