Week 18 - 4.29.12 - 5.5.12 - Fresnel
Materials: Copper, Sterling Silver, Convex Glass Lens
Pendant Dimensions: 1.69” H x 1.11” W x .375” D
In 1822 French engineer Augustine-Jean Fresnel introduced a revolutionary lens that dramatically improved lighthouse illumination.
Fresnel replaced multi-lamps and reflectors with a single lamp placed at the center, or focal plane, of the lens. The beehive-shaped lens had a central panel of magnifying glasses surrounded by concentric rings of prisms and mirrors. These were angled to gather light and direct it towards the focal plane where it was intensified and projected seaward. Fresnel’s lens was quickly adopted by the maritime world. Eventually, all the world's lighthouses were equipped with Fresnel’s lenses.
These lenses came in several sizes. The larger ones, referred to as ‘1st-Order’, were used at seacoast sites where they needed to be seen at the greatest distance. Most Great Lake sites used mid-size, or ‘3rd-Order’ lenses. An in-between size, called a ‘Third and a Half’ was also common at Great Lakes sites. Smaller, ‘5th-Order’ and ‘6th-Order’ lenses were used on piers, breakwaters, and along our rivers. Several firms in Paris were the only manufacturers making these lenses for many years, and thus most American lighthouses had/have French-made lenses.