(a) Every vehicle upon a highway within this state:
(1) at any time from sunset to sunrise;
(2) at any time when it is raining, snowing, sleeting, or hailing; and
(3) at any other time when visibility is impaired by weather, smoke, fog or other conditions or there is not sufficient light to render clearly discernible persons and vehicles on the highway at a distance of 500 feet ahead;
shall display lighted headlamps, lighted taillamps, and illuminating devices, as hereinafter, respectively, required for different classes of vehicles, subject to exceptions with respect to parked vehicles and law enforcement vehicles, as hereinafter stated. In addition to the other requirements of this paragraph, every school bus transporting children upon a highway within this state, at any time from a half hour before sunrise to a half hour after sunset, shall display lighted headlamps, lighted taillamps, and illuminating devices as required by this paragraph, except that the operator shall use the lowermost distribution of light specified in section 169.60 unless conditions warrant otherwise.
(b) When requirement is hereinafter declared as to the distance from which certain lamps and devices shall render objects visible or within which such lamps or devices shall be visible, these provisions shall apply during the time stated in this section upon a straight level unlighted highway under normal atmospheric conditions unless a different time or condition is expressly stated and unless otherwise specified the location of lamps and devices shall refer to the center of such lamps or devices. Parking lamps shall not be used in lieu of headlamps to satisfy the requirements of this section.