Lighthouses had different techniques for rotating the light, most being too slow, making the light less visible. Augustin Fresnel proposed a mercury flotation system in 1825. Despite some lenses weighing over 6,000 lbs. the design reduced friction, increased rotation, and ultimately saved lives.

Lens Rotation by Thomas Tag

Introduction

There are three major types of lenses used in lighthouse towers – fixed, flashing, and a combination of fixed and flashing. Flashing lights are the most effective and powerful. The first lens created by Augustin Fresnel was a flashing lens. The flashing lens rotates and has a number of bull’s-eye lens panels that create beams of concentrated light (an eight-panel lens produces eight beams). As the lens rotates, the beams successively pass the view of the mariner giving what appears as a flash of light followed by darkness. Beneath the flashing Fresnel lens are several unusual mechanisms used to rotate and control the lens. The lens will be found to be supported on wheels, ball bearings, or on mercury contained in a large me… Continue Reading (9 minute read)