In modern lighthouses there are three kinds of lighting systems: the catoptric system, in which rays of light are reflected from silvered mirrors to form a parallel beam visible at a distance; the dioptric, or refractive, system, in which the rays pass through optical glass and are refracted as they enter and emerge from it; and the catadioptric system, in which rays are both refracted and reflected. Increased use of radio beams and radar has made the conventional lighthouse obsolete.
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