WEBVTT - How does a Fresnel lens work?

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<v Speaker 1>Welcome to brain Stuff from house stuff works dot com

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<v Speaker 1>where smart happens. Hi. I'm Marshall Brain with today's question,

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<v Speaker 1>how does a Frenelle lens work? If you've ever looked

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<v Speaker 1>at the lens of a normal magnifying glass, you know

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<v Speaker 1>that it's thick in the middle and it tapers down

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<v Speaker 1>to next to nothing at the edges. In other words,

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<v Speaker 1>it's shaped like a lentil, which is where the word

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<v Speaker 1>lens comes from. It would not be very easy to

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<v Speaker 1>make a giant magnifying glass lens because it would be thick, heavy,

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<v Speaker 1>and hard to mount. The thin piece of plastic called

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<v Speaker 1>a Fernell lens solve this problem. It's flat on one

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<v Speaker 1>side and ridged on the other, and very thin across

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<v Speaker 1>the whole surface. For Nell lenses were first used in

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<v Speaker 1>the eighteen hundreds as the lens that focuses the beam

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<v Speaker 1>and lighthouse lamps. Plastic for Nell lenses are used as

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<v Speaker 1>magnifiers when a thin light lens is needed. The quality

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<v Speaker 1>of the image isn't nearly as good as that from

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<v Speaker 1>a continuous glass lens, but in lots of applications like

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<v Speaker 1>a lighthouse, perfect image quality isn't necessary. The basic idea

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<v Speaker 1>behind a for Nell lens is simple. Imagine taking a

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<v Speaker 1>plastic magnifying glass lens and slicing it into a hundred

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<v Speaker 1>concentric rings, like the rings of a tree. Each ring

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<v Speaker 1>is slightly thinner than the next and focuses the light

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<v Speaker 1>towards the center. Now take each ring, modify it so

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<v Speaker 1>it's flat on one side, and make it the same

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<v Speaker 1>thickness as the others to retain the rings ability to

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<v Speaker 1>focus the light towards the center. The angle of each

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<v Speaker 1>rings angled face will be different. Now, if you stack

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<v Speaker 1>all the rings back together, you have a Fornell lens.

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<v Speaker 1>You can make the lens extremely large if you like.

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<v Speaker 1>Large for Nell lenses are often used as solar concentrators.

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<v Speaker 1>For more on this and thousands of other topics. Because

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<v Speaker 1>house stof works dot com