Abstract:
This light-emitting device has a light-emitting element, whereof the shape in planar view is rectangular, for emitting light, and a light flux control member. The light flux control member has an entry surface, a back surface, and where grid-shaped protruding stripes comprising a plurality of protruding stripes disposed into a grid shape or grid-shaped recessed stripes comprising a plurality of recessed stripes disposed into a grid shape are formed; and an exit surface disposed on the surface facing away from the back surface, and where the light that has entered the entry surface is caused to exit. Of the angles formed by each of the four sides constituting the outer edges of the light-emitting element and a first virtual straight line that is parallel to the crest lines of the grid-shaped protruding stripes or the valley lines of the grid-shaped recessed stripes, the smaller angle is an acute angle.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a light emitting device and a light flux controlling member that is provided in the light emitting device. 
       BACKGROUND ART 
       [0002]    In recent years, light emitting diodes (hereinafter also referred to as “LEDs”) are used as a light source for illumination from a view point of energy saving and downsizing. Light emitting devices using a combination of an LED and a light flux controlling member that controls the distribution of light emitted from the LED are used in place of fluorescent lamps and halogen lamps. In addition, direct surface light source devices incorporating the light emitting device are used as a backlight in image display devices of transmission type such as liquid crystal display apparatuses (for example, PTL 1). 
         [0003]    The surface light source device disclosed in PTL 1 includes a substrate, a light emitting element (light emitting chip) disposed on the substrate, a light flux controlling member (lens) disposed on the substrate to cover the light emitting element and to control the distribution of the light emitted from the light emitting element, and a light diffusion member 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 light emitted from the light emitting element is incident, an emission surface configured to emit, to the outside, the light incident on the incidence surface, and a rear surface formed on the side opposite to the emission surface. 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 reaches the emission surface and is emitted from the emission surface to the outside. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1 
         Japanese Patent Application Laid-Open No. 2006-114863 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    Disadvantageously, in the surface light source device disclosed in PTL 1, a bright spot (bright band) having a ring-band shape is generated on the light diffusion member due to light incident on the rear surface of the light flux controlling member. 
         [0007]    It is conceivable to form a lattice-like protrusion or a lattice-like recess on the rear surface of the light flux controlling member for the purpose of reducing generation of the above-mentioned bright spot having a ring-band shape. In the case of a surface light source device including such a light flux controlling member, it is recognized that generation of the bright spot having a ring-band shape can be suppressed by diffusing light reaching the rear surface of the light flux controlling member by the lattice-like protrusion or the lattice-like recess. 
         [0008]    In addition, in recent years, with reduction in thickness of surface light source devices, a light emitting element and a light flux controlling member are disposed at positions close to each other in some situation. When the light emitting element and the light flux controlling member are disposed at a positions close to each other in a surface light source device including the above-described light flux controlling member in which a lattice-like protrusion or a lattice-like recess is formed on the rear surface, a part of light incident on the incidence surface reaches the slope surface composed of the lattice-like protrusion or the lattice-like recess inside the light flux controlling member. Then, the part of light reaching the slope surface formed by the lattice-like protrusion or the lattice-like recess inside the light flux controlling member internally reflected and emitted from the emission surface. As a result, when a light emitting element and a surface light source device are disposed at positions close to each other in the surface light source device including the light flux controlling member in which the lattice-like protrusion or the lattice-like recess is formed, illuminance unevenness can be disadvantageously caused due to light internally reflected by the lattice-like protrusion or the lattice-like recess of the light diffusion member of the light flux controlling member. 
         [0009]    In view of this, an object of the present invention is to provide a light emitting device and a light flux controlling member which can suppress unevenness in illuminance even in the case where a light emitting element and a light flux controlling member are disposed at positions close to each other. 
       Solution to Problem 
       [0010]    A light emitting device of an embodiment of present invention includes: a light emitting element having a rectangular shape in plan view, and configured to emit light; and a light flux controlling member including an incidence surface which is an internal surface of a recess disposed to intersect a light axis of the light emitting element, the incidence surface being configured to allow incidence of light emitted from the light emitting element, a rear surface extending from an edge of an opening of the recess in a radial direction to surround the light axis, the rear surface being a surface on which a lattice-like protrusion line composed of a plurality of protrusion lines disposed in a lattice shape or a lattice-like recess line composed of a plurality of recess lines disposed in a lattice shape is formed, and an emission surface disposed on a side opposite to the rear surface and configured to emit light incident on the incidence surface. In plan view, a smaller angle between each of four sides of an outer edge of the light emitting element and a first virtual line parallel to a ridgeline of the lattice-like protrusion line or a valley line of the lattice-like recess line is an acute angle. 
         [0011]    In addition, a light flux controlling member of an embodiment of the present invention is configured to control a distribution of light emitted from a light emitting element, the light flux controlling member including: an incidence surface which is an internal surface of a recess formed on a rear side to intersect a central axis of the light flux controlling member; a rear surface extending from an edge of an opening of the recess in a radial direction to surround the central axis; and an emission surface disposed on a side opposite to the rear surface side to intersect the central axis. A lattice-like protrusion line or a lattice-like recess line is disposed on the rear surface, the lattice-like protrusion line including a plurality of annular protrusions disposed to surround the central axis and a plurality of radial protrusion lines radially disposed around the central axis, the lattice-like recess line including a plurality of annular recesses disposed to surround the central axis and a plurality of radial recess lines radially disposed around the central axis. 
