Patent ID: 6222689
Filing Date: 2001-04-24
Classification: G02B

Abstract:
A surface light source device comprising:a directional emission guide plate;a primary light source to supply light to an incidence surface located at a side end of said guide plate; andan asymmetric prism sheet disposed along a front surface of said guide plate,wherein said asymmetric prism sheet has a prismatic inner face provided with a plurality of prism element rows running generally parallel to said incidence surface and an uneven outer face,the prism element rows of said prismatic inner face have an alternating first slope facing to said incidence surface and second slope facing opposite to said incidence surface, andsaid first slope and said second slope have inclinations selected so that a main ray emitted from said guide plate is led into said asymmetric prism sheet through said first slope to be deflected toward a first approximately frontal direction by way of internal reflection of said second slope while a secondary ray, which has been emitted from said guide plate with an emission angle greater than that of the main ray, is led into said asymmetric prism sheet through said first slope to be deflected toward a second approximately frontal direction by way of internal reflection of said first slope following after the internal reflection of the second slope.