A lens lantern is a small, self-contained lamp structure which may sometimes be used to serve as a lighthouse. Unlike a regular

Fresnel lens A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the c ...

, the lantern requires no housing to protect it from the weather; its glass sides would

refract In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

and magnify the light in the same fashion as would the lens. Lens lanterns were popular alternatives to lighthouses in the nineteenth century; they required less care, were cheaper to erect, and could be fairly easily placed.

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