SURFACE LIGHT SOURCE DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE

摘要

PROBLEM TO BE SOLVED: To provide an edge light type surface light source device with high symmetry of brightness within a light outgoing surface, capable of ensuring a desirable observation angle range without drop in brightness of the surface light source device, and with high light utilization factor. SOLUTION: This surface light source device consists of a light source 1; a lightguide 2 having a light incoming surface 21 facing the light source 1 and a light outgoing surface 28 almost perpendicularly crossing to the light incoming surface 21; and a light direction changing sheet 4 arranged on the light outgoing surface 23 of the lightguide 2. A plurality of prism columns having a vertical angle of 120 deg.-150 deg. extending almost vertically to the light incoming surface 21 are formed in parallel in at least one of the light outgoing surface 23 and the back surface 24 of the lightguide 2.