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Lighthouse lantern. The optical system of a lighthouse, known as the stepped Fresnel lens. It was designed by the French physicist Augustine Jean Fresnel in 1811. It generates the characteristic parallel beam of light from a lighthouse. Lighthouses are used to warn ships of dangerous stretches of coastline. The light from the bulb is focused into a beam which sweeps around in an arc. Each lighthouse has a unique light pattern enabling it to be identified. A man is standing next to the system to give the viewer an idea of scale.
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