[RFI] 120v halogen lights

[Martin Ewing]

Interesting, if OT.  The effect may be real, but I am trying see the 
physics.  The E-field seems too small to push W atoms around.  They are 
neutral.  But maybe there's a slight ionization.  Or momentum transfer 
from the electrons? Which end gets the "notch"? Hmm...

Whatever it is, lifetime should improve dramatically if you reduce the 
temperature -- run at reduced voltage, AC or DC.

Anyway, on the original topic -- old-fashioned iron-core transformers, 
variable transforms and/or rheostats (do we still use that word?) are 
the way to go.

73, Martin AA6E

Subject:
Re: [RFI] 120v halogen lights
From:
stuart benner <w3stu at myactv.net>
Date:
Mon, 5 Apr 2004 12:55:06 -0400

To:
rfi at contesting.com


The reduction in life of an incandescent lamp when operated on DC versus AC is
attributable to a phenomenon known as "DC notching." With DC applied, the
tungsten molecules migrate within the filament and the filament takes on a
"notched" appearance. The increased local resistance at the notch points along
with the reduced physical strength result in decreased life. If AC is applied to
the filament, this condition is avoided. A lamp operating on DC may have 20% to
50% of the same lamp operated on AC.

Much research was done on this at NASA-Goddard by their lamp expert Dr. Henning
Leidecker. One of the life-limiting factors on the earlier GOES spacecraft (and
others) was the life of the black bias (incandescent) lamp in the satellite
sensors.

Stu Benner
W3STU