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A light is a pattern, not just a tower.

Mariners read a lighthouse by its character: the colour, the grouping of the flashes, and the time the pattern takes to come round again. This site puts five published characters beside the authority’s own figures, and keeps historic numbers in view when they differ from today.

Watch a character How a light is read
A white lighthouse on a small island at night, with beams of light radiating across a starry sky, and low white buildings beside a path
Boston Light at night, 8 August 2016, in Boston Harbor. The Coast Guard caption records that the beams come from an 1859 Fresnel lens. Photograph by Petty Officer 3rd Class Andrew Barresi, U.S. Coast Guard, a work of the U.S. federal government and in the public domain.Photo: Petty Officer 3rd Class Andrew Barresi, U.S. Coast Guard · Public domain · Commons

What this site is for

It is a site about working aids to navigation. The published character is Fl (2) 10s, and the published range of the light is 17 nautical miles.⁠1 The same idea holds at Fastnet and at Hook Head, in the wording Irish Lights publishes today.

Trinity House describes the original tower, completed in 1698, as the first lighthouse to be built on a small rock in the open sea.⁠1 From candles and open fires to a stepped glass lens, the job has been the same: make a light that a mariner can tell from the next light along the coast.

  1. Trinity House, “Eddystone Lighthouse,” retrieved 15 November 2026