Fresnel's Lighthouse Lenses
One of the rewards of walking up the scores of steps winding around the inside of the shaft of a lighthouse is turning inward and examining the glass optical system. This arrangement of prisms,lenses, and reflectors is used to project the light from a relatively small source in a beam that can be seen far at sea.
“Fresnel’s Lighthouse Lenses”, The Physics Teacher, 45, 550-551 (2007)
The Physics Teacher