Application (Lights)
Rules concerning lights shall be complied with from sunset to sunrise and during restricted visibility.
Rule 20 establishes when lights and shapes must be displayed. The rules concerning lights apply from sunset to sunrise and, during those hours, no other lights shall be exhibited except lights that cannot be mistaken for the prescribed lights or that do not impair their visibility or distinctive character.
During restricted visibility and in any other circumstances when considered necessary, the prescribed lights shall also be shown. The prescribed day shapes are exhibited during daylight hours.
Recognition Sequence
Classify the vessel state first: underway, making way, stopped, at anchor, aground, towing, fishing, pilotage or special condition.
Read special lights vertically from top to bottom before using sidelights and sternlight to confirm aspect.
Then confirm the answer with the day shape, vessel length and any extra signal such as towing lights, deck illumination or a cylinder.
Exam Focus
Avoid identifying a vessel from one colour alone. Many mistakes come from spotting a red light and guessing before checking the full pattern.
If the question mentions 'making way', 'underway but stopped', 'at anchor' or 'aground', that wording usually determines which extra lights or shapes appear.
Key Takeaways
Navigation lights are mandatory from sunset to sunrise
The same lights are also required in restricted visibility by day or night
Extra lighting is only acceptable if it cannot be mistaken for the prescribed lights or degrade them
Day shapes matter in daylight even when the ship's lights are also relevant
Common Mistakes
Treating daytime fog as if navigation lights are optional
Using decorative or work lights that obscure or confuse the statutory lights
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