Chart № 3 · The language of lights
Reading the Lights
No two lighthouses on the same stretch of coast speak alike. Each has a rhythm, a colour and a period, printed on the chart in a shorthand that looks like code and is really a kind of poetry. Here is how to read it, and how to recognise a light in the dark with nothing but a stopwatch.
Anatomy of a light
On my old charts of the Wadden, beside the little magenta flare of each lighthouse, there was a line of text. Here is a typical one, broken into its parts:
Fl(3)W15s28m23M
| Part | Means |
|---|---|
Fl(3) | The character: flashing, in groups of three. |
W | The colour: white. (R red, G green, Y yellow; nothing written usually means white.) |
15s | The period: the whole pattern repeats every 15 seconds, measured from the start of one group to the start of the next. |
28m | Elevation: the height of the light above the reference water level, not the height of the tower. |
23M | Nominal range in nautical miles, in clear weather. Capital M is sea miles; small m is metres. |
The trick a navigator learns early is to count. You see a light ahead, you start a stopwatch on the first flash of a group, count the flashes, and stop on the first flash of the next group. Three flashes, fifteen seconds: you look at the chart, and there is only one light within range that says Fl(3) W 15s. Now you know where you are.
Your device asks for reduced motion, so the lamp waits for you to press Play.
Try it: watch a light keep time
Fl(2) W 10s
Group of 2 flashes, white, every 10 seconds.
0 sone full period10 s
The shorthand, letter by letter
These are the abbreviations you will meet on European and North American charts. Older charts and the lists of lights put full stops between the parts (Fl.(2)W.10s.); the meaning is the same.
| Abbrev. | Name | What you see |
|---|---|---|
F | Fixed | A steady, continuous light. Common on harbour piers; rare on major lighthouses because it is hard to tell from a ship or a house. |
Fl | Flashing | Short flashes, with darkness always longer than light. The classic lighthouse. |
Fl(2) | Group flashing | Flashes in groups, here pairs, then a long eclipse. |
LFl | Long flashing | A flash lasting two seconds or more. |
Oc | Occulting | The opposite of flashing: the light is mostly on and blinks off briefly. |
Iso | Isophase | Equal periods of light and dark. |
Q | Quick | 50 to 60 flashes per minute. |
VQ | Very quick | 100 to 120 flashes per minute. |
Mo(A) | Morse code | A letter in Morse, here A (dot-dash). |
Al | Alternating | Changes colour within the pattern, such as white then red. |
Dir | Directional | A narrow beam showing the line of a channel. |
Colours and sectors
Many lights are not the same colour in every direction. A sectored light shows white over the safe water and red or green over the dangers on either side. On the chart, the sectors are drawn as thin arcs radiating out from the lighthouse. Steering into a harbour at night, you keep the light white; the moment it turns red, you have drifted toward the rocks on one side, and if it turns green, toward the shoal on the other. It is the most elegant piece of navigation equipment ever devised, and it has no moving parts at all.
The clock face of the cardinal marks
Not every light is on a tower. The cardinal buoys that mark a danger tell you which side to pass with a white quick-flashing light, and the pattern is a clock face. North flashes continuously, like twelve o'clock. East flashes three times, like three o'clock. South flashes six times, plus one long flash so it cannot be mistaken for nine. West flashes nine times. Try Q(3) W 10s, Q(6)+LFl W 15s and Q(9) W 15s in the demo above, and the logic will stay with you for ever.
Fog signals: when the light is not enough
Fog is the oldest enemy of a lighthouse. A first-order lens can throw its light more than twenty nautical miles on a clear night and barely a cable's length in thick fog. So for most of their history, lighthouses also had voices.
The earliest were bells, rung by hand and later by clockwork, and guns fired at fixed intervals; some rock stations stored gunpowder by the barrel. Then came steam whistles, compressed-air sirens and, from the early twentieth century, the diaphone: a piston-driven horn that produced a deep, two-tone groan, starting high and ending with a sound like an enormous cow lowing at the end of the world. Canadian and Scottish coasts were famous for them. People who grew up near one can still imitate it, and often will, unprompted.
Like lights, fog signals had characteristics, so ships could tell one from another: Horn(2) 30s means two blasts every thirty seconds. Keepers dreaded fog for the work it made, since the engines had to be started and tended for as long as the fog lasted, sometimes for days. Today most of the great fog signals in Europe have been switched off, replaced by small electric emitters or simply by satellite navigation. A few are kept and sounded on special days, and it is worth travelling a long way to hear one.
Daymarks: how to recognise a lighthouse by daylight
A light is only half the identity of a lighthouse. In daytime the tower itself must be recognisable, so neighbouring towers are painted differently: bands, stripes, spirals, checks, or plain stone. These are a few of the patterns you will meet, with a lighthouse from the atlas that wears each one.
- Horizontal bandsHook Head, Ireland
- SpiralCape Hatteras, USA
- Solid colourLange Jaap, Netherlands
- Natural stonePhare d'Eckmühl, France
- Single bandLånge Jan, Sweden
- DiamondsCape Lookout, USA
Daymarks are not only paint. Shape counts too: a squat square tower like Kõpu, a slender cast-iron column like Lange Jaap and an octagonal brick shaft like Hel are all unmistakable from the sea, which is precisely the point. Next time you pass a lighthouse in daylight, ask yourself how you would describe it over a radio to someone who had never seen it. That is the question its builders were answering.