Abstract:
This light flux control member comprises an entry surface, a reflective surface, a circular groove containing a first circular surface and a second circular surface, and an exit surface. The circular groove is disposed in such a manner as not to intersect with the optical path of a light from the entry surface to the reflective surface, and, in such a manner as to intersect with at least a portion of the optical path of a light, from being emitted from a point other than the center of the light-emitting element, entering at the entry surface and being reflected at the reflective surface, to reaching the exit surface. The second circular surface is formed in such a manner that the width of the circular groove widens as the opening ridges of the circular groove is approached from the valley portion of the circular groove.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a light flux controlling member that controls distribution of light emitted from a light emitting element. In addition, the present invention relates to a light-emitting device, a surface light source device and a display apparatus which include the light flux controlling member. 
       BACKGROUND ART 
       [0002]    Some transmission type image display apparatuses such as liquid crystal display apparatuses use a direct surface light source device as a backlight. In recent years, direct surface light source devices having a plurality of light emitting elements as the light source have been used. 
         [0003]    For example, a direct surface light source device includes a substrate, a plurality of light emitting elements, a plurality of light flux controlling members and a light diffusion member. The light emitting elements are disposed on the substrate in a matrix. A light flux controlling member configured to expand the light emitted from each light emitting element in the surface direction of the substrate is disposed above each light emitting element. The light emitted from the light flux controlling member is diffused by the light diffusion member so as to illuminate a member to be illuminated (for example, a liquid crystal panel) in a planar fashion (see, for example, PTL 1). 
         [0004]    The surface light source device disclosed in PTL 1 includes a housing, a substrate disposed in the housing, a light emitting element disposed on the substrate, a light flux controlling member disposed on the substrate to cover the light emitting element and to control the distribution of the light emitted from the light emitting element (light direction conversion optical device), and a light diffusion member (diffusion transmission section) configured to allow the light emitted from the light flux controlling member to pass therethrough while diffusing the light. The light flux controlling member includes an incidence surface on which the light emitted from the light emitting element is incident, a reflection surface formed on the side opposite to the incidence surface and configured to reflect the incident light in the lateral direction, and an emission surface configured to emit the light reflected by the reflection surface. 
         [0005]    The light emitted from the light emitting element is incident on the light flux controlling member from the incidence surface. The light incident on the light flux controlling member is laterally reflected by the reflection surface, and emitted to the outside of the light flux controlling member from the emission surface. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1 
         [0007]    Japanese Patent Application Laid-Open No. 2007-048883 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    However, in the surface light source device disclosed in PTL 1, a part of the light laterally emitted from the emission surface directly travels through the air and reaches the housing. In this manner, a part of the light emitted from the emission surface does not reach the light diffusion member while being attenuated, and thus does not used in some situation. As such, disadvantageously, the surface light source device disclosed in PTL 1 cannot sufficiently use the light emitted from the light emitting element. 
         [0009]    In view of this, an object of the present invention is to provide a light flux controlling member which can increase the use efficiency of the light emitted from a light emitting element. 
         [0010]    In addition, anther object of the present invention is to provide a light-emitting device, a surface light source device and a display apparatus which include the light flux controlling member. 
       Solution to Problem 
       [0011]    A light flux controlling member according to embodiments of the present invention is a member for controlling a distribution of light emitted from a light emitting element, and includes: an incidence surface on which light emitted from the light emitting element is incident, the incidence surface being disposed on a rear side to intersect with a central axis thereof; a reflection surface configured to reflect light incident on the incidence surface in a lateral direction, the reflection surface being disposed on a front side such that a distance from the light emitting element increases from a center portion toward an outer periphery portion thereof; an annular groove including a first annular surface and a second annular surface and disposed on a rear side at a position outside the incidence surface to surround the central axis, the first annular surface being disposed on the central axis side, the second annular surface being disposed outside the first annular surface; and an emission surface configured to emit light reflected by the reflection surface, the emission surface being disposed outside the annular groove to surround the central axis. The annular groove is disposed such that the annular groove does not intersect with a light path of light emitted from a center of the light emitting element in a region from a point of incidence of the light on the incidence surface to a point of reflection of the light at the reflection surface and that the annular groove intersects with at least a part of a light path of light which is emitted from the light emitting element and is incident on the incidence surface in a region from a point of reflection of the light at the reflection surface to a point of arrival of the light at the emission surface, and the second annular surface is formed such that a width of the annular groove increases toward an opening edge of the annular groove from a valley part of the annular groove, the second annular surface being configured to refract, toward the front side, light emitted from the light emitting element which is incident on the incidence surface and is reflected by the reflection surface. 
