Light control element, surface light source device and liquid crystal display device

1. A light control element comprising:

a plane of output allowing light to output therethrough; and

a plane of incidence having thereon a number of prism

portions arrayed in parallel, the prism portions having a first prism surface allowing incidence of light and a second prism surface where the light entering through the first prism surface is reflected by total reflection on an inner surface side and to output through the plane of output, wherein a second prism surface is formed as being outwardly swelled in a curved profile being outwardly swelled with a curvature allowing the light to output through the plane of output at a second output viewing angle wider than a first output viewing angle of a case where the second prism surface is flat.

2. The light control element as claimed in claim 1 , wherein:

the prism portion is configured using a virtual prism component as a reference, the virtual prism component having one apex and two bases, a cross section of the virtual prism component being triangular;

the first prism surface is formed along a straight line connecting the apex and one base of the virtual prism component; and

the second prism surface is formed along an arc which passes through the apex and the other base of the virtual prism component.

3. The light control element as claimed in claim 2 ,

wherein the second prism surface satisfies a condition 1.1<R/H≦5.0, where height of the prism portion is H [μm], and

radius of curvature of the second prism surface is R [μm].

4. The light control element as claimed in claim 2 ,

wherein the first prism surface is formed along an arc which passes through the apex and one base of the virtual prism

component.

5. A surface light source device comprising:

a light control element which includes:

a plane of output allowing light to output therethrough, and

a plane of incidence having thereon a number of prism portions arrayed in parallel, the prism portions having a first prism surface allowing incidence of light and a second prism surface where the light entering through the first prism surface is reflected by total reflection on the inner surface side to output the light from the plane of output, the second prism surface having an outwardly-swelled curved profile, formed with a curvature that allows the light to output through the plane of output at a second output viewing angle wider than a first output viewing angle of a case where the second prism surface is flat;

a light guide plate disposed on a side of the plane of incidence of the light control element and made of a translucent material having a side end portion; and

a light source disposed at the side end portion of the light guide plate.

6. A liquid crystal display apparatus comprising:

a light control element which includes:

a plane of output allowing light to output therethrough, and

a plane of incidence having thereon a number of prism portions arrayed in parallel, the prism portions having a first prism surface allowing incidence of light and a second prism surface where the light entering through the first prism surface is reflected by total reflection on the inner surface side to output the light from the plane of output, the second prism surface having an outwardly-swelled curved profile, formed with a curvature that allows the light to output through the plane of output at a second output viewing angle wider than a first output viewing angle of a case where the second prism surface is flat;

a light guide plate disposed on a side of the plane of incidence of the light control element and made of a translucent material having a side end portion;

a light source disposed at the side end portion of the light guide plate; and

a liquid crystal display panel disposed on a side of the plane of output of the light control element.