Patent ID: 8011802

Claim:
A lighting device comprising: a plurality of point light sources arranged in plane with each other; and an optical sheet arranged in a region facing the plurality of point light sources, wherein the plurality of point light sources are arranged in a first direction and also in a second direction intersecting with the first direction, and the optical sheet has a tridimensional configuration that includes a first ridgeline extending in a third direction intersecting with the first and second directions, and a second ridgeline extending in a direction intersecting with the first, second and third directions, wherein the optical sheet includes a pair of first slant faces opposed each other with the first ridgeline in between and a pair of second slant faces opposed each other with the second ridgeline in between, and inclinations of the respective first and second slant faces are determined so that an arm length D of each X-shaped light source image, which is obtained by dividing a light source image produced from a light emitted from each of the plurality of point light sources into plural images through the optical sheet, satisfies the following expression when a pitch of the point light sources is defined as P: D≧P/ 2.