         [0012]    A light-emitting device according to embodiments of the present invention includes: a light emitting element, and the above-mentioned light flux controlling member. The light flux controlling member is disposed such that the central axis coincides with an optical axis of the light emitting element. 
         [0013]    A surface light source device according to embodiments of the present invention includes: the above-mentioned light-emitting device; and a light diffusion member configured to allow light from the light-emitting device to pass therethrough while diffusing the light. 
         [0014]    A display apparatus according to embodiments of the present invention includes: the above-mentioned surface light source device; and a display member to which light emitted from the surface light source device is applied. 
       Advantageous Effects of Invention 
       [0015]    A light-emitting device which has the light flux controlling member and the light flux controlling member according to embodiments of present invention can increase the use efficiency of light emitted from a light emitting element. Accordingly, the surface light source device and the display apparatus according to the embodiments of the present invention can reduce luminance unevenness in comparison with the conventional apparatuses. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIGS. 1A and 1B  illustrate an external appearance of a configuration of a surface light source device according to Embodiment 1; 
           [0017]      FIGS. 2A and 2B  are sectional views illustrating a configuration of the surface light source device according to Embodiment 1; 
           [0018]      FIG. 3  is a partially enlarged sectional views of  FIG. 2B ; 
           [0019]      FIGS. 4A to 4D  illustrate a configuration of the light flux controlling member according to Embodiment 1; 
           [0020]      FIG. 5  is a partially enlarged sectional view of  FIG. 4D ; 
           [0021]      FIGS. 6A and 6B  illustrate simulations of light paths in light flux controlling members according to Embodiment 1 and Comparative Example 1; 
           [0022]      FIGS. 7A to 7D  are sectional views of a light flux controlling member according to Embodiment 2; 
           [0023]      FIG. 8  is a sectional view of the light flux controlling member according to the comparative example; 
           [0024]      FIGS. 9A and 9B  illustrate simulations of light paths in light flux controlling members according to Embodiment  2  and Comparative Example 2; and 
           [0025]      FIGS. 10A to 10C  illustrate simulations of illuminance distributions using the light flux controlling members of Embodiment 2 and Comparative Example 2. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    In the following, embodiments of the present invention are described in detail with reference to the accompanying drawings. In the following description, as a typical example of the surface light source device according to the embodiments of the present invention, a surface light source device suitable for a backlight of a liquid crystal display apparatus will be described. With a member (for example, a liquid crystal panel) configured to be irradiated with light from the surface light source device, the surface light source device can be used as a display apparatus. 
       Embodiment 1 
       [0027]    (Configurations of Surface Light Source Device and Light-Emitting Device) 
         [0028]      FIGS. 1 to 3  illustrate a configuration of surface light source device  100  according to Embodiment 1.  FIG. 1A  is a plan view of surface light source device  100  according to Embodiment 1, and  FIG. 1B  is a front view of surface light source device  100 .  FIG. 2A  is a sectional view taken along line A-A of  FIG. 1B , and  FIG. 2B  is a sectional view taken along line B-B of  FIG. 1A .  FIG. 3  is a partially enlarged sectional view of  FIG. 2B . 
