RCW 46.37.270: Number of lamps required—Number of additional lamps permitted.

(1) At all times specified in RCW 46.37.020, at least two lighted lamps shall be displayed, one on each side at the front of every motor vehicle, except when such vehicle is parked subject to the regulations governing lights on parked vehicles.

(2) Whenever a motor vehicle equipped with head lamps as herein required is also equipped with any auxiliary lamps or a spot lamp or any other lamp on the front thereof projecting a beam of intensity greater than three hundred candlepower, not more than a total of two of any such additional lamps on the front of a vehicle shall be lighted at any one time when upon a highway.