Fresnel lens

A thin optical lens made of concentric stepped sections that focus or collimate light while using less material than a conventional lens.

Refraction: The change in direction of a wave as it passes between materials with different propagation speeds. Each groove redirects light through refraction, assembling rays at a focus.
Fresnel lighthouse lens: A large stepped glass lens system that concentrates a lighthouse lamp’s light into intense beams. Lighthouse optics were an early major use of Fresnel’s thin-section principle.
Augustin-Jean Fresnel: A French physicist whose work advanced wave optics and lighthouse lens technology. Fresnel developed the lens design that bears his name.
Convex lens: A lens thicker at its center than at its edges, which converges parallel rays of light. A Fresnel lens approximates a convex lens’s optical action with a thinner stepped profile.
Fresnel zone: A region of a wavefront whose contributions to an observation point have a characteristic phase relationship. Concentric zones explain how stepped optical regions can contribute toward one focus.
Overhead projector: A projection device that sends light through a transparent original onto a screen. A Fresnel lens gathers light from the projector lamp toward the projection optics.
French lighthouse system: The network of lighthouses maintained along France’s coastline to guide maritime navigation. The need to project lighthouse light farther helped drive adoption of Fresnel optics.
Aspheric lens: A lens whose surface profile is not part of a sphere or cylinder. Aspheric lenses retain continuous surfaces, unlike the discontinuous grooves of Fresnel designs.
Focal length: The distance from an optical system’s principal plane to its focus for parallel incoming rays. Groove geometry determines the distance at which the lens concentrates parallel light.
Solar concentrator: An optical device that directs sunlight onto a smaller receiver area. Large Fresnel lenses concentrate sunlight for thermal or photovoltaic systems.

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