       Advantageous Effects of Invention 
       [0012]    The light emitting device of the embodiments of the present invention can suppress unevenness in illuminance even in the case where a light emitting element and a light flux controlling member are disposed at positions close to each other, in comparison with conventional light emitting devices. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a sectional view of a light emitting device according to Embodiment 1; 
           [0014]      FIG. 2A  to  FIG. 2E  illustrate a configuration of a light flux controlling member according to Embodiment 1; 
           [0015]      FIG. 3A  and  FIG. 3B  are bottom views of the light flux controlling member according to Embodiment 1; 
           [0016]      FIG. 4  is a drawing for describing a positional relationship between each of the four sides of the outer edge of a light emitting element and a lattice-like protrusion line; 
           [0017]      FIG. 5A  and  FIG. 5B  illustrate a configuration of a light flux controlling member according to a modification of Embodiment 1; 
           [0018]      FIG. 6A  and  FIG. 6B  illustrate a part of a bottom view of a light flux controlling member according to another modification of Embodiment 1; 
           [0019]      FIG. 7  is a sectional view of a light flux controlling member according to Embodiment 2; 
           [0020]      FIG. 8A  and  FIG. 8B  are bottom views of the light flux controlling member according to Embodiment 2; 
           [0021]      FIG. 9  is a drawing for describing a positional relationship between each of the four sides of the outer edge of a light emitting element and a lattice-like protrusion line; 
           [0022]      FIG. 10A  and  FIG. 10B  illustrate a configuration of a light flux controlling member according to a modification of Embodiment 2; 
           [0023]      FIG. 11A  and  FIG. 11B  illustrate a part of a bottom view of a light flux controlling member according to another modification of Embodiment 2; 
           [0024]      FIG. 12  is a sectional view of a light flux controlling member according to Embodiment 3; 
           [0025]      FIG. 13A  and  FIG. 13B  are bottom views of the light flux controlling member according to Embodiment 3; 
           [0026]      FIG. 14  is a drawing for describing a positional relationship between each of the four sides of the outer edge of a light emitting element and a lattice-like protrusion line; 
           [0027]      FIG. 15A  and  FIG. 15B  illustrate a configuration of a light flux controlling member according to a modification of Embodiment 3; 
           [0028]      FIG. 16A  and  FIG. 16B  illustrate a part of a bottom view of a light flux controlling member according to another modification of Embodiment 3; 
           [0029]      FIG. 17A  to  FIG. 17D  are bottom views of a light flux controlling member according to Comparative examples, and graphs illustrating measurement results of the illuminance distribution; 
           [0030]      FIG. 18A  to  FIG. 18D  are bottom views of the light flux controlling members according to the Embodiments, and graphs illustrating measurement results of the illuminance distribution; and 
           [0031]      FIG. 19A  and  FIG. 19B  are bottom views of the light flux controlling member according to the Embodiments, and graphs illustrating measurement results of the illuminance distribution. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
     (Configuration of Light Emitting Device) 
       [0033]      FIG. 1  is a sectional view of light emitting device  100  according to Embodiment 1. 
         [0034]    As illustrated in  FIG. 1 , light emitting device  100  includes light emitting element package  110 , and light flux controlling member  120  configured to control the distribution of light emitted from light emitting element package  110 . It is to be noted that, in  FIG. 1 , hatching of the cross section in light flux controlling member  120  is omitted. 
         [0035]    Light emitting element package  110  is, for example, a light emitting diode (LED) such as a white light emitting diode. Light emitting element package  110  is disposed on substrate  150 , for example. Light emitting element package  110  includes package substrate  111  and light emitting element (die)  112 . At the top surface of package substrate  111 , cavity  113  is formed. Internal surface  114  of cavity  113  functions as a reflecting surface. The material of package substrate  111  is ceramic, resin or the like. Light emitting element  112  is disposed at the bottom surface of cavity  113 . With light emitting element  112  disposed at the bottom surface of cavity  113 , sealing resin such as epoxy resin and silicone resin is encapsulated in cavity  113 . In the present embodiment, light emitting element package  110  has a rectangular shape in plan view. 
         [0036]      FIG. 2A  to  FIG. 3B  illustrate a configuration of light flux controlling member  120 .  FIG. 2A  is a plan view of light flux controlling member  120 ,  FIG. 2B  is a front view of light flux controlling member  120 ,  FIG. 2C  is a rear view of light flux controlling member  120 ,  FIG. 2D  is a left side view of light flux controlling member  120 , and  FIG. 2E  is a right side view of light flux controlling member  120 . In addition,  FIG. 3A  is a bottom view of light flux controlling member  120 , and  FIG. 3B  is an enlarged view of the region surrounded by the broken line in  FIG. 3A . 
         [0037]    As illustrated in  FIG. 2A  to  FIG. 3B , light flux controlling member  120  includes incidence surface  121  as the internal surface of recess  127 , rear surface  122 , and emission surface  123 . In addition, light flux controlling member  120  may include flange part  124  disposed outside emission surface  123 , leg part  125  for fixing light flux controlling member  120  to substrate  150  in such a manner as to set the position of light flux controlling member  120 , and protrusion  126  configured to indicate the position of leg part  125 . Light flux controlling member  120  is mounted on substrate  150  by fixing leg part  125  to substrate  150  in such a manner as to set the position of leg part  125  with protrusion  126  as a mark. At this time, in the relationship with light emitting element package  110 , light flux controlling member  120  is mounted on substrate  150  such that light axis LA of light emitting element  112  coincides with central axis CA of light flux controlling member  120  (see  FIG. 1 ). While the number of light emitting element package  110  is one in the present embodiment, a plurality of light emitting element packages  110  may be disposed for each light flux controlling member  120 . In the case where a plurality of light emitting element packages  110  are disposed, light axis LA is the light travelling direction at the center of the stereoscopic light flux from a plurality of light emitting element packages  110 . 
