Lighting or signalling device for vehicle

The present invention relates to a lighting or signaling device for a motor vehicle, comprising at least one light source (20, 20', 20"), a reflector (22) and a light diffusion plate (24). According to the present invention, the reflector (22) and the light diffusion plate (24) are constituted of substantially planar elements forming between them a small and non-zero angle (α, β) and delimiting between them a prismatic volume.