The invention relates to an optical module of a motor vehicle lighting system, including at least one light source, a primary optical element comprising at least one primary optical member connected to an exit optical member, the primary optical member including a light entry face and a junction face connecting the primary optical member to the exit optical member, the primary optical element being a one-piece component, and an optical projection system designed to project, onto the ground, using light emitted by the light source and collected by the primary optical member, an image of the junction face, the primary optical member being arranged so that the image of its junction face that is projected onto the ground by the optical projection system is entirely bounded by substantially sharp edges.