They used to be used in public places, so there was no point
stealing the lamps to use at home. I heard the NY subway still
uses them, but I would have thought they were pretty obsolete
now. Don't recall seeing them in any lighting catalogues for
perhaps 25 years now.
55V is normally held to be the optimum for 100W lamp.
However, it doesn't drop away quickly as you move away
from 55V. There have been 84V lamps made which are
designed to run on half-wave rectified 120V US mains,
with the aim of getting higher efficiency than 120V
lamps. Unfortunately, designing lamps to run off 240V
is about as bad as it gets in this respect (on the
basis that no one uses even higher voltage filament
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