A light projector intended to produce a directional flat light beam includes an elongate cylindrical lens and a linear light source parallel to the generatrix direction, extending over all or part of the length of the lens to emit light in the direction of the lens. The lens is designed to generate a principal flat light beam by concentrating the light in a predefined elevation angular sector around the horizontal generatrix direction. The light projector also includes a deflector having a rectangular plate shape positioned on the side opposite the light source. A signalling beacon including such a projector is also described.