Patent ID: 7338197

Claim:
A flat illumination device (FID), having at least one illumination window defined over at least one plane, comprising: A light guiding plate having at least a front and a back face and at least one edge, said illumination window being outside said light guiding plate; at least one light source, each said light source disposed so as to couple a respective input luminous flux from the light source into a corresponding edge; each input luminous flux forming a corresponding internal flux component which propagates through said light guiding plate by total internal reflection; wherein at least one of said faces is a flux extracting face, which has a pattern of flux extracting elements collecting and extracting said internal flux from all said light sources simultaneously and distributed thereon covering a varying fraction of any elementary area of said flux extracting face in a non-uniform pattern that is substantially a two-dimensional, non-monotonic irregular function of the distance of a point within said elementary area to any point lying on the perimeter of said light guiding plate.