Headlamp adaptors are a legal requirement when driving in France and must be applied prior to arrival.
As in the UK we drive on the left hand side of the road, our headlights are designed to shine towards the kerb and away from oncoming vehicles. When we then drive on the right, as in France our headlights automatically shine into the faces of oncoming drivers. Headlight adaptors or beam deflectors are placed at specific points of your light housing to ensure that your headlights don’t shine in the eyes of oncoming traffic and deflect the beam of the light.
If you fail to have them fitted before arrival and are caught out, you could find yourself on the end of a rather hefty on the spot fine.