CA Veh Code Section 25102.5

(a)

A schoolbus may be equipped with lamps mounted so as to be visible from the sides of the bus which may be lighted, in addition to other required lights, when, and only when, atmospheric conditions such as fog, rain, snow, smoke, or dust, reduce the visibility of other vehicles to less than 500 feet.

(b)

The type and mounting requirements of such lamps shall be established by regulations adopted by the department. The regulations shall be adopted by January 1, 1980.