in the front of the vehicle or illuminates it only weakly this leads during reflection on a wet roadway to little dazzling of an oppositely approaching vehicle driver for producing the light beam required for illumination of the measuring screen 17 in the above described way the reflectors 13 of the headlights 10 and 11 can be designed so that they reflect the light radiated by the light source 14 and correspondingly the light source 15 so as to produce the light beam alternatively each light beam can be produced by optically active elements on the light disk 16 from the light reflected by the reflector 13 the above described illumination device can be provided in accordance with a further embodiment of the invention with an adjusting device 32 illustrated in fig2 the adjusting device 32 can adjust the headlight 11 which illuminates the opposite traffic side with respect to its inclination the adjusting device 32 can increase the inclination of the headlight 11 to the roadway starting from a value for an unloaded vehicle so that the upper bright dark limit 22 of the light beam radiated by this headlight can assume also for a loaded vehicle the position required for eliminating a dazzling of the opposite traffic it is also possible that the adjusting device 32 can adjust the whole headlight 11 or only its reflector 13 the adjusting device 32 can be operated automatically in this case a control device is provided which detects the loading of the vehicle and sets the adjusting device in operation when an adjustment of the headlight 11 is required to avoid dazzling the opposite traffic it is also.