The first order Fresnel lens for the Piedras Blancas Light Station was manufactured by Henri-Lapaute of Paris, France and was first shown on February 15, 1875. Augustine Fresnel was a French physicist who finally figured out how to produce a very bright light source for lighthouses in 1822 and he designed six sizes of lenses. His sixth order lenses were the smallest and have been used for such things as marking the entrances to harbors. First order lenses, the largest, were used in coastal lighthouses where visibility at the maximum range was required. More infirmation about Fresnel lenses can be found here.
The Piedras Blancas lens consisted of sixteen sides with eight flash, or bulls eye, panels occupying every other side. Each flash panel included a plano-convex lens in the center with dioptric and catadioptric prisms above and below it. Each flash panel concentrated the light falling on it from the inside into a circular beam so that eight beams of light emanated from the lens like spokes of a wheel. As the lens revolved, the beams went around and when one of the beams struck a ship at sea, an observer on that ship would see a brief but bright flash of light. The panels in between the flash panels contained horizontal prisms which focused the light into a very broad but less intense beam. Since the lens made one revolution every two minutes, the observer on a ship would see a bright flash every fifteen seconds and, in between the flashes, a fixed white light of lesser intensity. This characteristic is referred to as “fixed and flashing” or “fixed varied by flash”.
By 1916, the Lighthouse Board had determined that “fixed and flashing” lenses should be eliminated because, at great distances or when visibility was low, it was possible for a ship to see only the flashing portion of the characteristic and not the fixed portion. As every lighthouse had a different characteristic, this could cause confusion or misidentification of a lighthouse. So, in the spring of that year, the Piedras Blancas lens was reconfigured. The eight flash panels were grouped into four pairs and the panels between them were filled with opaque panels. At the same time, the speed of rotation was increased to one revolution per minute. As a result, a passing ship would now see two bright flashes close together every fifteen seconds and darkness the rest of the time.
In the center of the lens assembly was a light source consisting of a pool of lard oil with five concentric wicks in it. The fuel source was changed to mineral oil, or kerosene, in the 1890s and several configurations of burners were subsequently used. Rotation of the lens was enabled by a clockwork mechanism directly under the lens which was, in turn, driven by a drum with a 3/8 inch steel cable wound around it. The cable ran down the entire height of the tower and around a pulley fixed to the top of a weight and thence back up to the first landing on the stairway. When the mechanism was unwound, the weight resided in a well at the bottom of the tower. After the keeper wound up the mechanism, raising the weight all the way up to the first landing, gravity would drive the lens around for a few hours. Beginning in the1940s an electric motor was used to rotate the lens.
The rate of rotation was regulated by a centrifugal governor acting on feathering air vanes. Each night the rotation of the light was adjusted by measuring the time required for a mark on the large gear under the light to pass and return to a pointer mounted on a stand using a stopwatch. To slow the rotation, the vanes on the governor were adjusted to have more air resistance and, to speed up the mechanism, the vanes were adjusted to have less air resistance.
The light mechanism operated in this fashion for nearly 75 years until early 1949 when the lens, lantern room, ornate railing and the upper portion of the tower were removed by the U. S. Coast Guard. The Coast Guard judged that the tower could no longer safely support the lantern room due to an earthquake which had occurred on December 31, 1948. They placed a rotating aero beacon on top of the shortened tower. Before the Coast Guard was able to make a decision about what to do with the components from the site, four members of the Cambria Lions Club, Byron (Bing) Boisen, Eddie Shaug, Guy Bond and Roland Houtz, obtained permission to remove the lens and clockwork mechanism. Since the Coast Guard was unable to give or sell the lens to the Lions, they arranged to loan it to them and the lens was reassembled on a concrete pad at the Pinedorado Grounds on Main Street in Cambria’s west village.
After about forty years the lens and mechanism began to show damage from the elements since the lantern room had not been reconstructed around it. In 1990, Norman Francis, Jr., son of the last Lighthouse Service head keeper at Piedras Blancas, launched an effort to restore and protect the lens. The lens was cleaned and restored by the Coast Guard at their station in Monterey, California. Alex Lazrevich, a retired machinist, spent countless hours refurbishing the clockwork drive and other pieces in his garage. The Friends of Piedras Blancas Lighthouse, led by Bob Lane, constructed a new lantern room which has housed the lens and clockwork at the Pinedorado Grounds since 1996.