         [0038]    Light flux controlling member  120  is formed by integral molding. The material of light flux controlling member  120  is not limited as long as light of a desired wavelength can pass therethrough. Examples of the material of light flux controlling member  120  include light-transmissive resins such as polymethylmethacrylate (PMMA), polycarbonate (PC), and epoxy resin (EP), and glass. 
         [0039]    Recess  127  is formed at a center portion on the rear side (light emitting element package  110  side) of light flux controlling member  120  in such a manner as to intersect light axis LA of light emitting element  112  (central axis CA of light flux controlling member  120 ). The internal surface of recess  127  functions as incidence surface  121 . Incidence surface  121  allows most or all of light emitted from light emitting element package  110  to enter flux controlling member  120  while controlling the travelling direction of the light. Incidence surface  121  intersects central axis CA of light flux controlling member  120 , and is substantially rotationally symmetrical about (circularly symmetrical) central axis CA. 
         [0040]    Rear surface  122  is a plane which is located on the rear side of light flux controlling member  120  and extends in the radial direction from the edge of the opening of recess  127 . Rear surface  122  causes diffuse reflection of a part of light emitted from light emitting element package  110 , which is incident on incidence surface  121  and reflected by emission surface  123 . In addition, rear surface  122  causes diffuse reflection of light emitted from light emitting element package  110  at a large angle with respect to light axis LA. Rear surface  122  is a feature of the present invention, and the configuration of rear surface  122  is specifically described later. 
         [0041]    Emission surface  123  is formed on the front side of light flux controlling member  120  in such a manner as to protrude from flange part  124 . Emission surface  123  emits the light having entered light flux controlling member  120  to the outside while controlling the travelling direction of the light. Emission surface  123  intersects central axis CA, and rotationally symmetrical (circularly symmetrical) about central axis CA. 
         [0042]    Emission surface  123  includes first emission surface  123   a  located in a predetermined range around central axis CA, second emission surface  123   b  continuously formed at the periphery of first emission surface  123   a,  and third emission surface  123   c  configured to connect second emission surface  123   b  and flange part  124  (see  FIG. 1 ). First emission surface  123   a  is a smooth curved surface protruding in the light axis direction. First emission surface  123   a  has a recessed shape which is obtained by cutting out a part of a sphere. Second emission surface  123   b  is a smooth curved surface located at a periphery of first emission surface  123   a  and protruding in the light axis direction. Second emission surface  123   b  has a circular protruding shape. Third emission surface  123   c  is a curved surface located at a periphery of second emission surface  123   b.  In the cross section illustrated in  FIG. 1 , the cross section of third emission surface  123   c  may have a linear shape or a curved line shape. 
         [0043]    Next, with reference to  FIG. 3A  and  FIG. 3B , rear surface  122  is described in detail. On rear surface  122 , lattice-like protrusion line  130 , and annular groove  140  are formed. 
         [0044]    As illustrated in  FIG. 3A  and  FIG. 3B , lattice-like protrusion line  130  is disposed to surround recess  127 . The shape of the unit structure of the lattice in plan view is not limited. Examples of the shape of the unit structure of the lattice in plan view include a triangular shape (triangular lattice), a square shape (square lattice), a hexagonal shape (hexagonal lattice) and the like. In the present embodiment, the shape of the unit structure of the lattice is square (square lattice) in plan view. Lattice-like protrusion line  130  includes a plurality of first protrusion lines  133 , and a plurality of second protrusion lines  135 . First protrusion line  133  and second protrusion line  135  have the same shape, and therefore first protrusion line  133  is described below. 
         [0045]    First protrusion lines  133  on rear surface  122  extend in the first direction, and are arranged in the second direction perpendicular to the first direction. The distance between first protrusion lines  133  adjacent to each other in the second direction is not limited. In the present embodiment, first protrusion lines  133  adjacent to each other in the second direction are arranged with no gap therebetween. The cross-sectional shape of first protrusion line  133  in the direction orthogonal to the extending direction is not limited as long as diffuse reflection of light reaching first protrusion line  133  can be caused. Examples of the cross-sectional shape of first protrusion line  133  in the second direction include a triangular shape, a triangular shape with a rounded apex, a semicircular shape and the like. In the present embodiment, the cross-sectional shape of first protrusion line  133  in the second direction is a triangular shape. In addition, first ridgeline  134  of first protrusion line  133  is a straight line. It is to be noted that the groove formed by first protrusion lines  133  adjacent to each other may have a round shape. 
         [0046]    Second protrusion lines  135  on rear surface  122  extend in the second direction, and are arranged in the first direction. Thus first protrusion lines  133  and second protrusion lines  135  are disposed such that first ridgeline  134  and second ridgeline  136  are perpendicular to each other. Accordingly, a plurality of recesses having a square pyramid shape are formed at the portions surrounded by first protrusion lines  133  and second protrusion lines  135 . 
