Patent ID: 8870434

Claim:
A planar light guide film for a backlight unit having at least one point light source, the light guide film comprising: a light input surface for receiving light from the point light source; a light redirecting surface for redirecting light received from the light input surface; a light output surface for outputting at least the light redirected from the light redirecting surface; wherein the light input surface further comprises a composite lens structure having a first and second circular tip segment each circular tip segment with a first contact angle, and a first and second circular base segment each circular base segment with a top and bottom contact angle, the contact angles of the circular base segments being less than the contact angle of the circular tip segments; and wherein the first and second circular tip segments satisfies the following equations: y 1 =a 1 +√{square root over (( r 1 2 −x 2 ))} y 2 =a 2 +√{square root over (( r 2 2 −x 2 ))} wherein x is a value in a direction of the light input surface, y 1 is a value in a light propagation direction, r 1 is a radius of the first circular tip segment, a 1 is a y-coordinate of a center of the first circular tip segment, y 2 is a value in the light propagation direction, r 2 is a radius of the second circular tip segment, a 2 is a y-coordinate of a center of the second circular tip segment, and the first and second circular base segments satisfies the following equations: y 3 =b 3 −√{square root over (( r 3 2 −( x+a 3 ) 2 ))} y 4 =b 4 −√{square root over (( r 4 2 −( x−a 4 ) 2 ))} wherein y 3 is a value in the light propagation direction, r 3 is a radius of the first circular base segment, a 3 and b 3 are x- and y-coordinates respectively of a center of the first circular base segment, y 4 is a value in the light propagation direction, r 4 is a radius of the second circular base segment, and a 4 and b 4 are x- and y-coordinates respectively of a center of the second circular base segment, and each of the composite lens structures is randomly disposed along the light input surface.