I read that windows block majority of sun radiation, some even claimed that windows block almost 100% of UVB, but I found no reliable sources on windows blocking UVA. I guess it is due to the wavelength and UVA having longer wavelength means they penetrate deeper, but why is that so ?
Edit: I formulated my question poorly, instead I should’ve asked: what prevents us from creating windows that block UVA rays?
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Search for “soda lime glass transmission spectrum” and you get how typical window glass let through light depending on the frequency. The exact spectra will depend on the glass but all show that it go from 90% transparent to quite close to 0% transporter around 300 nm
[http://www.vidrasa.com/img/esp/trans_arglass.jpg](http://www.vidrasa.com/img/esp/trans_arglass.jpg)
UVA is defined as 315–400 nm so it will let a lot of light through for it and block practically all UVB,
The way question is because that is the color of soda lime glass. That is color in UV, visible, and IR light. You can see in the graphs that are starting to block IR light. It drops to semitransparent around 2500 nm and blocks all at 5000 nm.
An emerald is green because it lets green light through and absorbed another part of the visible spectra look at [https://www.geminterest.com/images/spectrabs/Vis-NIR/VNIR_EmeSyntHydroVertFoncRu.jpg](https://www.geminterest.com/images/spectrabs/Vis-NIR/VNIR_EmeSyntHydroVertFoncRu.jpg)the 500 nm peek and a lot trough up to 550 nm and that light we see as green.
When we usually talk about color we only care about it in the visible part of the spectrum but it is no different in UV and IR light. The difference is just you can see it but instruments can.
Another glass has other spectrums like borosilicate glass [https://www.continentaltrade.com.pl/files/MIKA/SZKLO/Szklo%20wodowskazowe%20i%20wzierne/Continental/Przepuszczalnosc%20szkla%20420_EN.png](https://www.continentaltrade.com.pl/files/MIKA/SZKLO/Szklo%20wodowskazowe%20i%20wzierne/Continental/Przepuszczalnosc%20szkla%20420_EN.png) that is common in cookware and uses in UV light bulb that is defined to emit UV light. It starts to block UV light at 200nm
So different glass that can look identically to you in visible light can behave quite different in UV and IR light
There is a complicated explanation for why that is the color of material by using how light interacts with atoms and molecules. It is out of the scope of this post and is a complicated explanation of why stuff has the color they have.
So the simple explanation is it lets through most UVA light because of the color of the commonly used soda glass in windows.
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