         [0047]    Preferably, lattice-like protrusion line  130  is as fine as possible in a range allowing metal mold working for injection molding, and appropriate transferring of the shape of the metal mold in injection molding. It is to be noted that, preferably, the surface of lattice-like protrusion line  130  is properly roughened. To be more specific, when the Rz (maximum height) based on JIS B 0601-2001 is about 10 μm, a proper diffusion effect can be achieved while maintaining the effect of lattice-like protrusion line  130 . To achieve such a roughening effect, the Rz (maximum height) is preferably 5 μm to 30 μm. 
         [0048]    The region in which lattice-like protrusion line  130  is formed is not limited. Lattice-like protrusion line  130  may not be formed on the entire rear surface  122 . It suffices that lattice-like protrusion line  130  is formed in a region where light from light emitting element package  110  at a large emission angle to light axis LA easily reaches. 
         [0049]    The method for forming lattice-like protrusion line  130  is not limited. Lattice-like protrusion line  130  may be integrally shaped by injection molding as a part of light flux controlling member  120 , or may be shaped by knurling or the like after light flux controlling member  120  is formed. 
         [0050]    Annular groove  140  on rear surface  122  is formed outside lattice-like protrusion line  130  with respect to light axis LA. Annular groove  140  reflects, in the lateral direction (outside in the radial direction with respect to central axis CA), a part of light incident on incidence surface  121 , which is internally reflected by emission surface  123  toward rear surface  122 . In the cross section including central axis CA, annular groove  140  has a V-like shape. Annular groove  140  includes internal slope surface  141  disposed on light axis LA (central axis CA) side, and external slope surface  142  disposed on the outside relative to internal slope surface  141 . 
         [0051]    Internal slope surface  141  is disposed to surround central axis CA (light axis LA). In the cross section including central axis CA, internal slope surface  141  is disposed along central axis CA. 
         [0052]    In external slope surface  142 , a plurality of protrusions  143  are formed. Each protrusion  143  is formed in a nearly triangular cross sectional shape, and is rotationally symmetrical about (n-fold rotational symmetry where n is the number of protrusion  143 ) central axis CA. Each protrusion  143  includes first slope surface  144  having a planar shape, second slope surface  145  having a planar shape, and third ridgeline  146  that is an intersection line of first slope surface  144  and second slope surface  145 . Each protrusion  143  functions as a total reflection prism. As illustrated in  FIG. 1 , in a cross section of light flux controlling member  120  including light axis LA and third ridgeline  146 , light axis LA and third virtual line L 3  including third ridgeline  146  intersect each other at a position remote from rear surface  122  relative to external slope surface  142  in the light axis direction. That is, each protrusion  143  is tilted at a predetermined angle (for example) 60° with respect to central axis CA such that the front side is closer to central axis CA than the rear side (light emitting element package  110  side). Here, the “light axis direction” is the travelling direction of light emitted from light emitting element  112 . 
         [0053]    As described above, annular groove  140  reflects in the lateral direction (outside in the radial direction with respect to central axis CA) light which is reflected by emission surface  123  toward rear surface  122 . At this time, light reaching annular groove  140  is sequentially reflected by first slope surface  144  and second slope surface  145  of protrusion  143  toward the lateral direction. The light reflected by annular groove  140  is emitted from flange part  124 , for example. 
         [0054]    The position of annular groove  140  is not limited, and preferably, annular groove  140  is formed in a region where a large quantity of light reflected by emission surface  123  arrives. The arrival position of the light reflected by emission surface  123  differs depending on various factors such as the shape of emission surface  123 , and therefore is appropriately set in accordance with light flux controlling member  120 . 
         [0055]    It is to be noted that the positions in the direction of central axis CA of a part of rear surface  122  having a planar shape located between lattice-like protrusion line  130  and annular groove  140 , and the other part of rear surface  122  having a planar shape located on radially outside relative to annular groove  140  are not limited. The part of rear surface  122  having a planar shape on the inside of annular groove  140 , and the other part of rear surface  122  having a planar shape on the outside of annular groove  140  may be disposed at the same position, or different positions in the direction of central axis CA. In the present embodiment, the parts are disposed at the same position (height) in the direction of central axis CA. 
         [0056]      FIG. 4  is a drawing for describing a positional relationship between each of the four sides of the outer edge of light emitting element  112 , and lattice-like protrusion line  130 . It is to be noted that  FIG. 4  schematically illustrates a plan view of only light emitting element  112 , recess  127 , first ridgeline  134  and second ridgeline  136 . 
         [0057]    As illustrated in  FIG. 4 , light emitting element package  110  and light flux controlling member  120  are disposed such that smaller angle θ 1  between each of the four sides of the outer edge of light emitting element package  110  and first virtual line L 1  parallel to the ridgelines of lattice-like protrusion line  130  (first ridgeline  134  of first protrusion line  133  and second ridgeline  136  of second protrusion line  135 ) is an acute angle. In the present embodiment, light emitting element package  110  and light flux controlling member  120  are disposed such that smaller angle θ 1  between each of the four sides of the outer edge of light emitting element package  110  and first virtual line L 1  is 45°. 
       (Effect) 
       [0058]    Since smaller angle θ 1  between each of the four sides of the outer edge of light emitting element package  110  and first virtual line L 1  parallel to the ridgelines of lattice-like protrusion line  130  (first ridgeline  134  of first protrusion line  133  and second ridgeline  136  of second protrusion line  135 ) is an acute angle as described above, light emitting device  100  according to the present embodiment can suppress unevenness in illuminance even in the case where light emitting element package  110  and light flux controlling member  120  are close to each other (see  FIG. 17A  to  FIG. 18D ). 
