# Which Sunlight Components Can Pass Through Window Glass?

**URL:** <https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501>\
**Category:** Factual Questions\
**Created:** [February 16, 2004, 4:30pm UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501 "2004-02-16T16:30:49Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Surreal](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Surreal](https://boards.straightdope.com/u/Surreal)\
**Post date:** [February 16, 2004, 4:30pm UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501/1 "2004-02-16T16:30:49Z")

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Does ordinary window glass block out anything from sunlight, such as UVA/UVB rays?

Is it possible to absorb Vitamin D through glass? Is it possible to get a tan or a sunburn through glass??

Thanks.

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**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\
**Post date:** [February 16, 2004, 7:47pm UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501/2 "2004-02-16T19:47:40Z")

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Most glasses (and plastics) block light with wavelengths longer than 300 nm (3000 Angstroms). In fact, most of them cut off at even longer wavelengths – 330 to 350 nm. This will allow the longest wave UV rats through, but not the more dangerous short wave UV rays. You can still get a tan or a burn, but it takes a lot longer. I’m pretty sure that the wavelengths that allow the production of Vitamin D will pass through window glass (heck, it makes it through skin!).

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**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\
**Post date:** [February 16, 2004, 11:26pm UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501/3 "2004-02-16T23:26:28Z")

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> [@CalMeacham](#):
>
> Most glasses (and plastics) block light with wavelengths longer than 300 nm (3000 Angstroms). In fact, most of them cut off at even longer wavelengths – 330 to 350 nm. This will allow the longest wave UV rats through, but not the more dangerous short wave UV rays. You can still get a tan or a burn, but it takes a lot longer. I’m pretty sure that the wavelengths that allow the production of Vitamin D will pass through window glass (heck, it makes it through skin!).

i think its backwards, the shorter the wavelength the more dangerous it is so they probably cut off everything below 300nm. If they cut off everything above 300nm no visible light would get through.

According to this

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researchers found that “The optimum wavelengths for the production of [Previtamin D3] are between 295 and 300 nm, with an apparent maximum near 297 nm, results similar to those obtained in the rat and in organic solvents”. Simply, Provitamin D is ineffective at absorbing light above 315 nm for purposes of the light-catalyzed conversion to Previtamin D.

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [February 17, 2004, 12:23am UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501/4 "2004-02-17T00:23:36Z")

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Yes, Cal got it backwards. He was probably thinking frequency rather than wavelength. The low end cutoff for cheap glass is about 300nm.

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**Author:** ![Eleusis](https://avatars.discourse-cdn.com/v4/letter/e/f4b2a3/32.png) [@Eleusis](https://boards.straightdope.com/u/Eleusis)\
**Post date:** [February 17, 2004, 1:00am UTC](https://boards.straightdope.com/t/which-sunlight-components-can-pass-through-window-glass/229501/5 "2004-02-17T01:00:01Z")

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Cecil on [Can you tan through glass?](http://www.straightdope.com/classics/a1_163b.html)