         [0029]    As illustrated in  FIG. 1A  to  FIG. 2B , surface light source device  100  according to Embodiment 1 includes housing  120 , light diffusion member  140  and a plurality of light-emitting devices  160 . Light-emitting devices  160  are disposed on bottom plate  122  of housing  120  in a matrix. The internal surface of bottom plate  122  functions as a diffusion reflection surface. In addition, a top plate of housing  120  is provided with an opening. Light diffusion member  140  is disposed in such a manner as to close the opening, and functions as a light emitting surface. The size of the light emitting surface is not limited, and is, for example, approximately 400 mm×approximately 700 mm (32 inch). 
         [0030]    As illustrated in  FIG. 3 , light-emitting devices  160  are fixed on respective substrates  124 . A plurality of substrates  124  are fixed at respective positions on bottom plate  122  of housing  120 . Each of light-emitting devices  160  includes light emitting element  162  and light flux controlling member  200 . 
         [0031]    Light emitting element  162  is a light source of surface light source device  100 , and is mounted on substrate  124 . Light emitting element  162  is, for example, a light-emitting diode (LED) such as a white light-emitting diode. 
         [0032]    Light flux controlling member  200  is a diffusion lens configured to control the distribution of light emitted from light emitting element  162 , and is fixed on substrate  124 . Light flux controlling member  200  is disposed over light emitting element  162  in such a manner that its central axis CA coincides with optical axis LA of light emitting element  162 . It is to be noted that each of reflection surface  220  and emission surface  240  of light flux controlling member  200  described later is rotationally symmetric (circularly symmetric), and the rotational axes thereof coincide with each other. The rotational axes of reflection surface  220  and emission surface  240  are referred to as “central axis CA of the light flux controlling member.” In addition, “optical axis LA of the light emitting element” means the central light beam of a stereoscopic light flux emitted from light emitting element  162 . A gap for dissipating the heat emitted from light emitting element  162  to the outside is formed between substrate  124  on which light emitting element  162  is mounted and incidence surface  210  of light flux controlling member  200 . 
         [0033]    Light flux controlling member  200  is formed by integral molding. The material of light flux controlling member  200  is not particularly limited as long as the light having a desired wavelength can pass through the material. Examples of the material of light flux controlling member  200  include: light transmissive resins such as polymethylmethacrylate (PMMA), polycarbonate (PC), and epoxy resin (EP); or glass. 
         [0034]    Surface light source device  100  according to the present embodiment is characterized mainly by the configuration of light flux controlling member  200 . In view of this, the details of light flux controlling member  200  are described later. 
         [0035]    Light diffusion member  140  is a plate-shaped member having a light diffusing property and allows the light emitted from light-emitting device  160  to pass therethrough while diffusing the light. Normally, the size of light diffusion member  140  is substantially the same as that of the member to be irradiated such as a liquid crystal panel. For example, light diffusion member  140  is formed of a light transmissive resin such as polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and styrene methyl methacrylate copolymerization resin (MS). In order to provide a light diffusing property, minute irregularities are formed on the surface of light diffusion member  140 , or diffusing members such as beads are dispersed in light diffusion member  140 . 
         [0036]    In surface light source device  100  according to the present embodiment, light emitted from light emitting elements  162  are expanded by respective light flux controlling members  200  so as to illuminate a wide range of light diffusion member  140 . The light emitted from each light flux controlling member  200  is further diffused by light diffusion member  140 . As a result, surface light source device  100  according to the present embodiment can uniformly illuminate a planar member (for example, a liquid crystal panel). 
         [0037]    (Configuration of Light Flux Controlling Member) 
         [0038]      FIG. 4A  to  FIG. 4D  and  FIG. 5  illustrate a configuration of light flux controlling member  200  according to Embodiment 1.  FIG. 4A  is a plan view of light flux controlling member  200  according to Embodiment 1,  FIG. 4B  is a bottom view of light flux controlling member  200 ,  FIG. 4C  is a side view of light flux controlling member  200 , and  FIG. 4D  is a sectional view taken along line A-A of  FIG. 4B .  FIG. 5  is a partially enlarged sectional view of  FIG. 4D . 
