The aim of the invention is to reduce the weight and sizes of an electromagnetic retarder for a vehicle by coaxially offsetting said electromagnetic retarder with respect to the transmission of the vehicle, the retarder being provided with a cooling cavity. The lighting apparatus may include two or more lighting units each including a plurality of LED groups which sequentially emit light in response to changes of a rectified voltage. The locking magnet is released from its locking position by an unlatching magnet incorporated in a sealing cap.