Patent ID: 8439548

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 circular tip segment with a first contact angle, and a first and second circular base segments with a second contact angle, the second contact angle being greater than the first contact angle and the second contact angle being equal to each other; and wherein the circular tip segment satisfies the following equation: y 1 =a 1 +√{square root over (( r 1 2 −x 2 ))} and the circular base segments satisfies the following equations: y 2 =b 2 +√{square root over (( r 2 2 −( x+a 2 ) 2 ))} y 3 =b 3 +√{square root over (( r 3 2 −( x−a 3 ) 2 ))}.