Tuesday, September 19, 2017

Ocracoke's Fresnel Lens

Yesterday I wrote about Winslow Lewis' reflecting-illuminating lamps that were installed in the Ocracoke Lighthouse in 1823. These were used in spite of their inferiority to the Fresnel Lens which was invented in 1822 by French physicist Augustin Fresnel.

The Fresnel Lens was a technological leap in lighthouse lighting. With a precise arrangement of glass bull's-eyes and prisms the light was concentrated into parallel rays that produced a much brighter beam from a single light source.

1872 Diagram showing how a Fresnel Lens works



















In 1854 the Winslow Lamps in the Ocracoke Lighthouse were replaced with a fourth order Fresnel Lens.

Ocracoke's Fresnel Lens



















There are six orders of Fresnel Lenses, based on their size and focal length. First order lenses are the largest.

This month's Ocracoke Newsletter is a brief history of Howard's Pub. You can read it here: https://www.villagecraftsmen.com/news082117.htm.    

4 comments:

  1. A version of the Fresnel lens also replaced the mirror landing system that's a visual guide for pilots landing aboard aircraft carriers. A very versatile and valuable discovery!

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  2. Anonymous5:06 PM

    Have you heard anything about the coast guard station being opened up to the general public? pay for view as it were. That would be a wonderful idea. Put it back into the hands that are paying for it's upkeep -the public. We all know what would be the most popular place in the building - yes, the tower. Anyway it came up AGAIN on a local talk radio program here in Raleigh but I can never catch any of the details. There is not much bank for the buck spent on it now and a historical tourist attraction would be popular. How could it not?

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    Replies
    1. I have not heard of any plans to open the former Coast Guard Station to the public. Maybe someone else has information.

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  3. Fresnel Lenses in Lighthouses
    Inventor Augustin-Jean Fresnel was a French physicist and engineer who was the brains behind the Fresnel lens that was frequently used in lighthouses. He had produced up to six lenses that were targeted to be used in lighthouses. One of the more popular ones of these lenses is found in Hawaii, at the Makapuu Point Light. The Fresnel lens used there are the largest of the selection, with about 3.7m in height, and over a thousand prisms were used for these lenses. What has attracted many to use these lenses is because it has greatly reduced the material needed for light, as compared to more conventional lenses. This happens because instead of having one les, it is actually broken down into a set of concentric sections in the shape of a ring.

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