Yes, many buoys have lights, and the color and flash pattern tell you what kind of mark it is before you can see its shape. Red and green lights mark the sides of a channel. White lights belong to cardinal, isolated danger, and safe water marks (and in US waters also to mooring and information buoys). Yellow means a special mark, and blue and yellow alternating means a new wreck. Count the flashes, time the full cycle, and match it to the chart.
At night a buoy is just a light on a dark sea. You will not see the color of the hull or the shape of the topmark until you are close, often too close. What you can read from a long way off is the color of the light and its rhythm. This post is the night companion to what marine navigation buoys and buoy lights mean, which covers the marks themselves by day.
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| A lit red channel buoy at dusk off a harbour entrance. At night the color and rhythm of the light are what you read first. |
Do buoys have lights
Many do, not all. A lit buoy carries a small lantern on top, and the chart tells you its color and rhythm. An unlit buoy shows nothing at night. Some unlit marks carry reflective tape or panels that shine back when your spotlight hits them, which helps, but only once you already know roughly where to look.
The rules for buoy lights come from the IALA Maritime Buoyage System, which almost every lighthouse authority uses. The same logic applies in Region A (Europe, including Malta and the Med) and Region B (the Americas and parts of Asia). Only the red and green swap sides.
Start with the color
Color narrows it down fast. Here is what each one can mean.
| Light color | What it can be |
|---|---|
| Red or green | A lateral mark on the side of a channel, or a preferred channel mark where a channel splits |
| White | A cardinal mark, an isolated danger mark, or a safe water mark. In US waters also mooring buoys and information or regulatory marks |
| Yellow | A special mark, such as a cable, a pipeline, an exercise area, a fish farm, or a traffic scheme |
| Blue and yellow, alternating | An emergency wreck mark on a new danger |
Then count the rhythm
The rhythm is the pattern of light and dark. Charts and light lists write it in short codes. These are the ones you will meet on buoys.
- Fl means flashing. A short flash, then a longer dark period.
- LFl means long flashing. Each flash lasts at least 2 seconds.
- Fl(2) means a group of two flashes, then a pause. Fl(3) is three, and so on.
- Fl(2+1) means two flashes, a pause, one flash, a longer pause. This is the preferred channel light.
- Q means quick, 50 or 60 flashes a minute. VQ means very quick, 100 or 120 a minute.
- Iso means isophase. Light and dark last exactly the same time.
- Oc means occulting. The light is on longer than it is off, so it looks like it blinks off rather than on.
- Mo(A) means Morse code A. A short flash, then a long one.
- Al means alternating colors, for example blue then yellow.
How a buoy light reads on the chart
Next to the buoy symbol you will see a short line such as Fl(2) R 6s. Read it left to right. Group of two flashes, red, and the whole cycle repeats every 6 seconds. The period counts from the start of one group to the start of the next, so it includes the dark part.
A south cardinal might read Q(6)+LFl 15s. Six quick flashes, one long flash, and the pattern repeats every 15 seconds. If no color is written, the light is white.
Lighthouses often add a height and a range, for example 15m 10M. That is the height of the light and its nominal range in nautical miles. Buoy lights are low and small, so expect to see them much later than a lighthouse, and later still in a swell when the lantern drops behind the waves.
White lights on buoys
White is the color people ask about most. Under IALA, three kinds of mark use white, and each has a rhythm that cannot be confused with the others.
| Mark | White light rhythm | What it tells you |
|---|---|---|
| North cardinal | Q or VQ, continuous | Safe water lies to the north |
| East cardinal | Q(3) every 10s or VQ(3) every 5s | Safe water lies to the east |
| South cardinal | Q(6)+LFl every 15s or VQ(6)+LFl every 10s | Safe water lies to the south |
| West cardinal | Q(9) every 15s or VQ(9) every 10s | Safe water lies to the west |
| Isolated danger | Fl(2) | A small danger with water all around it. Give it room |
| Safe water | Iso, Oc, LFl every 10s, or Mo(A) | Navigable water all around, often a fairway or landfall buoy |
The cardinal flashes follow a clock face. East is 3, south is 6, west is 9, and north never stops. The long flash after the six on a south cardinal is there so that three or nine quick flashes cannot be mistaken for six when you lose count in a seaway.
