Are you allowed to use the headlights in this situation?

Using main beam headlights (full beams) is prohibited in this situation because they could dazzle the driver of the preceding vehicle by reflecting in their mirrors. According to Art. 51 para. 3 of the Road Traffic Act, you must switch from main beam to dipped beam headlights when you are approaching a vehicle travelling in front of you in the same direction. You should keep your dipped beams on until you have safely overtaken that vehicle.