Fresnel lens, 1968.
© Science Museum / Science & Society Picture Library
This stepped lens is the type used in lighthouses. It was invented by French physicist Augustin Fresnel (1788-1827) in 1822 and because of its efficiency in capturing light, it was quickly adopted for use in lighthouses around the world. Its most common shape is that of a giant glass beehive around a central light. Shaped like a magnifying glass at its centre, with concentric rings of glass prisms above and below, the lens magnifies and concentrates the light into a powerful beam that can throw light 20 or more miles to the horizon.