In article ,
Victor Roberts writes:

Ordinary incandescent lamps are made from soda lime glass,
which has enough conductivity at 100C to maintain a low
frequency (DC or 60Hz) discharge in T12 fluorescent lamps
using electrodes on the outside of the bulb. The place
where the wires are sealed in an incandescent lamp (the
pinch seal) is made from lead glass, that has much lower
conductivity than soda lime glass. Vacuum tubes are usually
made from borosilicate glass (Pyrex(R)) that has even lower
conductivity than lead glass, and much lower than soda lime
glass.

Thanks, interesting.

However note that Pyrex(R) no longer implies any particular
glass type, and in particular, it's no longer borosilicate
glass in the US.

--
Andrew Gabriel
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