In article , DoN. Nichols says...

Perhaps, though I still suspect UV penetration, even if somewhat
attenuated by absorption in the (quite thin) glass walls.

Even a very thin layer of the glass of the type used for
lamp envelopes will completely cut off any 254 nm radiation.

But the glass never sees this, it's all absorbed completely
by the phosphor. IOW if you could 'see' in the 254 nn UV
region, a smear of, say, cool-white phosphor on even a quartz
(suprasil) plate would still look like flat black paint.
Even though the quartz would allow UV to pass, even a very
thin layer of phospor absorbs the UV completely.

Phospors are quantum mechanical machines that gobble up
UV photons, and spit out visible ones. If they allowed
the higher energy photons to pass through, they would not
make good lighting equipment. :^)

Jim


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