An optical detection system per motor-vehicles, suitable to detect the condition of the road surface on which the vehicle is travelling, comprising a photodetector unit composed of a camera having a matrix of pixels composed of photodetectors based on a photosensitive material suitable to detect both radiations in the visible and near infrared, i.e. having a wavelength comprised between 380 and 900 nanometres, and radiations in the short wavelength infrared, i.e. having a wavelength comprised between 900 and 1700 nanometres.