Essential requirement:
Where navigation lights are fitted, they shall comply with the 1972 Colreg or CEVNI regulations, as appropriate.

Definition of lights:
Masthead light: Means a white light placed over the fore and aft centreline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel.

Sidelights: Means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees and so fixed as to show the light from the right ahead to 22.5 degrees abaft the beam on its respective side. In a vessel of less than 20 metres in length the sidelights may be combined in one lantern carried on the fore and aft centreline of the vessel.

Stern light: Means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135 degrees and so fixed as to show the light 67.5 degrees from right aft on each side of the vessel.

All-round light: Means a light showing an unbroken light over an arc of the horizon of 360 degrees.

Note 1) In a sailing vessel of less than 20 metres in length the lights prescribed in the table may be combined in one lantern carried at or near the top of the mast where it can best be seen.

Note 2) A sailing vessel underway may, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower green, but these lights shall not be exhibited in conjunction with the combined lantern permitted by note 1).