In US waters the rules add a few white lights of their own. Safe water marks use Mo(A). Isolated danger marks use Fl(2). Mooring buoys and information or regulatory marks can also show white lights in various rhythms. Under US rules white lights have no lateral meaning, except on the Western Rivers, so a white light never tells you which side of a channel you are on.
Red and green lights
A red or green light marks the side of a channel. The color matches the mark. In Region A, coming in from sea, red is on your port side and green on your starboard side. In Region B it is the other way round, which is where "red right returning" comes from. Lateral marks can use almost any rhythm, often Fl, Fl(2), Fl(3), Q, Iso, or Oc. The one rhythm they do not use is Fl(2+1), because that is kept for preferred channel marks.
US rules say lateral lights are normally flashing or occulting, at no more than 30 flashes a minute. A quick flashing red or green light (60 a minute) can be used where the authority wants extra caution, for example at a sharp turn, a sudden narrowing, or a wreck.
If the red or green light shows Fl(2+1), you are at a preferred channel mark where the channel divides. The color is the color of the top band, and you treat it like an ordinary red or green mark if you are taking the main branch.
Yellow lights and special marks
A yellow light belongs to a special mark. It has no lateral meaning. It is telling you that something is there that you should look up on the chart, such as a cable or pipeline, a spoil ground, a military exercise area, a recreation zone, or a fish farm. Under IALA, special marks can use any rhythm that is not already taken by the white cardinal, isolated danger, or safe water lights, so yellow is never confused with white in poor visibility. In US waters a fixed or slow flashing yellow light is the preferred choice.
A blue and yellow light, or a flashing blue light
A light that alternates blue and yellow is an emergency wreck mark. Authorities lay it on a new wreck or a newly found danger until the danger is charted and marked with normal buoys. The buoy has blue and yellow vertical stripes and an upright yellow cross on top. The light shows 1 second of blue, half a second of dark, 1 second of yellow, half a second of dark, and repeats. If several are laid around one wreck, their lights flash in sync. Some also carry a radar beacon sending Morse D, or an AIS signal. Treat it as a fresh danger that may not be on your chart yet.
A plain flashing blue light on the water is usually not a buoy at all. In US inland waters, law enforcement vessels may show a flashing blue light while on duty. IALA chose the blue and yellow pattern for wreck marks so it would not be confused with those blue lights. Keep clear and listen on VHF.
Entering Grand Harbour in Malta at night
Coming into Grand Harbour, Malta's main harbour, at night, it is always the channel that defines the approach. The channel lights tell you where to go.
The entrance itself is marked by the two breakwater lights. The St Elmo breakwater carries a green light and the Ricasoli breakwater a red one, which is the Region A pattern for starboard and port coming in from sea. Check the current chart and light list for the exact characteristics before you go, because lights do get changed.
How to identify a buoy light at night
- Before dark, list the lit marks you expect to pass, with their color and rhythm from the chart.
- When a light appears, note the color first. Then time the full cycle with a watch, from the start of one group to the start of the next. Do it two or three times.
- Count the flashes in each group. Quick flashes are easy to miscount, which is why the south cardinal has the long flash.
- Match color, group, and period to the chart. If two lights could fit, wait for a second mark to confirm before you commit to a turn.
- Remember the lights can fail and buoys can drag. Check local notices to mariners, and cross-check with depth and your plotter.
Shore lights are the usual trap. A busy waterfront behind a channel can hide a small green flash completely. Slow down, look a little to one side of where you expect the light, and let your eyes adjust away from bright screens.
Buoy lights are only half of the night picture. The other half is reading position lights on sailing vessels, so you know which of those lights is a ship and which is a mark. Both sit on top of the basic navigational tools and techniques you use in daylight.
When you arrive and the lights lead you into a harbor, the next question is where to stop. That is covered in what berthing, docking, and mooring each mean. On a long passage, such as the ones in Atlantic passage timing, preparation, and safe routes, a landfall at night is where all of this comes together.
Count, time, match to the chart. Then trust what you have counted, not what you hoped to see.
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