2 min read · Updated 28 June 2026
Navigation lights let vessels see each other and judge their heading at night. The system is simple and universal — red for port, green for starboard, white for the stern — and reading it correctly is essential for avoiding collisions in the dark. For sailors, one detail matters most: a sailing boat shows no steaming light, which is how you tell it from a power boat.
The core lights
Shown between sunset and sunrise (and in restricted visibility):
- Red sidelight — on the port (left) side.
- Green sidelight — on the starboard (right) side.
- White sternlight — facing aft.
- White masthead "steaming" light — shown by power-driven vessels.
The classic memory aid: there's "no red port left" — port, red and left all go together.
Reading a heading
The sidelights are arranged to shine from right ahead to just behind the beam on each side, with the sternlight covering the arc behind. Together they tell you which way a vessel is heading:
- See its red or green sidelight → you're ahead of its beam, it's heading somewhat towards you.
- See only its white sternlight → you're behind it, and overtaking.
This lets sailors judge the geometry of an encounter in the dark — vital for applying the right-of-way rules.
Sail vs power
The key distinction is the masthead steaming light:
- A power-driven vessel underway shows a white masthead light as well as sidelights and sternlight.
- A sailing vessel under sail shows only sidelights and a sternlight — no steaming light.
So: coloured sidelights with a white light above = under power; sidelights and sternlight with no masthead steaming light = under sail. Note a sailing boat motoring counts as power-driven and must show the steaming light.
Sailing-boat options
A sailing vessel underway shows sidelights and a sternlight. Beyond that:
- Smaller sailing boats may combine the sidelights and sternlight into a single tricolour lantern at the masthead — very visible and efficient.
- A sailing vessel may optionally show an all-round red-over-green pair at the masthead.
- At anchor, a vessel shows an all-round white anchor light.
(Exact configurations depend on vessel length and type under the COLREGs — this is the essential picture.) Navigation lights, the buoyage and the rules of the road together keep vessels safe at night; for the vocabulary, see the sailing terms glossary.
Frequently asked questions
- What are navigation lights?
- Navigation lights are the coloured lights vessels must show between sunset and sunrise, and in restricted visibility, so that other vessels can see them and work out their heading and what type of vessel they are. The core lights are a red light on the port side, a green light on the starboard side, and a white sternlight, with power-driven vessels also showing a white masthead 'steaming' light. Reading them correctly is essential for avoiding collisions at night.
- Which side is red and which is green on a boat?
- Red is on the port (left) side and green is on the starboard (right) side. These sidelights each show from dead ahead to a defined angle behind the beam on their side, so another vessel sees red if your port side faces them and green if your starboard side does. A handy memory aid is that 'port' and 'left' are both short words, and there is 'no red port left' — port wine, red, left, all linked.
- How can you tell a sailing boat from a power boat at night?
- By the masthead steaming light. A power-driven vessel underway shows a white masthead light (or lights) as well as its sidelights and sternlight, while a sailing vessel under sail shows only its sidelights and sternlight — no steaming light. So if you see the coloured sidelights with a white light above them, it is under power; if you see just the sidelights and stern light with no masthead steaming light, it is under sail. A sailing boat motoring must show the steaming light, because it counts as power-driven.
- What lights does a sailing boat show at night?
- A sailing vessel underway shows red and green sidelights and a white sternlight, and no masthead steaming light. Smaller sailing boats are permitted to combine the sidelights and sternlight into a single tricolour lantern at the top of the mast, which is very visible and efficient. A sailing vessel may also optionally show an all-round red-over-green pair at the masthead. A vessel at anchor shows an all-round white anchor light instead.
- Why do the sidelights only show forward?
- The sidelights are arranged to shine from right ahead to just behind the beam on each side, and the sternlight covers the arc behind, so that the lights together tell an approaching vessel which way you are heading. If you can see a vessel's red or green sidelight, you are ahead of its beam and it is heading somewhat towards you; if you see only its white sternlight, you are behind it and overtaking. This lets sailors judge the geometry of an encounter in the dark.