         [0039]    As illustrated in  FIG. 4A  to  FIG. 4D  and  FIG. 5 , light flux controlling member  200  includes incidence surface  210 , reflection surface  220 , annular groove  230  and emission surface  240 . 
         [0040]    Incidence surface  210  is a plane disposed at a center portion on the rear (light emitting element  162 ) side of light flux controlling member  200 . Incidence surface  210  is orthogonal to optical axis LA, and refracts the incident light toward reflection surface  220 . The shape in plan view of incidence surface  210  is not limited, and incidence surface  210  has a circular shape in plan view in the present embodiment. 
         [0041]    Light incident on incidence surface  210  is laterally reflected by reflection surface  220 . Light flux reflection surface  220  is a surface rotationally symmetrical (circularly symmetrical) about central axis CA of controlling member  200 . In addition, the generatrix of the rotationally symmetrical surface extending from the center to the outer periphery portion thereof is a recessed curve with respect to light emitting element  162 , and reflection surface  220  is a curved surface obtained by rotating the generatrix 360 degrees about central axis CA (see  FIG. 4 ). That is, reflection surface  220  has a curved surface having an aspherical shape whose height from light emitting element  162  increases from the center portion toward the outer periphery portion. In addition, the external peripheral portion of reflecting surface  220  is formed at a position distant from light-emitting element  162  in the direction of optical axis LA of light-emitting elements  162  (in height) relative to the center of reflecting surface  220 . For example, reflecting surface  220  is a curved surface of an aspherical shape whose height from light-emitting element  162  increases from the center toward the external peripheral portion, or a curved surface of an aspherical shape whose height from light-emitting element  162  (substrate  124 ) increases from the center portion toward a predetermined point and whose height from light-emitting element  162  decreases from the predetermined point toward the external peripheral portion. In the former case, the inclination angle of reflecting surface  220  relative to the surface direction of substrate  124  decreases from the center toward the external peripheral portion. In the latter case, on the other hand, reflecting surface  220  has a point where the inclination angle relative to the surface direction of substrate  124  is zero (in parallel with substrate  124 ) at a position nearer to the external peripheral portion between the center and the external peripheral portion. It is to be noted that, while the term “generatrix” generally means a straight line that defines a ruled surface, the term “generatrix” used in the present invention includes curves for defining total reflection surface  220  which is a rotationally symmetrical surface. 
         [0042]    Annular groove  230  is disposed on the rear side to surround central axis CA at a position on the outside relative to incidence surface  210 . Annular groove  230  refracts a part of the light reflected by reflection surface  220  toward the front side. Annular groove  230  includes first annular surface  232  and second annular surface  234 . The cross-sectional shape including central axis CA of annular groove  230  is not limited as long as first annular surface  232  and second annular surface  234  are provided and the above-described function can be achieved. In the present embodiment, the cross-sectional shape of annular groove  230  including central axis CA is a triangular shape. Specifically, in the present embodiment, ridgeline  236  is formed at a valley part between first annular surface  232  and second annular surface  234 . Annular groove  230  is formed such that the width of the groove increases from the valley part toward the opening edge. In addition, the depth of annular groove  230  in the cross-section including central axis CA may be constant or varied in the circumferential direction around central axis CA as the rotational axis. In the present embodiment, the depth of annular groove  230  in the cross-section including central axis CA is constant in the circumferential direction around central axis CA as the rotational axis. In addition, the width of annular groove  230  in the cross-section including central axis CA may be constant or varied in the circumferential direction around central axis CA as the rotational axis. In the present embodiment, the width of annular groove  230  in the cross-section including central axis CA is constant in the circumferential direction around central axis CA as the rotational axis. That is, in the present embodiment, annular groove  230  is rotationally symmetrical about central axis CA. Preferably, the valley part of annular groove  230  is disposed on the front side relative to the center portion of reflection surface  220  (see the up-down arrow in  FIG. 5 ). Here, the valley part of annular groove  230  means “the deepest position from the opening in annular groove  230 .” 
