Every vehicle upon a highway within this state at any time from a half-hour after sunset to a half-hour before sunrise and at any time when it is raining in the driving zone and at any other time when there is not sufficient visibility to render clearly discernible persons and vehicles on the highway at a distance of 500 feet ahead shall display lights, including headlights, and illuminating devices as required in this part for different classes of vehicles, subject to exceptions with respect to parked vehicles as stated in this part.