Fresnel lenses are a special kind of lens that is much lighter in weight than conventional lenses. This made them very suitable for use in lighthouses, where lens diameters could be as large as 3 meters.
Fresnel Lens Development
Fresnel lenses were developed by French physicist Augustin-Jean Fresnel. Fresnel’s work expanded upon the work done in 1748 by Georges de Buffon. De Buffon realized that a lens only needed one curved surface to effectively bend light. By cutting the glass away from the inside of the lens, he was able to create a lighter lens with less material.
Fresnel continued this work, by finding he could remove greater amounts of material by cutting glass from the lens surface leaving a pattern of a series of concentric rings. Modern Fresnel lenses are made not just from machining glass, but can also be made from plastic for use in car headlights.
Figure 1. A Fresnel lens (a) cross section compared to an equivalent plano convex lens
Fresnel Lens Quality
The optical quality of Fresnel lenses is relatively poor, but for applications where this is not a concern, their better focusing power to weight ratio makes them suitable for a number of tasks, most notably in lighthouses. The first commercial application of a Fresnel lens was in 1822 in a lighthouse, Cardovan Tower, on the Gironde River in France. This was followed by Fresnel lenses being installed in new lighthouses along the coast of Normandy and Brittany.
Modern Lens Applications
Modern manufacturing methods mean that Fresnel lenses can be simply stamped or molded from transparent plastic. Production of these lenses is very inexpensive and they can be found in everything from children’s toys and sheet magnifying glasses through to projection televisions and overhead projectors.
This article was updated on 11th March, 2019.