Patent ID: 8292467

Claim:
An illumination device arranged to generate illumination device light, the illumination device comprising a lighting unit ( 2 ), the lighting unit ( 2 ) comprising: a light source, arranged to generate light source light, and a substantially flat light guide, arranged to collimate the light source light, the light guide having: an entrance window and an edge window, a first light guide surface and a second light guide surface, which are arranged substantially parallel, a first side edge and a second side edge, wherein the first side edge and the second side edge are arranged not to diverge or converge from the entrance window in the direction of the edge window, and wherein the entrance window is arranged to receive the light source light of the light source, wherein the edge window is arranged to allow the collimated light source light escape from the light guide as illumination device light, wherein one or more of the first light guide surface and the second light guide surface comprise a plurality of grooves, and wherein the grooves are arranged to diverge in a direction from the entrance window to the edge window.