Patent ID: 7626655

Claim:
A surface light source device of side light type comprising: a guide plate having a minor face to provide an incidence end face and two major faces to provide an emission face and a back face such that a first edge of the incidence end face abuts a first edge of the emission face along a first direction and the emission face has two substantially parallel edges extending away from the incidence end face in a second direction; and a primary light source providing primary light to the guide plate through the incidence end face, wherein said emission face is provided with a plurality of light scattering elements distributed according to a predetermined pattern such that a covering density of said light scattering elements on the emission face decreases along the first direction according to a distance from each of the two substantially parallel edges, said emission face having a rough area formed on and around said light scattering elements such that the light scattering elements and an area surrounding the light scattering elements are roughened, and said rough area having a roughness degree which is less than that of said light scattering elements.