RE: Gas discharge lamps was Re: Blue Bulb Physics

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

Thanks for the lesson Professor!  I had heard this before, but when
thinking about it again this time I realized that this also explains
what I have observed on new vs old bulbs.  Just because the tungsten is
redeposited doesn't mean that it necessarily goes back to the same place
it was originally.  I've noticed that the filament on bulbs that have
been used for sometime is no longer a smooth coil of wire ... it looks
as though it has little chunks here and there.  

Steve Buchholz
San Jose, CA (USA)

> ----------
> back to W and I2.  The tungsten is deposited back on to the filament
> surface, thus replacing the tungsten which had vaporized at first.
> The I2
> is then free to go back and, so to speak, pick up another load of
> tungsten
> to deposit on the filament.  This total process tends to keep the
> tungsten
> where it belongs (part of the filament) rather than on glass surfaces,
> etc., and results in a significantly longer bulb life compared to an
> "ordinary" incandescent light without the halogen.  What's more, the
> scavenging effect of the halogen keeps the transparency of the
> envelope
> much better since nearly black metallic tungsten deposits are removed
> from
> the glass.
>