In article ,
"Grumps" writes:
Hello All

Does using a dimmer reduce the life of a halogen bulb (78mm 240V 100W
linear), or increase it?

Increase it, generally.

There's a theoretical possibility of reduction if the bulb wall
temperature drops below 250C (which stops the halogen cycle)
whilst the filament temperature is still high enough for
significant filament evaporation to occur, but I don't believe
this is the case with any current halogen lamp designs.

It was possible with the first halogen projector lamps which
didn't run the bulb wall as hot as today's halogens do (because
the pinch seals would fail at 350C, a lower temperature than is
the case today).

--
Andrew Gabriel
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