A proposed method to illuminate optimally, or at least in an improved fashion compared with existing solutions, a road taken by a vehicle in question implementing the method whilst ensuring that other vehicles are not dazzled. To this end, it is not proposed in the invention to detect the distance between the vehicle in question and the first vehicle liable to be dazzled by the vehicle in question, and to generate accordingly a light beam optimized in terms of range on the road, and advantageously light intensity; according to the invention, the optimization of the light beam produced is achieved by the use of the motorway function available on the vehicle in question. The use of this function in this context also ensures a gradual transition between the function of the dipped type and the function of the main-beam type in the context of automatic switching operations between these functions.