       (Modification) 
       [0059]    It is to be noted that, as illustrated in  FIG. 5A  and  FIG. 5B , a plurality of protrusions  143  may not be formed in annular groove  140 ′ in light flux controlling member  120 ′. In this case, annular groove  140 ′ of light flux controlling member  120 ′ includes internal slope surface  141  and external slope surface  142 ′. Internal slope surface  141  is identical to internal slope surface  141  of light flux controlling member  120  of Embodiment 1. External slope surface  142 ′ is disposed to surround central axis CA (light axis LA). In the cross section including central axis CA, light axis LA and virtual line L 2  including the cross section of external slope surface  142 ′ intersect each other at a position remote from rear surface  122  relative to external slope surface  142 ′ in the light axis direction. 
         [0060]    In addition, each of first protrusion line  133  and second protrusion line  135  illustrated in  FIG. 6A  may have a triangular cross-sectional shape with a rounded apex in the direction perpendicular to the extending direction. Also in this case, as illustrated in  FIG. 6B , a plurality of protrusions  143  may not be formed in annular groove  140 . In addition, although not illustrated in the drawings, it is also possible to round each side of a recess having a square pyramid shape formed by adjacent two first protrusion lines  133  and adjacent two second protrusion lines  135 . 
         [0061]    In addition, although not illustrated in the drawings, a lattice-like recess line may be formed in place of lattice-like protrusion line  130  on rear surface  122 . In this case, the lattice-like recess line includes a plurality of first recess lines, and a plurality of second recess lines. The first recess lines extend in the first direction, and are arranged on rear surface  122  in the first direction perpendicular to the second direction. Examples of the cross-sectional shape of the first recess line in the second direction include a triangular shape, a triangular shape with a rounded apex, a semicircular shape and the like. In addition, the valley line of the first recess line is a straight line. The second recess lines extend in the second direction, and are arranged in the first direction. In addition, examples of the cross-sectional shape of the second recess line in the first direction include a triangular shape, a triangular shape with a rounded apex, a semicircular shape and the like. In addition, the light emitting element package and the light flux controlling member are disposed such that the smaller angle between each of the four sides of the outer edge of light emitting element package  110  and first virtual line L 1  parallel to the valley line of the lattice-like recess line is an acute angle. 
       Embodiment 2 
       [0062]    A light emitting device according to Embodiment 2 is different from light emitting device  100  according to Embodiment 1 only in configuration of lattice-like protrusion line  230  formed on rear surface  222  of light flux controlling member  220 . In view of this, the configurations similar to those of light emitting device  100  according to Embodiment 1 will be denoted with the same reference numerals, and the description thereof will be omitted. 
         [0063]      FIG. 7  is a sectional view of light flux controlling member  220  according to Embodiment 2.  FIG. 8A  is a bottom view of light flux controlling member  220 , and  FIG. 8B  is an enlarged view of a region surrounded the broken line in  FIG. 8A . It is to be noted that, in  FIG. 7 , hatching of the cross section in light flux controlling member  220  is omitted. 
         [0064]    As illustrated in  FIG. 7  to  FIG. 8B , lattice-like protrusion line  230  is formed on rear surface  222  of light flux controlling member  220  according to Embodiment 2. In the present embodiment, the shape of the unit structure of the lattice in plan view is a triangular shape (triangular lattice). Lattice-like protrusion line  230  includes a plurality of third protrusion lines  233 , a plurality of fourth protrusion lines  235 , and a plurality of fifth protrusion lines  237 . It is to be noted that third the configurations of protrusion line  233 , fourth protrusion line  235  and fifth protrusion line  237  are identical to those of first protrusion line  133  and second protrusion line  135 . 
         [0065]    In plan view, third protrusion line  233  extends in a direction which is not parallel to each of the four sides of the outer edge of light emitting element  112 , and is not perpendicular to each of the four sides. On rear surface  222 , fourth protrusion line  235  is disposed in a direction at an angle of 60° with respect to the extending direction of third protrusion line  233  in the plane direction. In addition, on rear surface  222 , fifth protrusion line  237  is disposed in a direction at an angle of 60° with respect to the extending direction of fourth protrusion line  235 . That is, the smaller angle between fourth ridgeline  234  of third protrusion line  233  and fifth ridgeline  236  of fourth protrusion line  235  is 60°, and the smaller angle between fifth ridgeline  236  of the fourth protrusion line and sixth ridgeline  238  of fifth protrusion line  237  is also 60°. Accordingly, a recess having a triangular pyramidal shape is formed in a portion surrounded by third protrusion line  233 , fourth protrusion line  235  and fifth protrusion line  237 . 
         [0066]      FIG. 9  is a drawing for describing a positional relationship between each of the four sides of the outer edge of light emitting element  112  and lattice-like protrusion line  230 . It is to be noted that  FIG. 9  schematically illustrates a plan view of only light emitting element  112 , recess  127 , fourth ridgeline  234 , fifth ridgeline  236  and sixth ridgeline  238 . 
         [0067]    As illustrated in  FIG. 9 , also in Embodiment 2, light emitting element package  110  and light flux controlling member  220  are disposed such that smaller angle θ 1  between each side of the outer edge of light emitting element package  110  and first virtual line L 1  parallel to the ridgelines (fourth ridgeline  234  of third protrusion line  233 , fifth ridgeline  236  of fourth protrusion line  235  and sixth ridgeline  238  of fifth protrusion line  237 ) of lattice-like protrusion line  230  is an acute angle. 
       (Effect) 
       [0068]    With the above-mentioned configuration, the light emitting device according to the present embodiment has an effect similar to that of Embodiment 1. 
