Navigation Lights Explained: Reading Vessels at Night

At night, a vessel becomes a pattern of coloured lights on a dark horizon, and those lights tell you almost everything you need to know: what type of vessel it is, which way it is pointing, and whether you are on a collision course. Learning to read navigation lights is one of the most rewarding parts of studying the COLREGs, because it turns a confusing scatter of dots into clear, actionable information. It is also one of the most heavily examined topics on European boating theory tests.

This guide explains the colours and positions of the standard lights, how they reveal a vessel’s heading and aspect, and the special light patterns that identify particular vessel types. Master the basics here and the more unusual combinations become much easier to decode.

The Three Core Colours and What They Mean

Navigation lights use just a few colours, each with a fixed meaning. Getting these firmly in your memory is the foundation for everything else.

• Red marks the port (left) side of a vessel. The port sidelight shines from dead ahead round to the port beam and a little behind it.
• Green marks the starboard (right) side. The starboard sidelight covers the same arc on the opposite side.
• White is used for the sternlight, seen from behind, and for masthead (steaming) lights, seen from ahead and the sides. White also appears in anchor lights and all-round lights.

A handy memory hook: “port” and “left” are both shorter words, and port wine is red. The green starboard light is on the right. Getting port and starboard the right way round is half the battle.

How Lights Reveal Heading and Aspect

Because each light shines over a defined arc, the combination you see tells you which way a vessel is facing relative to you. This is the concept of “aspect.”

If you see a red and a green light side by side with a white light above, the vessel is pointing more or less straight at you, showing you both bows. That is a head-on situation and demands attention. If you see only a green light (plus perhaps a masthead light), you are looking at the vessel’s starboard side, so it is crossing from your left to your right. See only a red light, and you are looking at its port side, crossing from your right to your left. A single white light with no colours usually means you are looking at the stern, so the vessel is heading away from you.

For a power-driven vessel, the masthead lights add another clue. A vessel over a certain length shows two white masthead lights, a lower one forward and a higher one aft. When those two whites line up vertically, the vessel is heading straight toward or away from you. When they are separated horizontally, you are seeing it side-on, and the direction of separation tells you which way it is travelling.

Standard Light Patterns by Vessel Type

Different vessels carry different combinations so you can identify them at night. The exact ranges and details are set out in the COLREGs, but the patterns to recognise are these.

A power-driven vessel underway shows a masthead (steaming) light forward, red and green sidelights, and a white sternlight. Larger vessels add a second, higher masthead light aft. A sailing vessel underway shows sidelights and a sternlight but no masthead steaming light, which is a key way to tell sail from power at night. Some sailing vessels may combine the sidelights and sternlight into a single tricolour lantern at the masthead.

A vessel at anchor shows an all-round white light, or two if it is a large vessel (one forward, one lower aft). A vessel not under command shows two all-round red lights in a vertical line and no steaming lights, because it cannot manoeuvre. A vessel restricted in her ability to manoeuvre typically shows red-white-red all-round lights in a vertical line. A vessel towing shows extra masthead lights and, depending on the length of the tow, a yellow towing light above the sternlight.

You do not need to recite every range for a recreational exam, but recognising these signature patterns is essential.

A Quick Way to Decode Any Light You See

When a light appears out of the dark, work through it in a fixed order and it will rarely defeat you.

• First, note the colours: any red or green tells you which side you are seeing; white alone often means a stern or an anchor light.
• Next, count the vertical lights: two or three all-round lights stacked up usually signal a special vessel like one not under command, restricted, or fishing.
• Then consider masthead lights: their presence means power-driven, their absence points to sail; their horizontal separation reveals aspect.
• Finally, put it together into a picture of type, heading and risk, and decide whether you are the give-way or stand-on vessel.

This disciplined sequence stops you jumping to conclusions and is exactly the habit examiners want to see.

Practising Until It Is Instant

Reading lights is a skill that rewards repetition. The colours never change, the patterns are finite, and once you have seen enough examples your brain recognises them automatically. In the boatingexamine course you can drill light-identification questions in exam format, including the awkward multi-light patterns, so that on a dark night or on exam day you interpret what you see in seconds.

FAQ

Which side is the red light on, port or starboard? Red is always on the port (left) side, and green is always on the starboard (right) side. A reliable memory aid is that “port” and “red” both go together with the shorter word “left.”

How can I tell a sailing boat from a motor boat at night? A power-driven vessel shows a white masthead steaming light in addition to its sidelights and sternlight. A sailing vessel shows no steaming light. So if you see sidelights but no white light shining forward from a mast, you are most likely looking at a vessel under sail.

What does a single all-round white light mean? On a small vessel it can be an anchor light, indicating the vessel is anchored. It may also be part of a small power-driven vessel’s lighting when combined with sidelights. Always look for accompanying colours and other lights before deciding.