         [0043]    First annular surface  232  is disposed on central axis CA side to surround central axis CA. The inclination direction of first annular surface  232  to central axis CA is not limited. First annular surface  232  may be disposed such that it approaches the front side of light flux controlling member  200  as the distance from central axis CA increases. That is, first annular surface  232  may have a shape of the side surface of an inverted truncated-cone shape. With this configuration, at the time of the injection molding of light flux controlling member  200 , light flux controlling member  200  is easily removed from the metal mold. In addition, first annular surface  232  may be disposed parallel to central axis CA. That is, first annular surface  232  may have a shape of the side surface of a column 
         [0044]    Second annular surface  234  is disposed on the outside relative to first annular surface  232  to surround central axis CA. In addition, second annular surface  234  is disposed such that it approaches the rear side from central axis CA side (center portion) toward the outer periphery portion. The cross-sectional shape including central axis CA of second annular surface  234  is not limited. The cross-sectional shape including central axis CA of second annular surface  234  includes a straight line or a curved line. Examples of the curved line include an arc whose curvature center is located on the outside, an arc whose curvature center is located on the inside, and the like. In the present embodiment, the cross-sectional shape including central axis CA of second annular surface  234  is a straight line. That is, second annular surface  234  has a shape of the side surface of a truncated cone. 
         [0045]    Ridgeline  236  is a boundary line between first annular surface  232  and second annular surface  234 , and is disposed to surround central axis CA. Preferably, ridgeline  236  (the valley part of annular groove  230 ) is disposed on the front side relative to the center portion of reflection surface  220  (see the up-down arrow in  FIG. 5 ). 
         [0046]    Emission surface  240  emits the light reflected by reflection surface  220  to the outside of light flux controlling member  200 . Emission surface  240  is disposed to surround central axis CA. In the present embodiment, emission surface  240  is a curved surface extending along central axis CA. In the cross-section including central axis CA, the upper end of emission surface  240  is connected with reflection surface  220 . On the other hand, in the cross-section including central axis CA, the lower end of emission surface  240  is connected with second annular surface  234 . 
         [0047]    Leg part  180  is a part for setting the position of the light flux controlling member main body including incidence surface  210 , reflection surface  220 , annular groove  230  and emission surface  240  with respect to substrate  124 . In the present embodiment, three leg parts  180  are disposed on incidence surface  210 . 
         [0048]    (Simulation) 
         [0049]    With light flux controlling member  200  of Embodiment 1, the light path of the light emitted from light emitting element  162  was simulated. In addition, a similar simulation was conducted with light flux controlling member  200 ′ provided with no annular groove  230  (hereinafter also referred to as “light flux controlling member  200 ′ according to the comparative example”) for comparison. 
         [0050]      FIG. 6A  illustrates light paths of the light emitted from the center of the light emitting surface of light emitting element  162  in light flux controlling member  200 ′ according to Comparative Example 1, and  FIG. 6B  illustrates light paths of the light emitted from the center of the light emitting surface of light emitting element  162  in light flux controlling member  200  according to Embodiment 1. It is to be noted that leg part  180  is omitted in  FIG. 6A  and  FIG. 6B . 
         [0051]    As illustrated in  FIG. 6A , in light flux controlling member  200 ′ according to Comparative Example 1, a part of light emitted from the center of light emitting element  162  is incident on incidence surface  210 , and is refracted toward reflection surface  220 . The light having entered light flux controlling member  200 ′ is laterally reflected by reflection surface  220 . Then, the light reflected by reflection surface  220  is emitted to the outside of light flux controlling member  200 ′ from emission surface  240 . At this time, the light emitted from light flux controlling member  200 ′ advances in the lateral direction. 
