A light beam forming module, in particular in the vehicle external lighting system, is in the form of a monolithic body formed of a plurality of contiguous cross-sectional segments, each of which includes an entrance surface facing the light source, an exit surface, and a first total internal reflection surface and at least another total internal reflection surface. A first total internal reflection surface is positioned downstream of the entrance surface, and at least one further total internal reflection surface has a shaped optical structure formed thereon.