the chamber 1 and inside a duct 20 fig3 b this duct 20 comprises an air inlet 22 positioned under the casing 5 and an air outlet 23 when the vehicle is moving air will be swept inside the duct 20 through the inlet 22 and will leave in the region of the outlet 23 of the duct the heat dissipated inside the chamber 1 is transferred from inside the chamber to outside the chamber by the heat exchanger 16 and circulation of air over the vanes 17 will evacuate heat emitted by the heat exchanger 16 although the duct 20 can emerge directly into the engine compartment the outlet 23 is preferably connected to an air duct leading the air directly from the duct to an air outlet not shown of the body of the vehicle since fig1 and 2 are schematic representations they equally apply to two embodiments of the duct according to one of these embodiments the duct 20 is incorporated in the headlight according to another embodiment part of the inner wall of the duct 20 consists of a part 15 16 and 14 fig3 c of the outer wall of the casing 5 and a part 26 of the inner wall of the duct consists of an element of the vehicle body the space between the part 26 and the part 15 16 and 14 constituting the interior of the duct 20 it is also possible according to an embodiment not shown to produce a duct that is a part incorporated in the vehicle and that is in contact with a heat exchanger of the casing of the headlight as shown in fig1 the part of the casing that is not in contact.