A light diffusion device for uniformly dispersing light across a gauge dial plate having indicia associated therewith includes an annular member of transparent or translucent material having front and rear annular surfaces each merging with an outer peripheral surface and an inner peripheral surface....http://www.google.fr/patents/US7553037?utm_source=gb-gplus-shareBrevet US7553037 - Light diffusion device for a gauge dial plate
