The present invention provides 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 and a light output surface for outputting at least the light redirected from the light redirecting surface. 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 elliptical base segments with a second contact angle, the second contact angle being less than the first contact angle and the second contact angle being equal to each other andwherein the circular tip segment satisfies the following equation: y1=a1+√{square root over ((r12−x2))} and the elliptical base segments satisfies the following equations: y4=d4+b4×√{square root over ((1−((x+c4)/a4)2)} y5=d5+b5×√{square root over ((1−((x−c5)/a5)2)}.