May 27, 2011
The Fresnel lens is the 1822 invention of French physicist Augustine Fresnel who invented a lens that would make his name commonplace along the seacoasts of Europe and North America. Most lenses were handmade and shipped unassembled from France. Others were made in England. Early lens designs resembled a giant glass beehive, with a light at the center. The lens could be as tall as twelve feet high with concentric rings of glass prisms above and below a center drum section to bend the light into a narrow beam. Later designs incorporated a bull’s eye design into the center of the lens shaped like a magnifying glass, so the concentrated beam was even more powerful. Tests showed that while an open flame lost nearly 97% of its light, and a flame with reflectors behind it still lost 83% of its light, the Fresnel lens was able to capture all but 17% of its light. Because of its amazing efficiency, a Fresnel lens could easily throw its light 20 or more miles to the horizon.
Definitely read on to learn how flash panels or bull’s eyes were used to distinguish one light from the next and to view the different orders of Fresnel lenses that were used on the Great Lakes and also see Wikipedia’s Fresnel lens entry.
If you’re out and about this weekend, take some time to stop in at a Michigan museum!