One of the Fresnel lenses was in this building and not mounted in the tower. The doors were open so we could get a close up look of the huge lense in action.
Twin Lights holds a prominent place in American maritime history as the first lighthouse to use the Fresnel lens. In 1841, two of these revolutionary lighthouse lenses were installed: a "first-order" fixed light in the South Tower and a "second-order" revolving light in the North Tower. Developed by French physicist Augustine Fresnel, they were far superior to any navigational lighting apparatus being used in the country at that time and are still "state of the art" today.


These 1841 lenses resembled glass beehives and consisted of a Fresnel Lense series of prisms that surrounded a central light source. They were classified into seven sizes called orders. Seacoast lights like Twin Lights usually received a first or second order lens. With the installation of these Fresnel lenses, Twin Lights became the best coastal light in 1898 an enormous electric-arc bivalve lens, measuring nine feet in diameter, replaced the South Tower beehive-type light. To illuminate this new lens, the Lighthouse Service built an electric generator house on site. It was one of the brightest navigational lights ever used in the United States. Its beacon was visible for 22 miles and, under certain conditions, could be seen reflecting in the night sky 70 miles away. The light was so bright that the North Tower was taken out of service. It was re-lit in 1962 when a smaller commemorative light was placed there.