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Speaker 1: Welcome to Brainstuff from half stuff works dot com, where

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Speaker 1: smart happens him Marshall Brain with today's question, is there

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Speaker 1: a way to make my sunglasses scratch resistant? Reflective sunglasses

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Speaker 1: often have a mirrored look. The lenses in these sunglasses

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Speaker 1: have a reflective coating applied in a very thin, sparse layer,

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Speaker 1: so thin that it's called a half silvered surface. The

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Speaker 1: name half silvered comes from the fact that at the

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Speaker 1: molecular level there are reflective molecules speckled over the glass

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Speaker 1: in an even film, but only about half of the

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Speaker 1: glass is actually covered by these speckles. The half silvered

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Speaker 1: surface will reflect about half the light that strikes it,

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Speaker 1: letting the other half go straight through. Often the mirror

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Speaker 1: coating is applied as a gradient gradually changes shades from

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Speaker 1: top to bottom. This provides additional protection from light coming

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Speaker 1: in from above, while allowing more light to come in

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Speaker 1: from below or straight ahead. This means that if you're driving,

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Speaker 1: the sun's rays are blocked, but you can still see

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Speaker 1: the dashboard. Sometimes the coating is bigradient. It's shaded at

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Speaker 1: the top and the bottom, but it's clear in the

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Speaker 1: middle of a lens. The big problem with these half

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Speaker 1: silvered sunglasses is that the coating is really easy to scratch,

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Speaker 1: while the glass itself is naturally scratch resistant. The coatings

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Speaker 1: apply to the glass as well as the most plastic

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Speaker 1: lenses are not scratch resistant. To compensate for this, manufacturers

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Speaker 1: have developed a variety of ways to apply optically clear,

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Speaker 1: very hard films to lenses. These films are made of

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Speaker 1: materials such as diamond, light carbon, and polycrystalline diamond. Through

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Speaker 1: a process of ionization, a thin, but extremely strong film

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Speaker 1: is created on the surface of the lens. This scratch

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Speaker 1: resistant coading works well in most cases. For example, you

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Speaker 1: can buy plastic lenses that are incredibly hard to scratch

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Speaker 1: because of these codings. But manufacturers have not been able

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Speaker 1: to successfully apply a scratch resistant layer on top of

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Speaker 1: the reflective coating used in mirrored sunglasses. Therefore, the scratch

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Speaker 1: resistant coding is applied first to protect the lens, and

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Speaker 1: then the reflective coding is applied over it. What this

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Speaker 1: means is that you have to take special care of

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Speaker 1: your reflective sunglasses or they get scratched really easily. For

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Speaker 1: more on this and thousands of other topics, Does that

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