An apparatus for lighting or indicating purposes in a motor vehicle includes a light guide associated with at least one light source for transporting light rays emitted by the light source from an input face to an output face via and intermediate section of the light guide. The output face of the light guide is contained between two closed lines which define a continuous internal contour and a continuous external contour, and the input face is contained between two further closed lines, also delimiting continuous internal and external contours.