Seaman's Handbook

PART C. Lights and Shapes : Visibility of lights

The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I to these Regulations so as to be visible at the following minimum ranges.(a) In vessels of 50 metres or more in length:
a masthead light, 6 miles;
a sidelight, 3 miles;
a sternlight, 3 miles;
a towing light, 3 miles;
a white, red, green or yellow all-round light, 3 miles.(b) In vessels of 12 metres or more in length but less than 50 metres in length:
a masthead light, 5 miles; except where the length of the vessel is less than 20 metres, 3 miles.
a sidelight, 2 miles;
a sternlight, 2 miles;
a towing light, 2 miles;
a white, red, green or yellow all-round light, 2 miles.(c) In vessels of less than 12 metres in length:
a masthead light, 2 miles;
a sidelight, 1 miles;
a sternlight, 2 miles;
a towing light, 2 miles;
a white, red, green or yellow all-round light, 2 miles.(d) In inconspicuous, partly submerged vessels or objects being towed: a masthead light, 3 miles.