CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of Japanese Patent Application No. 2020-193521, filed on Nov. 20, 2020, the disclosure of which including the specification, drawings and abstract is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a light flux controlling member that controls the distribution of light emitted from a light-emitting element, a light-emitting device including the light flux controlling member, a surface light source device including the light-emitting device, and a display device including the surface light source device.

BACKGROUND ART

In recent years, in transmissive image display devices such as liquid crystal display devices, direct surface light source devices including a plurality of light-emitting elements as a light source are used. In addition, in some direct surface light source devices, a large number of light-emitting elements are disposed for the purpose of wide irradiation of light.

PTL 1 discloses a surface light source device including a light-emitting element disposed on a substrate and provided with a light-emitting surface with a predetermined size, and a light flux controlling member, and a diffusion member. The light flux controlling member includes an incidence surface for allowing incidence of light emitted from the light-emitting element, a reflecting surface that reflects a part of the light entered from the incidence surface in the direction along the substrate and transmits the other part of the light, and an emission surface that emits the light reflected by the reflecting surface. The reflecting surface reflects, in the direction along the substrate, the light emitted from the vicinity of the center of the light-emitting surface and entered from the incidence surface. On the other hand, a part of light emitted from a region apart from the center of the light-emitting surface and entered from the incidence surface is not reflected by the reflecting surface, but is emitted from the reflecting surface to the outside of the light flux controlling member.

In the surface light source device disclosed in PTL 1, the light emitted from light-emitting element is spread by the light flux controlling member to illuminate a wide range of the diffusion member. The light emitted from the light flux controlling member is further diffused by the diffusion plate. Thus, the surface light source device disclosed in PTL 1 can uniformly illuminate the planar display member (such as a liquid crystal panel).

CITATION LIST

Patent Literature

PTL 1US Patent Application Publication No. 2014/167594

SUMMARY OF INVENTION

Technical Problem

In recent years, light-emitting elements whose light-emitting surface is smaller than the light-emitting surface of known light-emitting elements have been developed. When a light-emitting element with a small light-emitting surface is applied to the surface light source device disclosed in PTL 1, the majority of the light emitted from the light-emitting element is reflected by the reflecting surface and the amount of the light transmitted through the reflecting surface is reduced, and consequently, the display member may not be uniformly illuminated due to the resulting dark points in the region immediately above the light flux controlling member.

An object of the present invention is to provide a light flux controlling member that can suppress luminance unevenness even in the case where the light-emitting surface of the light-emitting element is small. In addition, another object of the present invention is to provide a light-emitting device including the light flux controlling member, a surface light source device including the light-emitting device and a display device including the surface light source device.

Solution to Problem

A light flux controlling member according to an embodiment of the present invention is configured to control a distribution of light emitted from a light-emitting element disposed on a substrate, the light flux controlling member includes: a first optical surface disposed facing the light-emitting element and configured to allow incidence of light emitted from the light-emitting element; a second optical surface disposed on a side opposite to the light-emitting element with the first optical surface between the second optical surface and the light-emitting element, and configured to reflect, in a lateral direction, a part of light entered from the first optical surface such that the part of light entered from the first optical surface travels away from an optical axis of the light-emitting element; a third optical surface where a part of light reflected by the second optical surface reaches; and a fourth optical surface extending in a direction away from the first optical surface to surround the first optical surface, the fourth optical surface being a surface where a part of light reflected by the third optical surface reaches. A part of light emitted from the light-emitting element and entered from the first optical surface is emitted from the second optical surface to outside of the light flux controlling member after being sequentially internally reflected by the second optical surface, the third optical surface and the fourth optical surface. A part of light emitted from the light-emitting element that is incident on the first optical surface is Fresnel-reflected, reflected by a surface of the substrate toward the first optical surface to enter the light flux controlling member from the first optical surface, and then emitted from the second optical surface to the outside of the light flux controlling member.

A light-emitting device according to an embodiment of the present invention includes: a light-emitting element disposed on a substrate; and the light flux controlling member according to an embodiment of the present invention disposed over the light-emitting element.

A light-emitting device according to an embodiment of the present invention includes: a plurality of light-emitting elements disposed on a substrate; and the light flux controlling member according to an embodiment of the present invention disposed over the plurality of light-emitting elements.

A surface light source device according to an embodiment of the present invention includes: a plurality of the light-emitting devices according to an embodiment of the present invention; and a light diffusion plate configured to transmit light emitted from the plurality of light-emitting devices while diffusing the light emitted from the plurality of light-emitting devices.

A display device according to an embodiment of the present invention includes: the surface light source device according to an embodiment of the present invention; and a display member configured to be irradiated with light emitted from the surface light source device.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a light flux controlling member that can suppress luminance unevenness even in the case where the light-emitting surface of the light-emitting element is small. In addition, according to the present invention, it is possible to provide a light-emitting device, a surface light source device, and a display device including the light flux controlling member.

