The Lighthouse Lens

Vermilion’s lighthouse uses a single 100-watt-equivalent LED bulb, yet its light reaches 10 miles across Lake Erie because of lens technology developed in the 1800s by Augustin-Jean Fresnel. Earlier lighthouses used single or multiple whale-oil lamps, and only 3% of their light was visible to ships at sea. By the early 1800s, a curved reflector behind the light source improved efficiency and directed 39% of the light out to sea. In 1819, Fresnel designed a barrel-shaped array of lenses around the light source that reflected and refracted light into a single plane, allowing as much as 80% of the light to shine more than 20 miles out to sea. When the optic array was rotated and fitted with panels and colored glass, a lighthouse could flash in a distinctive pattern, helping mariners tell one lighthouse from another and pinpoint their location at night. Fresnel’s design was adopted worldwide, and although he originally created six sizes called orders, more were added over time. Vermilion’s lighthouse now has a reproduction Fifth Order Barbier & Fenestre Fresnel lens made of high-impact acrylic, with two hinged prismatic reflecting panels and optical sections containing 13 zones: 5 center dioptric, 5 upper catadioptric, and 3 lower catadioptric prisms. A volunteer lighthouse keeper maintains the structure and keeps the lens lit and clean.

Vermilion, Ohio · United States