20Application (Lights)
1The rule in plain words
COLREG sets when lights and shapes are shown and requires extra lights not to confuse or hinder a proper look-out.
When do the light rules apply?
They apply from sunset to sunrise in all weathers.
What about daylight?
If carried, prescribed lights are also exhibited from sunrise to sunset in restricted visibility, and may be exhibited whenever necessary.
Can you add another light?
Only if it cannot be mistaken for a COLREG light, does not impair the visibility or distinctive character of prescribed lights, and does not interfere with a proper look-out.
What about shapes and the annex?
Rules concerning shapes are complied with by day; the lights and shapes specified must meet the specifications of Annex I to COLREG.
2Key points
- 1
All weathers · lights: sunset → sunrise.
- 2
Sunrise + restricted visibility → prescribed lights, if carried.
- 3
Other light: no mistaking · no impairment · no interference.
- 4
Shapes: by day · lights and shapes → Annex I specifications.
3Frequent mistakes
Wrong: "Bad weather suspends the light rules."
Right: The Rules apply in all weathers.
Wrong: "Prescribed lights are forbidden in daytime."
Right: If carried, they are also exhibited in restricted visibility by day.
Wrong: "Shapes follow the sunset-to-sunrise window."
Right: Rules concerning shapes are complied with by day.
4Exam keys & interpretation
Exam keys
- "Sunrise to sunset" needs the cue "restricted visibility"; do not treat daylight as a blanket rule.
- "If carried" qualifies prescribed lights in daytime; it is not a ban.
- Test an extra light against mistaken identity, visibility or distinctive character, and proper look-out.
How to read it
- Read "may be exhibited" as permission when necessary, not an automatic daylight requirement.
- Annex I supplies technical specifications; it does not replace compliance with the lights-and-shapes rules.
5Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
(a) Rules in this part shall be complied with in all weathers.
(b) The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out.
(c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.
(d) The Rules concerning shapes shall be complied with by day.
(e) The lights and shapes specified in these Rules shall comply with the provisions of Annex I to these Regulations.Source: U.S. Coast Guard — International Navigation Rules (2024)
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
My notes for this unit
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