Patent ID: 8382360

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 y 1 with a first contact angle, and a first and second elliptical base segments y 4 , y 5 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 elliptical base segments satisfies the following equations: y 4 =d 4 +b 4 ×√{square root over ((1−(( x+c 4 )/ a 4 ) 2 )} y 5 =d 5 +b 5 ×√{square root over ((1−(( x−c 5 )/ a 5 ) 2 )}.