Surface light source device, display device and light flux controlling member

A surface light source device comprising:

• a plurality of light-emitting devices disposed on an XY plane of an XYZ coordinate that defines an X direction, a Y direction and a Z direction orthogonal to each other;
• and
• a light diffusion plate disposed at a distance from the XY plane in the Z direction,
• wherein each of the plurality of light-emitting devices includes a light-emitting element and a light flux controlling member configured to control light from the light-emitting element,
• wherein the light flux controlling member includes an incidence surface from which light from the light-emitting element enters, a total reflection surface configured to reflect a part of light entered from the incidence surface, and an emission surface disposed at a periphery of the total reflection surface,
• wherein the light flux controlling member has an ellipse shape with a major axis in the Y direction and a minor axis in the X direction in plan view and bottom view of the light flux controlling member,
• wherein the incidence surface is an inner surface of a recess disposed on a rear side of the light flux controlling member, and the incidence surface has an ellipse shape with a minor axis in the Y direction and a major axis in the X direction in bottom view of the light flux controlling member,
• wherein the emission surface includes a curved surface that slopes downward in the Z direction toward an outer periphery of the light flux controlling member,
• wherein one or more of the plurality of light-emitting devices are arranged in a line in the X direction and one or more of the plurality of light-emitting devices are arranged in a line in the Y direction, and Py>Px holds, where Px represents a center-to-center distance of adjacent light-emitting devices among the one or more of the plurality of light-emitting devices arranged in the X direction, and Py represents a center-to-center distance of adjacent light-emitting devices among the one or more of the plurality of light-emitting devices arranged in the Y direction,
• wherein when a line extending along an optical axis OA of a light-emitting element of a given light-emitting device among the plurality of light-emitting devices is set as a reference line L1, an intersection of the reference line L1 and a light arrival plane located on the light-emitting device side of the light diffusion plate is set as a first reference point P1, and an angle of light emitted from the light-emitting element along the reference line L1 is set as 0°, a position where a light beam corresponding to a maximum luminous intensity peak in a graph illustrating light distribution characteristics on a YZ cross section for light emitted at emission angles between 0° and 90° from the light-emitting element, the maximum luminous intensity peak being determined from luminous intensity values measured for the light emitted at emission angles between 0° and 90°, reaches on the light arrival plane is within a range from Py/3 to Py from the first reference point P1, the range being measured along the light arrival plane from the first reference point P1 to the position,
• wherein light that is emitted from the given light-emitting element, reflected by the total reflection surface, and reached the emission surface is emitted from the emission surface at an angle larger than 90° with respect to the reference line L1,
• wherein when an intersection of the reference line L1 and the XY plane is set as a second reference point P2, and a rectangle with a side of a length Px along the X direction and a side of a length Py along the Y direction on the XY plane with the second reference point P2 as a vertex is divided by a diagonal line of the rectangle passing through the second reference point P2 into a triangular region A with the second reference point P2 located at an endpoint of the side with the length Px and a triangular region B with the second reference point P2 located at an endpoint of the side with the length Py, a greater amount of light reaches the triangular region B than the triangular region A when an arrival amount of light defined as a number of light rays reaching the light arrival plane after reflection by the total reflection surface is compared between the triangular region A and the triangular region B,
• wherein in a graph representing a luminance distribution of luminance variation on a straight line extending along the Y direction and passing through the second reference point P2 for light reflected by the total reflection surface and reaching the XY plane, (A) a position in the Y direction of a luminance peak top is located at a position farther from the second reference point than a distance D between an outer edge of the light flux controlling member and a center of the light flux controlling member along the Y direction, or (B) when a line segment corresponding to a half width of a luminance peak is divided into a first division segment W1 nearer to the reference line L1 than the peak top in the Y direction and a second division segment W2 farther from the reference line L1 than the peak top in the Y direction, a length of the second division segment W2 is 1.5 times or greater than a length of the first division segment W1.