The Fresnel Lens: Our Shining Star
When you first encounter the Fresnel lens at the Cape May County Museum, your imagination may wander. If aliens visited, would they feel a kinship to this crystal ship?
The Fresnel Lens once lived inside the lantern room, located at the top of the third (yes, third) Cape May Lighthouse. This prism of light has reached across the heavens, guiding merchant and military ships safely into the Delaware Bay. Consider being met with a thick fog as it barrels in with no indication of where land meets the sea. Without this light, how many lost souls might there have been? The lighthouse sits on a spit of land that extends between the ocean and the bay, making a precarious route for sea-worthy vessels. The bay, a maritime doorway for overseas tankers and cargo ships destined to the ports of Philadelphia or Wilmington as well as for fishermen, continues to be a vital resource.
The Fresnel lens was lit for the first time on Halloween Eve in 1859. The revolving band of silver light glowed across the scatter of homes tucked amid Cape May Point’s brambles, woods, and barren beaches. Imagine that through the massive oaks and mulberry tree branches, with each rotation, distorted shadows entering attic windows.
In 1822, a French physicist, Augustin-Jean Fresnel, developed the lens, shaped like an immense glass beehive, and set into a bronze skeleton. After its construction, it was imported by ship with each section numbered in the appropriate order for reassembly. Then, it was reassembled in the lighthouse’s lantern room, with the final step placing the lamp in its center.
The Fresnel lens was quite a technological advancement. Its innovative design was and still is a work of art today. To understand that it was created over a hundred years ago and still cannot be replicated—even today with modern techniques—is absolutely astounding. It stands at 8’ 6” high and 6’ wide. There are 656 ground glass prisms set, using gypsum plaster, into 48 bronze frames. The prisms at the top and bottom were precision cut, refracting or reflecting the light at various points, resulting in a narrow sheet of light. Then the light was magnified at the center. All of that together created a concentrated beam with only 10% of the light lost. The lens rested on a revolving housing that turned using ball bearings, and was powered by a weighted clockwork system, similar to how a grandfather clock operates, with the keeper winding it each morning and evening. In addition, every Fresnel lens was constructed slightly differently based on its individual specifications, which makes this lens even more unique.
The Fresnel lens was used in a handful of lighthouses. Only when serious issues had been noted with other types of lights, the Lighthouse Board, appointed by Congress, approved hands-down that the Fresnel lens was far superior. They mandated that all new lighthouses or any that required updates were to install the Fresnel lens.
Over the years, with the various types of fuel and lamps used, the acrid fumes would burn the eyes and lungs of the keepers. This contributed, one suspects, to the keeper’s poor health, and was likely a contributing factor in hastening technological advances.
The land where the original Cape May lighthouse was located was purchased from John Stites in 1822, with the sole purpose to build a lighthouse. The first lighthouse was completed that same year and stood at the height of 88 feet, with over a dozen lamps with large reflectors acting as the light. The lighthouse stood for 24 years before being undermined by the sea—an ill-fated destiny, but predictable with a structure built on sandy soil.
In 1847, a second lighthouse was built further inland on higher ground, after earlier salvaging a significant portion of the first tower. The new tower stood at 78 feet. The lantern was quite small and poorly ventilated. The light, known as a catoptric light, used mirrors, over a dozen, and revolved once every three minutes as the beam flashed each minute.
Because of the poor construction of the lighthouse, a new one took its place and in 1857 the third and present lighthouse, standing at 157 feet, was built by the Army Corps of Engineers.
In 1859, the newly acquired First Order Henry-Leparte Fresnel Lens was assembled in the reconstructed tower’s lantern room. The lens cost approximately $15,000 at the time—which translates in 2022 to a whopping $519,600!
Originally, sperm whale oil was used in the lamp. As the light revolved each night it produced a white flash every 30 seconds with a range of 20 miles. A flash pattern is distinctive on every lighthouse, providing critical visual information about the identity of that lighthouse for those at sea. Because of the illumination output and magnification capability of the Fresnel lens, it became quickly obvious that the older lights couldn’t compare to this
Lamps in it evolved over the years. In 1878, the lamps consisted of three hydraulic lamps, each with five wicks, with a hydraulic float using oil. In 1885 a Funck eight-day lamp was installed. A round storage tank sat on top and held enough oil to last over a week, thereby eliminating a daily refill. In 1902, a large, pressurized kerosene mantle lamp was installed. It had five lamps, requiring 7-½ gallons of kerosene each night.
The light was electrified in 1933, still using the Fresnel lens. In 1936, an electric mechanized lamp and motor were installed with a rotating bulb holder. If one burned out, another bulb moved in its place. That same year a backup generator was employed and remained there until 1994, when it became no longer a requirement. It was located in the oil house—now the Oil House Museum gift shop located next to the present lighthouse.
The lighthouse keeper’s responsibility was to keep the lamp lit every night, ensure the crystal panels remained clean, and the next day remove any oily residue that may have built up during the previous night. Over the years, with the various types of fuel and lamps used, the acrid fumes would burn the eyes and lungs of the keepers. This contributed, one suspects, to the keeper’s poor health, and was likely a contributing factor in hastening technological advances.