         [0052]    On the other hand, as illustrated in  FIG. 6B , in light flux controlling member  200  according to Embodiment 1, a part of the light emitted from the center of light emitting element  162  is incident on incidence surface  210 , and is refracted toward reflection surface  220 . The light having entered light flux controlling member  200  is laterally reflected by reflection surface  220 . Then, a part of the light reflected by reflection surface  220  (the light reflected by reflection surface  220  at a portion on emission surface  240  side) is emitted from emission surface  240  to the outside of light flux controlling member  200 . In addition, a part of the light reflected by reflection surface  220  (the light reflected by reflection surface  220  at a portion on central axis CA side) is emitted from first annular surface  232  to the outside of light flux controlling member  200 . At this time, since first annular surface  232  is substantially parallel to central axis CA, the light emitted at first annular surface  232  is not largely refracted. In addition, the light emitted from first annular surface  232  enters light flux controlling member  200  from second annular surface  234 . At this time, the light incident on second annular surface  234  is largely refracted toward the front side since second annular surface  234  is disposed to approach the rear side from the center portion toward the outer periphery portion. In this manner, a part of the light reflected on the rear side of reflection surface  220  is refracted toward the front side by first annular surface  232  and second annular surface  234 . Then, the light refracted toward the front side is emitted from emission surface  240  to the outside of light flux controlling member  200 . 
         [0053]    (Effect) 
         [0054]    As described above, in light flux controlling member  200  according to Embodiment 1, annular groove  230  for refracting light to the front side is formed on a part of the light path of the light reflected by reflection surface  220 , and therefore a part of the light reflected by reflection surface  220  is emitted toward the front side. Thus, light flux controlling member  200  according to Embodiment 1 can efficiently use the light emitted from light emitting element  162 . In addition, in surface light source device  100  according to Embodiment 1, the waveform of the illuminance distribution can be improved. 
       Embodiment 2 
       [0055]    The surface light source device according to Embodiment 2 is different from surface light source device  100  according to Embodiment 1 only in the configuration of light flux controlling member  300 . In view of this, only light flux controlling member  300  according to Embodiment 2 is described below. 
         [0056]    (Configuration of Light Flux Controlling Member) 
         [0057]      FIGS. 7A to 7D  illustrate a configuration of light flux controlling member  300  according to Embodiment 2.  FIG. 7A  is a plan view of light flux controlling member  300  according to Embodiment 2,  FIG. 7B  is a bottom view of light flux controlling member  300 , 
         [0058]      FIG. 7C  is a front view of light flux controlling member  300 , and  FIG. 7D  is a sectional view taken along line A-A of  FIG. 7B . 
         [0059]    As illustrate in  FIGS. 7A to 7D , light flux controlling member  300  according to Embodiment 2 of the present invention includes incidence surface  310 , reflection surface  220 , annular groove  230 , emission surface  240  and inspection reference surface  350 . 
         [0060]    Incidence surface  310  includes an inner incidence surface including recessed surface  312  and rear surface  314 , and an outer inclined surface including inclined surface  316 . 
         [0061]    Recessed surface  312  is formed at a center portion of the rear side (light emitting element  162  side) of light flux controlling member  300 . Recessed surface  312  allows for incidence of a part of the light emitted from light emitting element  162 . In the present embodiment, recessed surface  312  is a rotationally symmetrical (circularly symmetrical) surface having a substantially spherical cap shape which is formed so as to approach light emitting element  162  as the distance from optical axis LA increases. The central axis of recessed surface  312  and central axis CA of light flux controlling member  300  coincide with each other. In in the light emitted from light emitting element  162 , light having a small angle to optical axis LA is incident on recessed surface  312 . 
