A Fresnel lens is a type of lens developed by French physicist Augustin-Jean Fresnel for lighthouses.
The design enables the construction of lenses of large aperture and short focal length without the weight and volume of material that would be required in conventional lens design.
Compared to earlier lenses, the Fresnel lens is much thinner, thus passing more light and allowing lighthouses to be visible over much longer distances.
Source: Wikipedia

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