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Re: [RFI] 120v halogen lights

To: rfi@contesting.com
Subject: Re: [RFI] 120v halogen lights
From: Martin Ewing <martin@aa6e.net>
Date: Tue, 06 Apr 2004 12:59:54 -0400
List-post: <mailto:rfi@contesting.com>
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

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


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

Stu Benner

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