         [0062]    Rear surface  314  is disposed outside recessed surface  312 . Rear surface  314  allows for incidence of a part of the light emitted from light emitting element  162 . In the present embodiment, rear surface  314  is a plane perpendicular to central axis CA. Rear surface  314  extends from the outer peripheral edge of recessed surface  312  in the direction orthogonal to central axis CA. In the light emitted from light emitting element  162 , light having a larger angle to optical axis LA than that of the light incident on recessed surface  312  is incident on rear surface  314 . 
         [0063]    Inclined surface  316  is disposed outside rear surface  314 . Inclined surface  316  allows for incidence of a part of the light emitted from light emitting element  162 . Inclined surface  316  is disposed such that the distance from light emitting element  162  increases as the distance from central axis CA (optical axis LA) increases. Inclined surface  316  is formed at an angle at which inclined surface  316  does not intersect with the light path of the light which is emitted from the center of the light emitting surface of light emitting element  162  and is incident on the outer edge of the inner incidence surface. That is, in the light emitted from the center of the light emitting surface of light emitting element  162 , light having a larger angle to optical axis LA than that of the light incident on rear surface  314  is not incident on the inclined surface, and a part of the light emitted from an end portion of light emitting element  162  is incident on inclined surface  316 . 
         [0064]    Inspection reference surface  350  is disposed on the front side relative to inclined surface  316 , and on the outside of inclined surface  316 . The light emitted from the center of the light emitting surface of light emitting element  162  does not directly reach inspection reference surface  350 . Inspection reference surface  350  is a plane perpendicular to central axis CA. Inspection reference surface  350  extends from the outer peripheral edge of inclined surface  316  in the direction orthogonal to central axis CA. Leg part  180  is fixed on inspection reference surface  350 . With this configuration, the size in the height direction of leg part  180 , emission surface  240  described later and the like of light flux controlling member  300  can be easily inspected based on inspection reference surface  350 . In the present embodiment, leg part  180  is provided on inspection reference surface  350 . 
         [0065]    Annular groove  230  is disposed outside inspection reference surface  350  on the rear side. 
         [0066]    (Simulation) 
         [0067]    In light flux controlling member  300  according to Embodiment 2, the light path of light emitted from light emitting element  162 , and brightness on the diffusion plate when the diffusion plate is installed on light flux controlling member  300  were simulated. In addition, a similar simulation was conducted with light flux controlling member  300 ′ provided with no annular groove  230  (hereinafter also referred to as “light flux controlling member according to the comparative example 2”; see  FIG. 8 ) for comparison. While the effect of the light emitted from the center of light emitting element  162  was confirmed in the simulation in Embodiment 1, the effect of the light emitted from an end portion of light emitting element  162  was also confirmed in Embodiment 2. 
         [0068]      FIG. 9A  illustrates light paths of light emitted from the light emitting surface of light emitting element  162  in light flux controlling member  300 ′ according to the comparative example 2, and  FIG. 9B  illustrates light paths of light emitted from the light emitting surface of light emitting element  162  in light flux controlling member  300  according to Embodiment 2. It is to be noted that hatching and leg part  180  are omitted in  FIG. 9A  and  FIG. 9B . 
         [0069]    As illustrated in  FIG. 9A , in light flux controlling member  300 ′ according to the comparative example, a part of the light emitted from light emitting element  162  is incident on incidence surface  310  and is refracted toward reflection surface  220 . The light having entered light flux controlling member  300 ′ is laterally reflected by reflection surface  220 . Then, the light reflected by reflection surface  220  is emitted to the outside of light flux controlling member  300 ′ from emission surface  240 . 
