(a) The sidelights of vessels of 20 meters or more in length shall be fitted with matt black inboard screens and meet the requirements of § 84.15 . On vessels of less than 20 meters in length, the sidelights, if necessary to meet the requirements of § 84.15 , shall be fitted with matt black inboard screens. With a combined lantern, using a single vertical filament and a very narrow division between the green and red sections, external screens need not be fitted.(b) On power-driven vessels less than 12 meters in length constructed after July 31, 1983, the masthead light, or the all-round light described in Rule 23(d)(§ 83.23(d) of this chapter) shall be screened to prevent direct illumination of the vessel forward of the operator's position.