       (Modification) 
       [0069]    It is to be noted that, as illustrated in  FIG. 10A  and  FIG. 10B , a plurality of protrusions  143  may not be formed in annular groove  140 ′ in light flux controlling member  220 ′. In this case, annular groove  140 ′ of light flux controlling member  220 ′ includes internal slope surface  141  and external slope surface  142 ′. Internal slope surface  141  is identical to internal slope surface  141  of light flux controlling member  220  of Embodiment  2 . External slope surface  142 ′ is disposed to surround central axis CA (light axis LA). In the cross section including central axis CA, light axis LA and virtual line L 2  including the cross section of external slope surface  142 ′ intersect each other at a position remote from rear surface  222  relative to external slope surface  142 ′ in the light axis direction. 
         [0070]    In addition, as illustrated in  FIG. 11A , each of third protrusion line  233 , fourth protrusion line  235  and fifth protrusion line  237  illustrated in  FIG. 8B  may have a triangular cross-sectional shape with a rounded apex in a direction perpendicular to the extending direction. In addition, although not illustrated in the drawings, the cross section of adjacent side surfaces may be rounded in a cross section of the triangular pyramidal shape parallel to rear surface  222 . Also in this case, as illustrated in  FIG. 11B , a plurality of protrusions  143  may not be formed in annular groove  140 ′. 
         [0071]    In addition, although not illustrated in the drawings, a lattice-like recess line may be formed in place of lattice-like protrusion line  230  on rear surface  222 . In this case, the lattice-like recess line includes a plurality of first recess lines, a plurality of second recess lines, and a plurality of third recess lines. The smaller angle between a fourth valley line of the third recess line and a fifth valley line of the fourth recess line is 60°, and the smaller angle between the fifth valley line of the fourth recess line and the sixth valley line of the fifth recess line is also 60°. Examples of the cross-sectional shape of the first recess line, the second recess line and the third recess line in directions orthogonal to the valley lines include a triangular shape, a triangular shape with a rounded apex, a semicircular shape and the like. In addition, the valley lines of the first recess line, the second recess line and the third recess line are straight lines. In addition, the light emitting element package and the light flux controlling member are disposed such that the smaller angle between each of the four sides of the outer edge of light emitting element package  110  and first virtual line L 1  parallel to the valley line of the lattice-like recess line is an acute angle. 
       Embodiment 3 
       [0072]    A light emitting device according to Embodiment 3 is different from light emitting device  100  according to Embodiment 1 only in configuration of lattice-like protrusion line  330  formed on rear surface  322  of light flux controlling member  320 . In view of this, the configurations similar to those of light emitting device  100  according to Embodiment 1 will be denoted with the same reference numerals, and the description thereof will be omitted. 
         [0073]      FIG. 12  is a sectional view of light flux controlling member  320  according to Embodiment 3.  FIG. 13A  is a bottom view of light flux controlling member  320 , and  FIG. 13B  is an enlarged view of a region surrounded by the broken line in  FIG. 13A . It is to be noted that, in  FIG. 12 , hatching of the cross section in light flux controlling member  320  is omitted. 
         [0074]    As illustrated in  FIG. 12  to  FIG. 13B , lattice-like protrusion line  330  is formed on rear surface  322  of light flux controlling member  320  according to Embodiment 3. The shape of the unit structure of the lattice in plan view in the present embodiment is a substantially quadrangle (whose opposite two sides are straight lines and other opposite two sides are arcs). Lattice-like protrusion line  330  includes a plurality of sixth protrusion lines (annular protrusions)  333 , and a plurality of seventh protrusion lines (radial protrusion lines)  337 . 
         [0075]    Sixth protrusion lines  333  on rear surface  322  are annular protrusions concentrically disposed to surround central axis CA. Sixth protrusion line  333  includes first annular surface  334 , second annular surface  335  and seventh ridgeline  336 . First annular surface  334  is disposed on central axis CA side. In a cross section of light flux controlling member  320  including light axis LA, light axis LA and a virtual line including first annular surface  334  intersect each other at a position separated from rear surface  322  in the light axis direction. Second annular surface  335  is disposed outside first annular surface  334 . In a cross section of light flux controlling member  320  including light axis LA, light axis LA and a virtual line including second annular surface  335  intersect central axis CA (light axis LA) at a position remote from rear surface  322  in the direction opposite to the light axis direction. Seventh ridgeline  336  is an intersection line of first annular surface  334  and second annular surface  335 , and is disposed on a virtual plane including rear surface  322   a.  A predetermined gap may or may not be provided between sixth protrusion lines  333  adjacent to each other. In the present embodiment, sixth protrusion lines  333  adjacent to each other are disposed with no gap therebetween. 
         [0076]    Seventh protrusion line  337  on rear surface  322  is radially disposed around central axis CA. The cross-sectional shape orthogonal to eighth ridgeline  338  of seventh protrusion line  337  is not limited as long as light reaching seventh protrusion line  337  can be diffused. Examples of the cross-sectional shape of seventh protrusion line  337  in the circumferential direction include a triangular shape, a triangular shape with a rounded apex, a semicircular shape and the like. In the present embodiment, seventh protrusion line  337  has a triangular cross-sectional shape in the circumferential direction. In addition, in the present embodiment, the cross-sectional area of seventh protrusion line  337  on central axis CA side (a region around the opening of recess  127 ) is smaller than the cross-sectional area of seventh protrusion line  337  on the external side in the radial direction around central axis CA. The shapes of seventh protrusion lines  337  may be identical to each other or different from each other. In the present embodiment, the shapes of seventh protrusion lines  337  are identical to each other. Eighth ridgeline  338  of seventh protrusion line  337  is a straight line, and disposed on the virtual plane including rear surface  322 . 
