English: Section diagram showing how a
Fresnel lens (A) in a lighthouse works to collimate light from an oil lamp
(L) into a parallel beam. The Fresnel lens, invented in 1822 by Augustin-Jean Fresnel, increased the light projecting power of lighthouses greatly without the weight of a conventional lens of its size. Also shown are mirror strips
(m,n) mounted above and below the lens that most lighthouses had, to gather more of the lamp's light. Alterations: removed caption, erased blots in white areas, changed brightness levels to get rid of noise in white areas, sharpened light path lines.