         [0070]    On the other hand, as illustrated in  FIG. 9B , in light flux controlling member  300  according to Embodiment  2 , a part of the light emitted from light emitting element  162  is incident on incidence surface  310 , and refracted toward reflection surface  220 . The light having entered light flux controlling member  300  is laterally reflected by reflection surface  220 . Then, a part of the light reflected by reflection surface  220  (the light reflected by reflection surface  220  at a portion on emission surface  240  side) is emitted to the outside of light flux controlling member  300  from emission surface  240 . In addition, a part of the light reflected by reflection surface  220  (the light reflected by reflection surface  220  at a portion on central axis CA side) is emitted to the outside of light flux controlling member  300  from first annular surface  232 . At this time, since first annular surface  232  is substantially parallel to central axis CA, the light emitted at first annular surface  232  is not largely refracted. In addition, the light emitted from first annular surface  232  enters light flux controlling member  300  from second annular surface  234 . At this time, since second annular surface  234  is disposed to approach the rear side from the center portion toward the outer periphery portion, the light incident on second annular surface  234  is largely refracted toward the front side. As described, a part of the light reflected on the rear side of reflection surface  220  is refracted toward the front side by first annular surface  232  and second annular surface  234 . Then, the light refracted toward the front side is emitted to the outside of light flux controlling member  300  from emission surface  240 . 
         [0071]      FIG. 10A  shows an illuminance distribution on the diffusion plate in the case where light flux controlling member  300  according to Embodiment 2 is used,  FIG. 10B  shows an illuminance distribution on the diffusion plate in the case where light flux controlling member  300 ′ according to the comparative example 2 is used, and  FIG. 10C  shows an illuminance distribution on the diffusion plate in a cross-section including optical axis LA. The ordinate and abscissa of  FIG. 10A , the ordinate and abscissa of  FIG. 10B , and the abscissa of  FIG. 10C  represent the distance (mm) from the intersection of optical axis LA and the diffusion plate. In addition, the ordinate of  FIG. 10C  represents the illuminance (lux). In addition, in  FIG. 10C , the solid line represents an illuminance in the case where light flux controlling member  300  according to Embodiment 2, and the broken line represents an illuminance in the case where light flux controlling member  300 ′ according to the comparative example 2 is used. 
         [0072]    As illustrated in  FIGS. 10A to 10C , when light flux controlling member  300  according to Embodiment 1 is used, the quantity of the light controlled toward the upper side is large in comparison with the case where light flux controlling member  300 ′ according to the comparative example 2 is used (see, in particular, the dashed line in  FIG. 10C ). As described above, the reason for this is that a part of the light travelling in the lateral direction is refracted toward the front side mainly by first annular surface  232  and second annular surface  234 . 
         [0073]    (Effect) 
         [0074]    As described above, light flux controlling member  300  according to Embodiment 2 has an effect similar to that of light flux controlling member  200  according to Embodiment 1. In addition, the weight of light flux controlling member  300  according to Embodiment 2 can be reduced in comparison with light flux controlling member  200  of Embodiment 1. 
         [0075]    This application is entitled to and claims the benefit of Japanese Patent Application No. 2014-076152 filed on Apr. 2, 2014, the disclosure each of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0076]    The light flux controlling member, the light-emitting device and the surface light source device according to the embodiments of the present invention are applicable to, for example, a backlight of liquid crystal display apparatuses or generally-used illumination apparatuses. 
       REFERENCE SIGNS LIST 
       [0077]      100  Surface light source device 
         [0078]      120  Housing 
         [0079]      122  Bottom plate 
         [0080]      124  Substrate 
         [0081]      140  Light diffusion member 
         [0082]      160  Light-emitting device 
         [0083]      162  Light emitting element 
         [0084]      180  Leg part 
         [0085]      200 ,  200 ′,  300 ,  300 ′ Light flux controlling member 
         [0086]      210 ,  310  Incidence surface 
         [0087]      220  Reflection surface 
         [0088]      230  Annular groove 
         [0089]      232  First annular surface 
         [0090]      234  Second annular surface 
         [0091]      236  Ridgeline 
         [0092]      240  Emission surface 
         [0093]      312  Recessed surface 
         [0094]      314  Rear surface 
         [0095]      316  Inclined surface 
         [0096]      350  Inspection reference surface 
         [0097]    CA Central axis 
         [0098]    LA Optical axis