On: Sunlight through glass does not provide Vitamin D

[Etheryte]

Quartz glass is transparent to the UV range, so it's not so much that we don't have the technology, it's just way more expensive than regular glass.

[masklinn → Etheryte]

Sapphire's also transparent down to far ultraviolet (150nm). Not sure about ALON.

[masklinn → masklinn]

Replying to self (because the edit window has gone): ALON apparently goes down to 200nm, so it's transparent to UVB (280-315)

[Florin_Andrei → masklinn]

Sapphire is an incredibly trivial compound, aluminum oxide.

The problem is, its melting point is huge. To make artificial sapphire you have to melt the stuff at very high temperature and let it drop and collect onto a ceramic base or something. And then you cut, grind and polish it into shape, which is not easy either because it's an extremely hard material.

The challenges to making a large flat plate of AlOx would be huge.