Fresnel Lenses: Illuminating the Seacoast
By Donna K. Keesling
From the earliest times, man attempted to light the shoreline so that seagoing vessels would have a safer passage. But it wasn’t until Augustin Fresnel invented his refractive lens, which became known as the Fresnel lens, that the light from lighthouses was bright enough and strong enough to adequately illuminate the seacoast.
The first known lighthouses, built in Egypt around 280 B.C., stood at the entrances to harbors and were lit with an open flame. In the 1690s, a glass lantern room was installed in the Eddystone Lighthouse in England. The candles in the lantern burned more securely and brightly than open fires of earlier lighthouses. Eventually oil lamps backed with mirrors for reflection provided more light to warn vessels at sea. In the late 1700s, lenses were first used in lighthouses in England. The lenses were considered failures because of the huge loss of light due to the thickness of the glass and its poor quality. In 1811, France established a committee to investigate ways to improve lighthouse illumination – Augustin Fresnel was a member of this committee.
Augustin-Jean Fresnel was born in 1788. He had little formal education in his early years but became interested in science and mathematics when he was enrolled in school at the age of twelve. When he was sixteen, Fresnel began his technical education at the Ecole polytechnique in Paris. He was particularly skilled in graphic arts and engineering drawing. He continued his studies at the world’s oldest school of civil engineering, Ecole national des ponts et chaussees (National School of Bridges and Highways). While working on a project to build a road connecting Spain and northern Italy, Fresnel began studying light, with a special interest in diffraction – the process by which a beam of light is spread out as a result of passing through a narrow aperture.
In 1818 Fresnel published his treatise titled Memoir on the Diffraction of Light. Fresnel submitted his full theory to the French Academy of Sciences, which had announced that its annual prize for 1819 would be given for the best work on diffraction. Fresnel was awarded the Grand Prize for his work.
In 1811, the Commission des Phares (Commission of Lighthouses) was established. Due to his interest in and paper about diffraction, Fresnel was later tapped by the commission to review improvements in lighthouse illumination. Fresnel realized that the problem with existing lighthouse lenses – that the mirrors used for reflection lost half their light – could be solved by using lenses instead of reflectors. Through the process of refraction, a lens “could take all the light emanating from the source and direct it into a beam.”
His design, known as a dioptric or refractive lens, used a bull’s eye lens surrounded by an array of small lenses and prisms. The lenses and prisms were arranged in a stair-step configuration that bent and focused the light out to sea. As a result of this configuration, the Fresnel lens used about eighty percent of the light from the lamp. The light shone further out to sea than existing lighthouse lenses and could be seen through dense layers of fog.
Fresnel’s lenses were originally designed in six sizes, known as orders. Additional orders were developed in the late 1800s. The largest of the original lenses, known as a first order lens, was designed for use in coastal lighthouses and could shine up to twenty-one miles. Smaller order lenses were meant for use in harbors and ports. Fifth and sixth order lenses, the smallest used in the United States, were used on bays and rivers.
The first Fresnel lens, installed in the Tour de Cordouan lighthouse on France’s Gironde River, became operational on July 25, 1823. In the United States, the first lighthouses to receive Fresnel lenses were the Navesink Twin Lights in New Jersey in 1841. By the 1860s, all lighthouses in the United States were equipped with Fresnel lenses.
Fresnel’s original design was for a revolving, first order lens. He also designed a fixed lens in 1824. The fixed lens produces a steady light all around, while the revolving design produces a flash. A unique flash pattern can be produced by varying the length of light and dark periods. A clock-type mechanism enables the lens to rotate around the lamp to produce the flash. A list or chart describing the flash pattern, or characteristic, of each light aided mariners in determining their location.
Satellite-based navigation and other modern navigational tools have made the lighthouse lenses mostly obsolete. However, there are still a number of Fresnel lenses in working lighthouses throughout the world. Some Fresnel lenses are part of museum collections, including a third order Fresnel lens from a lighthouse on Bolivar Point, near Galveston, Texas that is on display at the Smithsonian National Museum of American History. A first order Fresnel lens, installed on Thacher’s Island in 1861, is on display at the Cape Ann Museum in Gloucester, Massachusetts. This first order lens, weighing over a ton, is ten feet tall and six feet in diameter, and is comprised of 290 glass prisms set in a bronze frame.
Augustin-Jean Fresnel died of consumption (tuberculosis) on July 14, 1827, at Ville-d’Avray in France – a few short years after the first Fresnel lens was installed. Within one hundred years of its invention, 10,000 Fresnel lenses illuminated the coastlines throughout the world – ensuring safe passage for vessels at sea. To this day, his theories of light endure and form the basis of modern optics.
 Bruce Watson, “Science Makes a Better Lighthouse Lens,” Smithsonian Magazine, August 1999, https://www.smithsonianmag.com/science-nature/science-makes-a-better-lighthouse-lens-170677431/.
 Theresa Levitt, A Short Bright Flash: Augustin Fresnel and the Birth of the Modern Lighthouse (New York: W. W. Norton & Company, 2013), 29.
 “July 1816: Fresnel’s Evidence for the Wave Theory of Light,” American Physical Society News, July 2016, https://www.aps.org/publications/apsnews/201607/physicshistory.cfm.
 Levitt, 56.
 Martha Sessums, “Lighthouse Lore: French Fresnel Lens Brought Light to Naval Navigation,” France Today, September 24, 2021, https://francetoday.com/learn/apps-technology/lighthouse-lore-french-fresnel-lens-brought-light-to-naval-navigation/.
 “Fresnel Lens,” National Park Service, last updated September 16, 2019, https://www.nps.gov/articles/fresnel-lens.htm.