On Thursday, January 23, 2020 at 12:27:08 PM UTC-8, danny burstein wrote:

I was 99 percent sure I remembered those days of mercury arc
lamps needing that extra, outer, envelope 'cuz worries
about the UV intensity, and even that Duro Test had marketed
a "safety lamp" ("bulb") that, if the outer glass broke, would
shut itself down.

(this would have been the 1970's)

But none of the yung'uns around me believe that was ever teh case.

Any idea how they cleared up that problem?

Some mercury lamps have quartz envelopes, that take the high temperature, but
those ALSO pass UV. Most low-intensity lamps don't need quartz. and glass
that is opaque to UV is easily formulated. Welder's helmets always have such a
glass filter (in addition to the visible-light-attenuating dark ones).

Heck, some halogen incandescents need a safety glass pane, as well.