Patent ID: 8749731

Claim:
A lighting device comprising: a light source; a light guide plate; a first prism sheet which is arranged over the light guide plate; and a second prism sheet which is arranged between the first prism sheet and the light guide plate, wherein the first prism sheet includes first prisms which are formed parallel to each other in a first direction on a first surface which is opposite to the second prism sheet; the first prism formed on the first prism sheet includes a first inclined surface and a second inclined surface which respectively extend in a second direction which intersects the first direction; light which is emitted from the light source, enters the light guide plate through a side surface of the light guide plate, and is radiated from an upper surface of the light guide plate as a first light, and light which enters the light guide plate through the upper surface of the light guide plate and is radiated from the upper surface of the light guide plate as a second light; the second prism sheet includes second prisms which convert the first light into a third light whose light quantity has the distribution where a magnitude of light quantity is periodically changed at a pitch of the first prisms formed on the first prism sheet in the first direction and allow the third light to be incident on the first prism sheet; the first prism sheet, upon impingement of the third light on the first inclined surfaces, reflects the third light toward a second-inclined-surface side on the first inclined surfaces thus reflecting at least a portion of the third light toward a light-guide-plate side on the second inclined surface; the first prism sheet, upon impingement of the third light on the second inclined surfaces without via the first inclined surfaces, radiates the third light toward the first surface; and the first prism sheet is displaceable between a first state in a wide viewing angle mode where a rate that the third light impinges on the second inclined surfaces without via the first inclined surfaces is smaller than a rate that the third light impinges on the first inclined surface and a second state in a narrow viewing angle where the rate that the third light impinges on the second inclined surfaces without via the first inclined surfaces is larger than the rate that the third light impinges on the first inclined surfaces.