🚀 go-pugleaf

On Oct 4, 4:28 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net>
wrote:
> On 10/04/2012 02:57 PM, George Herold wrote:
>
>
>
>
>
> > On Oct 4, 12:43 pm, Jeff Liebermann<je...@cruzio.com>  wrote:
> >> On Thu, 04 Oct 2012 10:03:21 -0400, Phil Hobbs
>
> >> <pcdhSpamMeSensel...@electrooptical.net>  wrote:
> >>> On 10/03/2012 09:41 PM, Jeff Liebermann wrote:
> >>>> On Wed, 03 Oct 2012 10:32:57 -0400, Phil Hobbs
> >>>> <pcdhSpamMeSensel...@electrooptical.net>    wrote:
>
> >>>>> I don't know of any data that supports this common idea, but I'd be
> >>>>> interested in reading about it if anybody's actually done the experiment
> >>>>> carefully.
>
> >>>> It's an accelerated life test.  The deration curve of the incandescent
> >>>> light bulb is well known and assumed to be
> >>>>     (Vapplied/Vdesign)^-12 to ^-16 * Life at design voltage
> >>>> <http://www.welchallyn.com/documents/Lighting/OEM_Halogen_Lighting/MC3...>
> >>>> See Fig 5 on Pg 5 for the graph.  Nobody wants to wait 1000 hours for
> >>>> a bulb to blow.  So, they increase the applied voltage, which
> >>>> dramatically decreases the lifetime down to reasonable test times.
> >>>> Using a rack of bulbs, they obtain an average (or median) lifetime at
> >>>> the higher voltage.  Then, they work backwards on the curve to
> >>>> estimate what it would be at the design voltage.
>
> >>> You can't run an accelerated life test when the exponent isn't known
> >>> more accurately than 12 to 16.
>
> >> True, but I believe that's the range expected from different types of
> >> light bulbs (nitrogen filled, halogen, vaccuum), and not the range
> >> expected for a given device.  I suspect that more accurate exponent
> >> value could be empirically determined for a given device, and later
> >> used only for that device.
>
> >>>> 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.
>
> >> <http://en.wikipedia.org/wiki/Incandescent_light_bulb#Reducing_filamen...>
> >>     One of the problems of the standard electric light bulb is
> >>     evaporation of the filament. Small variations in resistivity
> >>     along the filament cause "hot spots" to form at points of
> >>     higher resistivity; a variation of diameter of only 1% will
> >>     cause a 25% reduction in service life. The hot spots evaporate
> >>     faster than the rest of the filament, increasing resistance
> >>     at that point a positive feedback that ends in the familiar
> >>     tiny gap in an otherwise healthy-looking filament.
>
> >> Note the photo of the filament with a break in the middle.  When I was
> >> quite young, I would break burnt out AC light bulbs to see what was
> >> inside.  If the filament was intact, the break was always somewhere
> >> near the middle.  If a piece broke off, one end of the broken piece
> >> was usually near the middle.  In later years, I would look at the
> >> remains of DC panel lights (usually type 47 for old Motorola radios)
> >> and noted that the breaks were always near the supporting terminals,
> >> probably due to metal migration.
>
> >>>>> I suspect that the notion that cycling is hard on bulbs comes from the
> >>>>> way that the bulb often fails at turn-on, when the thinnest hot spot
> >>>>> vapourizes before the rest of the filament has a chance to come up to
> >>>>> temperature and reduce the inrush current.
>
> >>>> Yep.  See my comments on the relatively high failure rate on the
> >>>> 40watt theater marquee lamps due to cycling.  The same lamps in the
> >>>> lobby and foyer were not cycled and seemed to last forever.
>
> >>> I was actually disagreeing with you.  There are lots of possible reasons
> >>> for the marquee lights failing prematurely.  I'm not a tungsten expert
> >>> myself, so I'd be very interested in seeing actual data that shows a
> >>> dramatic shortening of life due to cycling.  I'm not saying it's
> >>> impossible, just that I haven't seen any such data.
>
> >> So much for my anecdotal data.  My theater marquee experience was in
> >> about 1966.  The theater actually did keep records so that they could
> >> stock enough replacement bulbs, but I don't have copies of any of
> >> that.
>
> >> I tried Googling for similar repetative on-off tests and didn't find
> >> anything.  If I have time, I'll try again.  I must admit that the lack
> >> of test data does look suspicious.  Perhaps sending the idea to
> >> Mythbusters and have them runs a test?
>
> >>> The filament isn't tungsten-plated, it's pure tungsten or a low alloy.
> >>> The brightness drop comes from tungsten condensing on the envelope.
>
> >> Oops.  I thought it was plated.
>
> >>> And the connecting wire isn't plain steel, it's generally Dumet,
> >>>http://www.jlcelectromet.com/dumetwire.htm
>
> >>> which is a 42% Ni steel with OFHC copper or nickel plating.
>
> >>> You're making a lot of that up.  I'd still like to see
> >>> carefully-collected data.
>
> >> No, not fabricated.  It's my reliance on my memory in an area that I'm
> >> not familiar with.  I tried Googling for the wire used, couldn't find
> >> much, and made a bad guess.  The plating came from somehow getting
> >> thorium coated tungsten wire used in vacuum tubes mixed up with light
> >> bulbs.  Sorry for the errors and muddle.
>
> >>> Cheers
> >>> Phil Hobbs
>
> >> --
> >> Jeff Liebermann     je...@cruzio.com
> >> 150 Felker St #D    http://www.LearnByDestroying.com
> >> Santa Cruz CA 95060http://802.11junk.com
> >> Skype: JeffLiebermann     AE6KS    831-336-2558- Hide quoted text -
>
> >> - Show quoted text -
>
> > Hi Jeff, Phil.   First I know nothing about incandescent bulbs.
> > But how about this as a model of why turning bulbs on and off might
> > cause them to fail sooner.
>
> > 1.) I think we all observe that bulbs tend to blow when you turn them
> > on.
> > (unless you knock the lamp over or something.)
>
> > 2.) I assume that the failure is mostly due to the thinner �hot spots�
> > on the filament.   Thinner regions heat up faster (higher resistance
> > with equal current).
>
> > 3.) Now even if the thinner region doesn�t blow, it still gets hotter
> > and loses a bit more tungsten than the rest of the filament.   (For
> > that small amount of time that it�s turning on.)  But still this means
> > that turning on the bulb causes the thin region to become a bit
> > thinner.
>
> > And that�s it.  Repeated on and off means that the thin region has a
> > higher average temperature than the thick part of the filament.  It
> > evaporates faster and fails sooner.
>
> > George H.
>
> If the effect is real, that sounds like a good candidate for a
> mechanism.   Certainly you'd expect that to be important right near the
> end of the bulb's life, so maybe it's important throughout.
>
> Cheers
>
> Phil Hobbs
>
> --
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
>
> 160 North State Road #203
> Briarcliff Manor NY 10510
>
> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>
> - Show quoted text -

Yeah,  I was thinking about this while splitting/stacking wood
tonight.
If the time to fail goes as some big power of the voltage
(temperature),
then during turn on, small diameter variations (or defects)
get amplfied.

A 'long life' 40 Watt bulb would fail almost as fast as a 100 W'er.

(Of course I've got my 'lifetime supply' of 100W bulbs, and didn't
budget any for research.)

George H.