SURFACE LIGHT SOURCE ELEMENT, AND IMAGE DISPLAY DEVICE AND ILLUMINATING DEVICE USING THE SURFACE LIGHT SOURCE ELEMENT

摘要

A surface light source element is composed of a surface light emitting element (3) and an outputting light control sheet (2), which is arranged on a light outputting surface (13) of the surface light emitting element (3) and has a plurality of protruding sections (10) at least on one surface.  The protruding sections (10) are optically in close contact with the light outputting surface (13) of the surface light emitting element, and the refractive index of a space (11) is lower than that of the protruding section (10).  On the light outputting surface (13) of the surface light emitting element, 80% or more of the side surface of the protruding section (10) satisfies the inequalities of (a1/2)-5°1/2)+11°, where (a1)is an angle with which the value of A(a)×sin(a)×cos(a)is maximum in the case where A(a) is the luminance of a beam which travels at an angle (a) with respect to the normal line of the main surface of the surface light emitting element (3), and (ß) is the tilt angle of the side surface of the protruding section (10) with respect to the normal line of the main surface of the surface light emitting element (3).  Thus, the surface light source element having higher light use efficiency and greatly improved front luminance is obtained.