Lost Fresnel lighthouse lenses are turning up around the country. Enthusiasts, travelers, and history buffs are hot on their trail.

When lighthouse enthusiast Kevin P. Duffus discovered a 12-foot-tall, 6,000-pound, bronze and crystal lens in a government warehouse he knew he solved a long-standing mystery. The whereabouts of the enormous missing Fresnel lens from the Cape Hatteras Lighthouse in North Carolina had long eluded preservationists and investigators, emerging as the “holy grail” of lenses. Today, the mammoth antique lens is on display at the Graveyard of the Atlantic Museum on Hatteras Island for locals and tourists to admire.

Modern day nautical “light navigation” may consist of a solar-charged battery on a steel pole, but it’s the romantic striped or white-washed conical structures from the nineteenth century that coastal travelers and lighthouse fans flock to, and that many organizations, including the United States Lighthouse Society, seek to preserve—especially ones containing the increasingly rare Fresnel lens. The problem is they're not easy to find.

When the U.S. Coast Guard started modernizing lighthouses in the 1940s, many antique Fresnel lenses were misplaced or lost track of because they have no identification numbers.

“They did not necessarily look at them as artifacts,” says Bob Trapani Jr., executive director of American Lighthouse Foundation. “They looked at the lenses as obsolete technology, yet their optic technique is still being applied today.”

The beehive-shaped handmade glass lenses were first created in 1822 by French physicist Augustine Fresnel, and quickly developed a reputation in Europe for being able to cast beams of light up to 20 miles away. Six types of these lenses were invented for different sized lighthouses, all with concentric rings of glass prisms with a magnifying glass shaped lens at the center. Most importantly, Fresnel lenses enabled lighthouses to develop their own unique beacon with distinct light characteristics for mariners.

While the movement to preserve the nation’s lighthouses took off in the 1980s, with the United States Coast Guard selling the buildings to private owners, it wasn’t until recently that the focus shifted from preserving the structures to finding and protecting the heart of the antique lighthouse—the Fresnel lens. For the past seven years, The United States Lighthouse Society along with the American Lighthouse Coordinating Committee has been compiling a list of their whereabouts.

Today, there are 500 known lenses, 80 of which are still in use throughout the United States, including in Sandy Hook Lighthouse in New Jersey, the oldest existing lighthouse in the United States. Most of these historic lighthouses are open to the public, and some even operate as coastal B&Bs.

Travelers curious about maritime history and seeing a Fresnel lens up-close can check into the working 1894 Heceta Head Lighthouse in Yachats, Oregon. On a cliff with sweeping views of the Pacific Ocean, it’s not only the brightest light on the Oregon Coast, but it’s also the most photographed lighthouse in the United States. Guests can stay in the Queen Anne–style Keeper’s House for $133 a night. And on the “other” coast in Bristol, Maine, the Pemaquid Point Lighthouse with 1856 Fresnel lens is available for weekly rentals for up to four people for $1,150.

Said to burn at “one million candlepower,” the first-order (largest) Fresnel lens at Jupiter Inlet Lighthouse in Florida inspired the lighthouse to found its own historical society, which conducts regular tours for visitors, who are allowed to climb the tower to see the lens and turquoise ocean views for themselves. (The sunset tour is especially popular.) And on Cana Island, Wisconsin, the local lighthouse, whose Fresnel lens is 139 years old, opened a special catwalk for glimpses of the artifact, and surrounding Lake Michigan, earlier this year.

For those who can bypass the buildings themselves and are interested only in lens lore and technology, the Maine Lighthouse Museum in Rockland has a diverse permanent collection of Fresnel lenses—the largest in the world.

Whether traveling near or far, The Lighthouse Society is appealing to the lighthouse lovers, and the public at large, for help in identifying any lenses not on the list in an ongoing effort to keep preservation of these historic artifacts alive.