Patent ID: 7699516

Claim:
A back light structure comprising: a transparent light guide; a light source mounted to direct light into said light guide; and a micro-Fresnel lens array on a surface of said light guide, said micro-Fresnel lens array being shaped to reflect light at an angle such that a portion of the light won't escape from the back light module on a first reflection, and will propagate down said light guide; wherein the micro-Fresnel lenses in the array have a spatial variation described by a function proportional to ( 1 + cos ⁡ ( π ⁡ ( x 2 + y 2 ) λ ⁢ F - 2 ⁢ π λ ⁢ sin ⁢ ⁢ ω ⁢ x ) ) , where parameters ω is larger than the critical angle of the light guide, F is selected to disperse light over an angle less than +/−45 degree and x,y are the spatial coordinates of the Fresnel structure.