Section 67.05-1 - Arrangement of obstruction lights(a) Structures having a maximum horizontal dimension of 30 feet or less on any one side, or in diameter, shall be required to have one obstruction light visible for 360°.(b) Structures having a maximum horizontal dimension of over 30 feet, but not in excess of 50 feet, on any one side, or in diameter, shall be required to have two obstruction lights installed on diagonally opposite corners, 180° apart, or as prescribed by the District Commander, each light to have a 360° lens.(c) Structures having a horizontal dimension of over 50 feet on any one side, or in diameter, shall be required to have an obstruction light on each corner, or 90° apart in the case of circular structures, or as prescribed by the District Commander, each light to have a 360° lens.(d) Where the overall dimensions of a structure require the installation of two or more obstruction lights, the lights shall all be mounted on the same horizontal plane within the limitations of height specified in § 67.20-5 , § 67.25-5 , or § 67.30-5 , as applicable.(e) Lesser structures and piles, pile clusters or flare templates, etc., will not normally be required to be marked by obstruction lights, when they are located within 100 yards of a Class "A", "B" or "C" structure marked by established obstruction lights, but they shall be marked with red or white retro-reflective material, installed as prescribed by the District Commander.(f) All obstruction lights shall be installed in a manner which will permit at least one of them to be carried in sight of the mariner, regardless of the angle of approach, until the mariner is within 50 feet of the structure, visibility permitting.CGFR 58-17, 23 FR 3377, May 20, 1958, as amended by USCG-2001-10714, 69 FR 24983 , May 5, 2004