         [0077]    The number and installation position of seventh protrusion lines  337  are not limited. In the present embodiment,  36  seventh protrusion lines  337  are provided. In addition,  36  seventh protrusion lines  337  are evenly disposed in the circumferential direction. It is to be noted that the Rz (maximum height) of the surface of lattice-like protrusion line  330  in a region around the opening of recess  127  is about 10 μm. 
         [0078]      FIG. 14  is a drawing for describing a positional relationship between each of the four sides of the outer edge of light emitting element  112  and a lattice-like protrusion line. It is to be noted that  FIG. 14  schematically illustrates a plan view of only light emitting element  112 , recess  127 , seventh ridgeline  336  and eighth ridgeline  338 . 
         [0079]    As illustrated in  FIG. 14 , light emitting element package  110  and light flux controlling member  320  are disposed such that smaller angle θ between each of the four sides of the outer edge of light emitting element  112  and first virtual line L 1  parallel to the ridgelines (seventh ridgeline  336  of sixth protrusion line  333  and eighth ridgeline  338  of seventh protrusion line  337 ) of lattice-like protrusion line  330  is an acute angle. 
       (Effect) 
       [0080]    With the above-mentioned configuration, the light emitting device according to the present embodiment has an effect similar to that of Embodiment 1. 
       (Modification) 
       [0081]    It is to be noted that, as illustrated in  FIG. 15A  and  FIG. 15B , a plurality of protrusions  143  may not be formed in annular groove  140 ′ in light flux controlling member  320 ′. In this case, annular groove  140 ′ of light flux controlling member  320 ′ includes internal slope surface  141  and external slope surface  142 ′. Internal slope surface  141  is identical to that of Embodiment 2. External slope surface  142 ′ is disposed to surround central axis CA (light axis LA). In the cross section including central axis CA, light axis LA (central axis CA) and virtual line L 2  including the cross section of external slope surface  142 ′intersect each other at a remote position relative to external slope surface  142 ′ in the light axis direction. 
         [0082]    In addition, as illustrated in  FIG. 16A , sixth protrusion line  333  and seventh protrusion line  337  illustrated in  FIG. 13B  may have a triangular cross-sectional shape with a rounded apex in a direction perpendicular to the extending direction. Also in this case, as illustrated in  FIG. 16B , a plurality of protrusions  143  may not be formed in annular groove  140 ′. 
         [0083]    In addition, although not illustrated in the drawings, lattice-like recess line  330  may be formed in place of lattice-like protrusion line on rear surface  322 . In this case, lattice-like recess line includes a plurality of sixth recess lines, and a plurality of seventh recess lines. Sixth recess line may have a first annular surface, a second annular surface and a seventh ridgeline. First annular surface is disposed on central axis CA side. In a cross section of light flux controlling member  320 ′ including light axis LA, light axis LA (central axis CA) and a virtual line including the first annular surface intersect central axis CA (light axis LA) at a position remote from rear surface  322  relative to emission surface  123  in the light axis direction. The second annular surface is disposed outside the first annular surface. In a cross section of light flux controlling member  320 ′ including light axis LA, light axis LA and a virtual line including the second annular surface intersect each other at a position separated from rear surface  322  in a direction opposite to the light axis direction. Seventh ridgeline  336  is an intersection line of the first annular surface and the second annular surface, and is disposed on a virtual plane including the rear surface. Seventh recess line on the rear surface is radially disposed around central axis CA. Seventh protrusion line  337  may have a triangular cross-sectional shape in the circumferential direction. In addition, in the present embodiment, the cross-sectional area of the seventh recess line on central axis CA side (a region around the opening of recess  137 ) is smaller than the cross-sectional area of the seventh recess line on the outside in the radial direction around central axis CA. The eighth ridgeline of the seventh recess line is a straight line, and is disposed on a virtual plane including rear surface  322 . 
       (Illuminance Distribution of Light Emitting Device) 
       [0084]    Next, the light distribution characteristics of the light emitting devices according to Embodiments 1 to 3 were examined To be more specific, the illuminance on an illumination surface which is disposed over light emitting element package  110  in parallel to the light emitting surface of light emitting element package  110  with an air layer therebetween was measured. In the measurement, the distance between the surface of substrate  150  and the illumination surface (400 mm×400 mm) is 19 mm, and the light flux controlling member has a diameter of 19 mm In addition, in the measurement, the number of light emitting element package  110  and light flux controlling members  120 ,  220 , and  320  is one. In addition, for comparison, the illuminance on the illumination surface was measured also with light flux controlling member  420  (also referred to as light flux controlling member  420  of Comparative example 1) in which the maximum height (Rz) is 60 μm, and the angle between each of the four sides of the outer edge of light emitting element  112  and first virtual line L 1  is 90°, and light flux controlling member  520  (also referred to as light flux controlling member  520  of Comparative example 2) in which the maximum height (Rz) is 10 μm, and the smaller angle between each of the four sides of the outer edge of light emitting element  112  and first virtual line L 1  is an acute angle. 
