Clause 10 Vertical sectors
Maritime Rules Part 22: Collision Prevention
(1) The vertical sectors of electric lights as fitted, with the exception of lights on sailing vessels underway, must ensure that—
(a) at least the required minimum intensity is maintained at all angles from 5 degrees above to 5 degrees below the horizontal; and
(b) at least 60 percent of the required minimum intensity is maintained from 7.5 degrees above to 7.5 degrees below the horizontal.
(2) In the case of sailing vessels underway, the vertical sectors of electric lights as fitted must ensure that—
(a) at least the required minimum intensity is maintained at all angles from 5 degrees above to 5 degrees below the horizontal; and
(b) at least 50 percent of the required minimum intensity is maintained from 25 degrees above to 25 degrees below the horizontal.
(3) In the case of non-electric lights these specifications must be met as closely as possible.