How a light is drawn here
A characteristic tells you the rhythm, the colour and the period. It does not say how long each flash lasts or how long the gaps inside a group are. To draw a light, the site has to choose, and these are its choices.
The timings
| Rhythm | What the drawing assumes |
|---|---|
| Fl | A single flash lasts 12% of the period, kept between 0.3 and 1 second. In a group, each flash lasts 0.5 s with 1 s between flashes and 3 s between the parts of a composite group. |
| LFl | Each long flash lasts 2 s, the shortest a long flash may be. |
| Oc | A single eclipse lasts a quarter of the period, kept between 0.5 and 3 seconds. In a group, eclipses of 1 s with 1 s of light between them. |
| Iso | Half light, half dark. |
| Q, VQ, UQ | 60, 120 and 240 flashes a minute. Ultra quick is played slower, at 70% speed, so the screen never flashes more than three times a second. |
| IQ | Quick flashes for about three quarters of the period, then dark. |
| Mo | A dot of 0.5 s, a dash of 1.5 s, 0.5 s between them and 1.5 s between letters. |
When a group would not fit its period, everything inside it is shrunk in proportion. When a characteristic has no period, the drawing picks one and says so. Real lights vary: an old rotating lens sweeps its beam past you, so its flash swells and fades, while a modern LED switches on and off. These players draw the switch.
Official light lists often give the exact flash and eclipse lengths. When this site cites one for a real light, as for Cape Hatteras, the note under that light says so; the drawing itself still uses the defaults above.
Not for navigation
This is a place to learn the grammar. For the lights in your own waters, use the official list of lights and the current chart: characteristics change when a light is modernised, and a book or a website can fall behind.
Sources and licences
Definitions of the rhythm classes and the quick rates: Canadian Hydrographic Service, Chart 1, section P. Further rules of the notation: Light characteristic on Wikipedia. Each real light's characteristic, height and range come from that lighthouse's Wikipedia article, linked under it. Facts drawn from Wikipedia are restated in the site's own words; Wikipedia's text is available under CC BY-SA 4.0.
Type: Atkinson Hyperlegible Next and Atkinson Hyperlegible Mono, by the Braille Institute of America, under the SIL Open Font License 1.1. Atkinson was drawn to be easy to tell apart letter from letter, which matters when Fl, FI and F1 mean such different things.
Everything else, including the players and the pictures they draw, is made by the site.