Fired Up For Fresnel -> The Lens That Changed The World Of Light
I’m always awed by works that combine science and art, and the Fresnel Lens, the ~1-ton piece of multi-prismed glass which tops our lighthouse tower is one of these masterpieces. No single creation has changed the course of lighthouses (and even, our understanding of light itself) more than this amazing lens. In a time when the world believed light was composed of corpuscles (particles), an unassuming, timid and introverted Frenchman believed otherwise. His wave theories, and subsequently his invention of the Fresnel lens revolutionized the world. It’s a story I tell (in very abbreviated version) at the lighthouse & it’s one of the ones I want to pass on to you. Think I have a Fresnel fetish? You bet your fanny I do….
To understand the importance of this invention you have to go back several centuries in time. Prior to the mid-1700’s lighthouses were basically simple towers lit with open flames of either wood, coal fires or candles. Some improvement came about in 1780 with the development of a smokeless oil lamp (the “Argand” lamp) and parabolic reflectors, but the lights were still disappointingly feeble. Ships were either drawn dangerously close to the coast trying to find the weak lights, or never even saw them and shipwrecks were a constant & costly hazard. The problem was the parabolic reflectors wasted far too much of the light. Even the best of them lost at least 1/2 of their light on reflection and they just didn’t reach far enough out.
In 1819 Augustin-Jean Fresnel a slight and “artistically” constituted man was newly appointed to Napoleon’s Commission des Phares (Lighthouse Commission) in France. At this point he had already been working on the wave theory of light for many years and almost immediately realized the light problem could be solved by placing a lens in front of the light and refracting (bending) the light to capture it rather than reflecting it off a mirror in the back. The problem was that to be functional the lens would have to be placed really, really close to the light source and this, in turn, meant it had to be really, really thick, so thick as to be practically useless. More light would be lost going through the lens than even the old reflectors.
The resolution of this tricky problem was the key to everything.
Fresnel had the inspiration of breaking up the single curved surface into multiple, smaller prisms which would act like a giant lens when put together. He immediately started work on the concept and in 1821 was able to demonstrate his first success. By 1823 the world’s first Fresnel lens was installed at the Cordouan Lighthouse in southwestern France and the brilliance of the new light was astonishing. It took another ~25 years, an industrial revolution (basically the introduction of the steam engine) and the brother of Fresnel (who carried on his work after his death) to perfect Fresnel’s original vision, but the final lens was a masterpiece. By the mid 1800’s some version of the Fresnel lens was glowing at almost every lighthouse in Europe, parts of Africa, Asia and South America.
All except America…
In America thanks to a stingy, sourpuss (he looked it too) accountant by the name of Stephen Pleasanton the adoption of the new device was resisted until 1850 and even a bit further after that. A rather juicy story of internal politics, money & backhanded subterfuge delayed Pleasanton’s firing, but once he was gone the newly appointed Lighthouse Board went full force and by 1859 there was a Fresnel Lens in almost every lighthouse in America. Fresnel’s vision of light was complete.
There is SO much more to this story, including the importance that lighthouses (and the Fresnel lens) played in the Civil & World Wars, the stories of mercury baths (some lighthouse keepers literally went nuts), and how Fresnel lenses are still used today (in theater lighting, for example) and it’s all brilliantly written in the book “A Short Bright Flash“, which I highly recommend for all you aspiring and converted lighthouse nutters. Frikkin’ fascinating story!
But beyond the story are the original Fresnel lenses themselves. There are so few of them left, and even fewer in actual operation and even fewer that you can stand right next to. At Cape Blanco you get it all -> an operational, amazing Fresnel lens that you can stand within a foot of and get mesmerized by the moving rainbows writhing within her perfectly-formed prisms. Most people who come here are completely amazed once they get up close and can barely fathom the fact that a 1000 watt bulb only a few inches high can cast a light 26 miles to sea. That’s the beauty of the design, baby, as I so often tell them (or a little more formally anyway). On busy days I’ll try and give folks as much time as possible by the lens ‘coz I know how cool it it. On quiet days I’ll sometimes stand up there by myself & lose myself in her beauty, just because I can. It’s the lens that changed the world of light and if you ever get the chance, you’ve got to come see one.
Oh, yeah I definitely have a fetish 🙂
P.S. Believe it or not it’s been 9 years since Paul & I gave up the daily 9-5 grind in search of an alternative lifestyle. To mark the day, Paul’s updated his popular Recipe For A Happy Retirement post. This great little post combines our thoughts on what “retirement” means and what it takes financially, socially, mentally and physically to make the switch. Go have a read!SPONSORED LINK:
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