The lamp was lit 30 minutes before dusk and extinguished 30 minutes after sunrise. The keepers operated in shifts, and during their watches they maintained the lamp and clockwork mechanism. During the day a keeper, wearing a linen overcoat to protect the crystal from any scratches, inspected the Fresnel Lens, trimmed the wicks, and checked on the level of oil in the lamp. In addition, he closed the curtains that lined the exterior windows, keeping at bay the damaging rays from the sun.
A lighthouse keeper’s job was not easy or without peril. It was labor intensive, requiring climbing the spiraling 199 steps each day with an additional 12 steps to reach the lantern, while weighted down with supplies. He had to remove snow and ice from the 16 exterior lantern windows. He’d check for bird strikes that may have damaged the windows, often standing on a ladder for a closer inspection—heaven forbid that he should be standing on the metal steps during a storm. In that case, the keeper had to quickly descend the lighthouse, exercising extreme caution. A bolt of lightning could strike the lighthouse and travel the metal steps acting as a conductor, killing him. I imagine him hightailing it down the steps, not taking a moment to stop on the brick landing and glance out the window to gauge the storm. Luckily, there aren’t any records of a Cape May Lighthouse keeper succumbing to such a fate.
In 1891, lightning struck the tower, snaking through an electric call bell’s wire that led to the keeper’s house, frying a few circuits, and damaging an interior wall according to local author, John Bailey, and the Lighthouse Board records. That was not the only time that lightning visited the tower. In the early 1900s, a keeper’s daughter experienced slightly burned skin, and became dazed from a glancing strike. In 2002, there was a significant lightning strike, but luckily no injuries. As an eyewitness account from an employee at the time, “At the first clap of thunder, all guests and staff were evacuated before a lightning bolt struck the towers.”
Lens front and side views.
Not only does a lone 14-plus story structure become a magnet for lightning, let us not forget that today, the lighthouse staff react just as quickly.
Thank goodness there weren’t any human casualties that day in 2002 but there had been one: the motor that turned the Aerobeacon (DCB-224) that began its life in 1946. The motor was damaged beyond repair, and replacement parts for it had become obsolete. What better lighting source than that relied on for aircraft, but a rotating airport beacon—Aerobeacon—named the DCB-224. The acronym DCB stands for Directional Code Beacon. It had a bullseye lens on each side and used a 1000-watt incandescent bulb. It was an amazing beacon. It served to protect our shores for over 50 years!
There are 656 ground glass prisms set, using gypsum plaster, into 48 bronze frames.
And, what became of the Fresnel lens that served for over eight decades? The factory that once produced the Fresnel lens had been destroyed during World War II. The lens could no longer be repaired.
All that remains of the beacon are the lamp assembly and bulb, now on display at the Cape May Lighthouse.
In 1946, the Coast Guard loaned the Fresnel Lens to the Cape May County Museum where it continues to reside. It is on display in a permanent secure structure, meeting all the protocols to house such a priceless artifact. A loaned artifact that technically remains the property of the United States of America.
In 2002, when lightning damaged the motor in the long-standing beacon, the replacement light rotated in the opposite direction. Although the older light sometimes proved to be a nuisance as it swept across Cape May Point’s homes, often directly into windows, the sweep of the new beacon beam caught the unsuspecting residents off guard with some fraught by the change. However, they quickly adapted, as they understood that change is inevitable.
In 2014, my family visited the Cape May Lighthouse. When we reached the top and entered the watch room, a guide, Dave Yeager, greeted us. He had been a fixture in the lighthouse for decades. He explained to my family, often focusing directly on my young granddaughter, of the history of the various lamps used over the years. He pointed to the steps that led to a cordoned off area higher in the tower and explained how it was once home to the Fresnel Lens. My granddaughter peered up the steps.
He continued with a story about the lens, using words that a three-year-old could understand. Mr. Yeager said that it was like a glass playhouse where she could sit inside and look through the crystal walls and see a rainbow of colors. Since the round glass house was no longer there, could she imagine standing inside? She nodded her head yes.
Then, he said that another light took its place and asked if she wanted to hold that bulb (DCB-224). She smiled brightly. He instructed her mother to hoist her daughter up onto a windowsill, as Mr. Yeager entrusted her with it.
She was not only elated but proud that she was chosen to hold this special bulb. After she returned it to him, he handed her a blue ticket—really an entry stub—which she proudly clutched in her tiny hand the entire time as she flew down the spiraling staircase with nervous grandparents trying their best to keep up with her.
Even if you aren’t a history buff, just witnessing the Fresnel lens’s beauty and its sheer size will stick with you long after your vacation. The same holds true if you’re a local. So, find the time to pop into the museum. Perhaps you’ll be as awestruck by this century-old wonder of Cape May County as I was.
In 2009, when I first moved to the Point and went into my attic, the beam of light would wash through my oak tree and glimmer across the floor. Although it happened for a brief moment, it felt comforting to know that I was a part of this unique community that lived with the grand watchman keeping guard on our shores. ■
If you are traveling from Cape May, allow some extra time to visit the Cape May County Museum, a 13-mile drive, to view the county’s shining star. It is located at 504 North Route 9, Cape May Court House, New Jersey, and listed on the National Register of Historic Places. (609) 465-3535 Hours of operation: seasonal, call first to confirm or visit cmcmuseum.org