A light guide including a transparent body which is generally elongated in a principal direction with an outer facet forming a diopter with the environment of the body, a first row of inclined facets adapted to reflect the rays in order for them to exit, and at least one second row of reflecting facets of smaller size than the corresponding reflecting facets of the first row. The light reflected by the second row or rows is added to the light beam coming from the first row. The widths of the first row and the second rows can respectively and progressively increase and decrease from the light source so as to compensate the progressive losses of light traveling in the light guide.