As normal bulbs the
halogen lamp has a
tungsten filament and
doesn't
contain air. This is because if it did, the
tungsten
filament would burn up
instantly. Therefore the
oxygen
is replaced with a mix of
nitrogen,
argon and
halogen.
To remove any
oxygen that might be left, the
filament is
often
layered with a
phosphor compound(called '
getter') that
reacts with
the
oxygen the
first time the bulb is used.
When the
current flows through the
halogen lamps
filament,
it
becomes white hot. At this
temperatures the
tungsten
starts to
vaporize. The
tungsten atoms that
flows away
from the
filament forms
volatile compounds with the
halogen.
These
compounds float around until they hit the
filament,
where the
heat breaks up the
compound, and the
tungsten melts
in to the
filament again. This
gives the
halogen lamp longer
a 'life'.
The
halogen lamp should not be
touched with bare
hands
since this
deposits salts and
fats on the
glass. This
is because the fat
burns and makes dark
spots on the glass.
The
salt fuses with the aluminosilicate glass of the bulb due
to the
high operating temperatures, and
weakens it's
integrity