Abstract: A rear-light assembly for a motor vehicle is positioned at a transition from a rear surface (11) to a side surface (12) of the motor vehicle. A light diffuser thereof (1,2) has an exterior surface which extends relatively smoothly into the rear and side surfaces of the rest of the body of the motor vehicle. Light-diffuser portions (17, 18 and 19) for a brake-light reflector (6), a taillight reflector (7), and a fog taillight reflector (8) are provided with linearly arranged exterior-light reflecting rear-beam prisms (20). In a flat area (18, 19) of the light diffuser, which extends over the fog taillight and taillight, the rear-beam prisms are optically effective while at an adjacent area they are made to be optically ineffective. A light-diffuser portion (15) for a backing light reflector (4) is provided with an opaque lattice, or grill, (21, 22) which includes linearly shaped strips (21). This light-diffuser portion is also in an area of the light diffuser which extends substantially planar, or flat.