Fresnel lens

Fresnel lens

A Fresnel lens (left) compared with the solid lens (right) to which it is optically equivalent. By reproducing the curved surface of the solid lens as a series of rings separated by steps on a thin lens, the Fresnel lens effects a great saving in weight, allowing mechanically robust lenses of relatively short focal length to be fitted to searchlights, spotlights, and automobile headlights.

A Fresnel lens is an optical device for concentrating light that is made of concentric rings that are faced at different angles so that light falling on any ring is focused to the same point.