down in order to provide the second main beam function the illumination area illustrated in fig7 comprises above the area 12 an area 14 whose isoluxes have not been shown the secondary reflector 5 in combination with the additional lens 8 contributes to the reinforcement of the illumination of the area 14 and avoids the need for a supplementary main beam headlight when the source s is a halogen source with a single filament the homogeneity and intensity of the beam are improved whatever the light source the transverse offset between the optical axis of the main lens 9 and the additional lens 8 is only a few centimeters and is not noticeable at a distance of 25 m at which the illumination checking screen is generally placed instead of providing the additional lens 8 at the bottom part of the main lens l it could be provided on the right or left side with a corresponding scallop in the main lens however the light beam would be slightly degraded and in addition the right and left headlights of the same vehicle would be different the example embodiment in fig3 to 7 have been given with a single additional lens 8 it would however be possible to provide several hollowed out parts each associated with an additional lens and a corresponding secondary reflector such as 5 fig8 shows a variant embodiment according to which the additional lens 8 a is a divergent lens having for example a front face concave towards the outside the external focus fe 5 of the secondary reflector 5 is situated at the front of the concave face of the lens 8 a merged with or in the vicinity of the focus of this lens.