Lighting and/or signalling device for an automobile

The device has a light source (1) for emitting a light beam, and an optical guide (3) allowing propagation of the light beam into the guide. The guide includes a light exit face and a set of optical reflection patterns (20) for reflection of directed fractions (17) from the light beam through the exit face according to a preferred direction. The guide includes a set of optical diffusion patterns (22) for diffusion of diffused fractions (19) from the light beam through the exit face. Reflection patterns are alternated with the diffusion patterns.