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Just as a thought, I didn't know nanoparticulate sized SiO2 would block UV, but then again thinking about it, it's rather clever. Regular glass (a/k/a "flint glass" or regular window glass), which is mostly SiO2, blocks a lot of UVB and UVA. You have to put additives into the melt, I don't remember offhand; somebody in the Rare Earth series, or Rubidium, I forget, to make the glass they use in hospital solariums and such.

Regular glass DOES pass some UV through, of course, but a fraction vs. an open window.

But on the other other hand -- mercury vapor lamps, including the ones used for sunlamps, use a quartz tube (the high-pressure types used for face tanning and special medical applications, not the fluorescent-lamp low pressure phosphor coated tubes).

And quartz is nearly pure silicon dioxide. So is it just a matter of the intensity of the mercury vapor arc's UVA/UVB emission, that enough escapes along with the visible light? I guess even an 80% blocking would still let enough through; besides, those suckers wouldn't need the Watts they draw, I guess, unless serious attenuation was occuring. 500 - 700 Watts makes a lot of photons in the UVA/UVB range (no, I'm NOT going to do the calculations) in a mercury arc.

But anyway, back to the notion of an SiO2 based screen; there are so many people allergic to the agents in current use; SiO2 is chemically and biologically inert. (Unless you breathe in the dust.)

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