On Oct 5, 2:51*pm, Jeff Liebermann wrote:
On Thu, 04 Oct 2012 10:03:21 -0400, Phil Hobbs

wrote:
Yep. *As I understand it (possible wrong), AC filaments break in the
middle, mostly from vibration flexing.

I don't think so, because there's no mechanism for that, as I said. *The
wire is fully annealed at all times, so there's no possibility of
progressive fatigue failure.

Oscillating filament light bulb:
http://www.youtube.com/watch?v=t_DwwNVA-7Q
Whether the earths magnetic field is strong enough to induce such
oscillations is questionable.

While digging for the apparently mythical lifetime test data on
incandescent light bulbs, I've found numerous theories on why
filaments fail.

Grin, the internet as a 'fire hose' of information. I went searching
for something that contained "Philips tech. rev." and found a
reference to the following article,

H. Horster, E. Kauer and W. Lechner — The Burn-out Mechanism of
Incandescent Lamps Philips Technical Review 32,155-164, 1971.

It was referenced in "Illuminating Engineering - Page 32 - Google
Books"

But nothing about turn on failure... sigh.

Here is a patent by some of the same guys at Philips... lots of stuff
about the filament getting hottest in the middle.

http://www.freepatentsonline.com/3868159.html
(Actually a decently written patent.)

George H.



Tungsten evaporation, causing hot spots, is the most
common. *One suggested that thermal cycling hardens the tungsten and
makes it brittle. *Another suggested that the inrush current causes a
mechanical shock if it hits at the 60Hz peak, instead of at the zero
crossing. *Yet another speculates that the temperature differential
between the hot filament, and the relatively cold mounting structure
may cause cracking.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

G