[RFI] Haolgens AND . . .

Stu Benner w3stu at myactv.net
Tue Nov 21 20:16:23 EST 2006

The reduction in life of an incandescent lamp when operated on DC versus AC
is attributable electromigration, a phenomenon in lamps commonly called "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

-----Original Message-----
From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
Behalf Of Donald Chester
Sent: Tuesday, November 21, 2006 3:07 PM
To: rfi at contesting.com
Subject: Re: [RFI] Haolgens AND . . .

>I was using my shack's 13 volt dc line, but I've found when
>I ran the bulbs from the dc supply the life was shorter.

I have experienced the same thing with conventional incandescent pilot 
lamps.  Running them on DC seems to lead to a very short life.

Someone once explained the reason, but I forget why.  It is some kind of 
"effect" with a proper name attached, and I recall it having something to do

with the molecular structure of the filament forming segmented rings on the 
surface of the wire.  It's been so long since I read the document that I 
don't have a clue where to look to find it again.

Don k4kyv

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