the mirror 5 is directed onto the lens 3 which gives an illumination grid corresponding to the image of the mirror 5 fig3 illustrates a variant embodiment according to which the shield 1 a is mounted so as to move in vertical translation and the reflecting mirror 5 a is connected to the shield 1 a by vertical sliding the shield 1 a can come into the active position illustrated in a broken line in this same figure by upward translation movement the shield 1 a is placed in an inactive position whilst the reflecting mirror 5 a is placed in the working position illustrated in a solid line which passes exactly through the focus of the lens 3 in a variant the shield 1 could be mounted so as to move in rotation about a vertical axis whilst the reflecting mirror would be offset angularly with respect to the shield whilst being connected to the shield in the rotation movement so that for a first angular position the shield would be in an active position and the reflecting mirror in a retracted position whilst in another angular position the shield would be in an inactive position and the reflecting mirror in the working position the functioning of the optical module of fig3 is as follows when the driver demands the production of the.