DescriptionFresnel lens assemblies, Museum of Scottish Lighthouses - geograph.org.uk - 562670.jpg
English: Fresnel lens assemblies, Museum of Scottish Lighthouses Using paraffin lamps, one challenge in designing lighthouses was to collect as much as possible of the light into one narrow beam. The fresnel lens uses a set of glass prisms to deflect light leaving in all directions to be added to the horizontal beam. These elaborate lenses were expensive. More powerful electric lights only need a concave mirror, much cheaper.
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