Speaker 1: Welcome to brain Stuff from house stuff works dot com
Speaker 1: where smart happens. Hi. I'm Marshall Brain with today's question,
Speaker 1: how does a Frenelle lens work? If you've ever looked
Speaker 1: at the lens of a normal magnifying glass, you know
Speaker 1: that it's thick in the middle and it tapers down
Speaker 1: to next to nothing at the edges. In other words,
Speaker 1: it's shaped like a lentil, which is where the word
Speaker 1: lens comes from. It would not be very easy to
Speaker 1: make a giant magnifying glass lens because it would be thick, heavy,
Speaker 1: and hard to mount. The thin piece of plastic called
Speaker 1: a Fernell lens solve this problem. It's flat on one
Speaker 1: side and ridged on the other, and very thin across
Speaker 1: the whole surface. For Nell lenses were first used in
Speaker 1: the eighteen hundreds as the lens that focuses the beam
Speaker 1: and lighthouse lamps. Plastic for Nell lenses are used as
Speaker 1: magnifiers when a thin light lens is needed. The quality
Speaker 1: of the image isn't nearly as good as that from
Speaker 1: a continuous glass lens, but in lots of applications like
Speaker 1: a lighthouse, perfect image quality isn't necessary. The basic idea
Speaker 1: behind a for Nell lens is simple. Imagine taking a
Speaker 1: plastic magnifying glass lens and slicing it into a hundred
Speaker 1: concentric rings, like the rings of a tree. Each ring
Speaker 1: is slightly thinner than the next and focuses the light
Speaker 1: towards the center. Now take each ring, modify it so
Speaker 1: it's flat on one side, and make it the same
Speaker 1: thickness as the others to retain the rings ability to
Speaker 1: focus the light towards the center. The angle of each
Speaker 1: rings angled face will be different. Now, if you stack
Speaker 1: all the rings back together, you have a Fornell lens.
Speaker 1: You can make the lens extremely large if you like.
Speaker 1: Large for Nell lenses are often used as solar concentrators.
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