Seaman's Handbook

ANNEX I. Positioning and technical details of lights and shapes

(a) (i) In the forward direction, sidelights as fitted on the vessel shall show the minimum required intensities. The intensities shall decrease to reach practical cut-off between 1 degree and 3 degrees outside the prescribed sectors. (ii) For sternlights and masthead lights and at 22.5 degrees abaft the beam for sidelights, the minimum required intensities shall be maintained over the arc of the horizon up to 5 degrees within the limits of the sectors prescribed in Rule 21. From 5 degrees within the prescribed sectors the intensity may decrease by 50 per cent up to the prescribed limits; it shall decrease steadily to reach practical cut-off at not more than 5 degrees outside the prescribed sectors.(b) All-round lights shall be so located as not to be obscured by masts, top masts or structures within angular sectors of more than 6 degrees, except anchor light prescribed in Rule 30 which need not be placed at an impractical height above the hull.