Lighting Technology, 2nd Edition

6

Luminaires

 

6.1 Optical design theory

The Fresnel and plano-convex lenses

In 1748 George Louis Leclerc de Buffon originated the idea of dividing a plano-convex lens into separate concentric rings in order to significantly reduce the weight. In 1820 the idea was adopted by Augustin Jean Fresnel (pronounced ‘Frenel’) to overcome a real problem in lighthouses. Before this date the only way of controlling the light distribution from a lighthouse was with mirrors.

Fresnel adapted de Buffon's idea to make a one piece moulding of the separate concentric rings which could be pressed in a mould of large diameter but maintaining a thin cross section to reduce its weight. In this way, very short focal length lenses could be produced which would normally ...