In the invention, a comparison is carried out within a computer of an item of
information relating to a direction of a light beam of a lamp, this item of information
being obtained by means of a position sensor, and an item of information relating
to an instruction for horizontal displacement of the light beam. If there is not
agreement between the two items of information, the computer can then have a degraded
operating mode of the lamp adopted by compelling it to orient the light beam downwards
in order to remove any risk of dazzling an oncoming driver. To that end, the computer
controls a range correction motor in order to bring about a downwards vertical
deviation of the light beam.
