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A Fresnel lens is a thin optical lens that has the properties of much thicker and heavier lenses. It consists of concentric rings of segmental lenses that bend and magnify light rays, creating a single, concentrated beam of light. This design allows the lens to capture more oblique light from a light source than conventional lenses, making its beam visible across greater distances. The light from the first Fresnel lens, placed in a lighthouse in 1823, could be seen from how far away? Discuss
Source: The Free Dictionary