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Old 13th Jun 2019, 11:49 am   #65
broadgage
Octode
 
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 1,392
Default Re: The lightbulb conspiracy

Filling a bulb with Krypton or Xenon instead of the cheaper Argon, can be used to either run the filament hotter and produce more light for the same energy, or alternatively the filament temperature and therefore the output can be left unaltered and the lamp life increased instead.

Vehicle manufacturers have chosen the second option of increased life in order to reduce warranty claims.

Krypton or Xenon filling is also popular for the better quality torch bulbs, generally to obtain more light from the limited and very expensive energy in batteries, rather than to extend the life.

There is no gain from gas filling very low current bulbs but it is worthwhile at higher operating currents.
Note that it is lamp current, not watts, that determines if gas filling is worthwhile.
A 12 volt 21 watt vehicle bulb will be gas filled but a 240 volt 25 watt bulb will usually be vacuum filled.

To determine if a working bulb is gas filled, or vacuum, light it and observe the temperature of the glass. A gas filled bulb will be hotter above the filament whereas a vacuum bulb will be equally hot above or below the filament.

A well used gas filled bulb will be blackened above the filament, a vacuum bulb more evenly blackened.

Vacuum bulbs are preferred for decorative use if exposed to the weather, being equally warm all over they withstand rain or snow better than gas filled bulbs with a hot spot over the filament.
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