= Lighthouse
{wiki}
A <lighthouse> produces a visible navigational light from a fixed coastal or offshore structure. Its optical system concentrates light into selected directions rather than radiating equal useful intensity everywhere. A <Fresnel lens> can approximate the focusing action of a thick lens through stepped sections with less material. Rotating or switched beams give characteristic flash patterns that distinguish stations. Visibility depends on intensity, atmospheric scattering and the geometric horizon, so greater source power alone does not remove every range limitation.
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