Patent ID: 8480283

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 y 1 and second y 2 circular tip segments with a first contact angle, and a first y 3 and second y 4 elliptical base segments each with a top and bottom contact angle, the contact angles of the elliptical base segments being less than the contact angles of the circular tip segments and the contact angles of the circular tip segments and elliptical base segments being not equal to each other; and wherein the first and second circular tip segments satisfy the following equations respectively: y 1 =a 1 +√{square root over (( r 1 2 −x 2 ))} y 2 =a 2 +√{square root over (( r 2 2 −x 2 ))} and the first and second elliptical base segments satisfy the following equations respectively: y 3 =d 3 −b 3 ×√{square root over ((1−(( x+c 3 )/ a 3 ) 2 ))} y 4 =d 4 −b 4 ×√{square root over ((1−(( x−c 4 )/ a 4 ) 2 ))} and each of the composite lens structures is randomly disposed along the light input surface.