         [0085]      FIG. 17A  to  FIG. 19B  are graphs illustrating the light flux controlling members used for the measurement and measurement results.  FIG. 17A  is a bottom view of light flux controlling member  420  according to Comparative example 1,  FIG. 17B  shows a measurement result obtained with light flux controlling member  420  according to Comparative example 2,  FIG. 17C  is a bottom view of light flux controlling member  520  according to Comparative example 2, and  FIG. 17D  shows a measurement result obtained with light flux controlling member  520  according to Comparative example 2.  FIG. 18A  is a bottom view of light flux controlling member  120  according to Embodiment 1,  FIG. 18B  shows a measurement result obtained with light flux controlling member  120  according to Embodiment 1,  FIG. 18C  is a bottom view of light flux controlling member  220  according to Embodiment 2, and  FIG. 18D  shows a measurement result obtained with light flux controlling member  220  according to Embodiment 2.  FIG. 19A  is a bottom view of light flux controlling member  320  according to Embodiment 3, and  FIG. 19B  shows a measurement result obtained with light flux controlling member  320  according to Embodiment 3. 
         [0086]    It is to be noted that the illuminance distributions illustrated in  FIG. 17B ,  FIG. 17D ,  FIG. 18B  and  FIG. 18D  are corrected to emphasize the contrast on the illumination surface. Here, the method of the correction is described. In the correction, the average value of the brightness of pixels in a predetermined range around a given pixel of the obtained digital image was set to the brightness of the given pixel. This correction was performed on all pixels of the digital image. By performing this correction for all pixels in the above-mentioned manner, the contrast of the digital image can be increased. 
         [0087]    As illustrated in  FIG. 17A  to  FIG. 17D , illuminance unevenness was caused in the light emitting devices which include light flux controlling members  420  and  520  according to Comparative examples 1 and 2 in which each of the four sides of the outer edge of light emitting element package  110  and a virtual line parallel to the ridgeline of the lattice-like protrusion line formed on rear surface  122  are parallel or orthogonal to each other. In particular, as illustrated in  FIG. 17B , in the light emitting device including light flux controlling member  420  according to Comparative example 1 illustrated in  FIG. 17A , illuminance unevenness of a petal-like shape was caused at a position about 40 mm from the center (the center portion in  FIG. 19B ) of the light emitting surface. 
         [0088]    On the other hand, as illustrated in  FIG. 18A  to  FIG. 19B , illuminance unevenness was suppressed in the light emitting devices which include light flux controlling members  120 ,  220 , and  320  according to Embodiments 1 to 3 in which the smaller angle between each of the four sides of the outer edge of light emitting element package  110  and a virtual line parallel to the ridgeline of lattice-like protrusion line  130 ,  230 , or  330  formed on rear surface  122 ,  222 , or  322  is an acute angle. 
         [0089]    In light flux controlling members  120 ,  220 , and  320  according to Embodiments 1 to 3, the sizes of first protrusion line  133  and second protrusion line  135  (square pyramid recess) are small in comparison with light flux controlling member  420  of Comparative example 1 as described above, and therefore the light which causes the illuminance unevenness of a petal-like shape of light flux controlling member  420  of Comparative example 1 is not easily generated. In addition, light flux controlling members  120 ,  220 , and  320  according to Embodiments 1 to 3 are disposed such that the smaller angle between each of the four sides of the outer edge of light emitting element package  110  and the virtual line is an acute angle, and thus the illuminance unevenness of a petal-like shape is not caused even when the light which causes the illuminance unevenness of a petal-like shape of light flux controlling member  420  of Comparative example 1 is generated. Since the size of the slope surface where the light travelling in the light flux controlling member can possibly arrive can be set to a small value with a lattice-like protrusion line in comparison with a lattice-like recess line, it is possible to suppress internal reflection and reduce the light which causes the illuminance unevenness of a petal-like shape with a lattice-like protrusion line in comparison with a lattice-like recess line. 
         [0090]    This application is entitled to and claims the benefit of Japanese Patent Application No. 2014-248086 filed on Dec. 8, 2014, the disclosure each of which including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0091]    The light emitting device according to the embodiments of present invention can be applied as a light source of a backlight of a liquid crystal display apparatus, signs, generally-used illumination apparatuses, and the like, for example. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  Light emitting device 
           110  Light emitting element package 
           111  Package substrate 
           112  Light emitting element 
           113  Cavity 
           114  Internal surface 
           120 ,  120 ′,  220 ,  220 ′ 320 ,  320 ′,  420 ,  520  Light flux controlling member 
           121  Incidence surface 
           122 ,  222 ,  322  Rear surface 
           123  Emission surface 
           123   a  First emission surface 
           123   b  Second emission surface 
           123   c  Third emission surface 
           124  Flange part 
           125  Leg part 
           126  Protrusion 
           127  Recess 
           130 ,  230 ,  330  Lattice-like protrusion line 
           133  First protrusion line 
           134  First ridgeline 
           135  Second protrusion line 
           136  Second ridgeline 
           140 ,  140 ′ Annular groove 
           141  Internal slope surface 
           142 ,  142 ′ External slope surface 
           143  Protrusion 
           144  First slope surface 
           145  Second slope surface 
           146  Third ridgeline 
           150  Substrate 
           233  Third protrusion line 
           234  Fourth ridgeline 
           235  Fourth protrusion line 
           236  Fifth ridgeline 
           237  Fifth protrusion line 
           238  Sixth ridgeline 
           333  Sixth protrusion line 
           334  First annular surface 
           335  Second annular surface 
           336  Seventh ridgeline 
           337  Seventh protrusion line 
           338  Eighth ridgeline