OT?: Lightbulb life, curiousity

My electrical experience is being a journeyman electrician since '75.
Rich Grise writes:

*So, yeah, it should be clear that turning on a cold bulb is "harder on
it" than running the bulb continuously. But, as has been mentioned,
putting a number onto that tradeoff is something for the math theorists
or maybe rec.puzzles crowd. ;-)*

I once saw a film of a coiled filament turned on from a cold start.
Due to the large current allowed by the low resistance of the cold
filament,
the self inductance of the coil caused a large flexion of the coil for
a few cycles
until it heated up and the current dropped. I have noticed that
incandescent
bulbs often blow directly upon starting, and may be weakened due to hot
spots
and tungsten evaporation, and broken by this flexing
Possible, anyway. I am sure that many research papers have been done on
this,
but I enjoy puzzling over it myself, as I am sure that others do.
Edison was an
empirical inventor and investigator, as were many others. Good company.

tesseract
 
I Googled "causes of filament failure in incandescent light bulbs." Two
results:

http://www.eng-tips.com (search filament failure)

http://www.newton.dep.anl.gov/askasci/eng99/eng99244.htm

give some light on the subject.

tesseract
 
tesseract wrote:
My electrical experience is being a journeyman electrician since '75.
Rich Grise writes:

*So, yeah, it should be clear that turning on a cold bulb is "harder on
it" than running the bulb continuously. But, as has been mentioned,
putting a number onto that tradeoff is something for the math theorists
or maybe rec.puzzles crowd. ;-)*

I once saw a film of a coiled filament turned on from a cold start.
Due to the large current allowed by the low resistance of the cold
filament,
the self inductance of the coil caused a large flexion of the coil for
a few cycles
until it heated up and the current dropped. I have noticed that
incandescent
bulbs often blow directly upon starting, and may be weakened due to hot
spots
and tungsten evaporation, and broken by this flexing
Possible, anyway. I am sure that many research papers have been done on
this,
but I enjoy puzzling over it myself, as I am sure that others do.
Edison was an
empirical inventor and investigator, as were many others. Good company.

tesseract
Click to expand...

Early mainframe computers had hundreds or even thousands of small
incandescent lamps on the control panel. They used a DC voltage and a
diode in a "Keep alive" circuit that kept the lamps warm, but not enough
to give visible light in a normally light room. It extended the life of
the lamps quit a bit.

--
Former professional electron wrangler.

Michael A. Terrell
Central Florida
 
"w_tom" <w_tom1@hotmail.com> wrote in message
news:4298F92B.BA101869@hotmail.com...
....
No science fact says power cycling is destructive, as
claimed.
Click to expand...
Odd. I thought a filament turn on cycle included a nasty inrush surge,
followed by rapid heating, heat shock to the glass elements, high current
stress to any narrow spots or areas where heat flow is restricted by element
positioning, etc. That's why most failures we observe (in the mostly
intermittent operations we see in our homes) occur during the turn on
transition, not during steady state operation.
 
"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in message
news:3Nvme.62.
....
The only other observation I can add here is that I've had
the experience many times of turning on an incandescant
light and getting an immediate bluish flash, then dark, but
do not recall any lights burning out while on, either in my
presence or as indicated by a switch still on when the
light is burned out. I've always attributed this to turn-on
stress being harder on incandescant lights than hours on.
I cannot quite deny the contention that turn-on breaks
lights with only a few hours left anyway, but if that were
so, I would expect to have seen more lights fail while on.
Click to expand...
It is possible that operation life causes the majority of the growth of
inhomogenities, which then cause failure during the turn on transient. That
would, I think, be more or less consistent with our observations.


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From: Bela P. Havasreti <bph0872@bcstec.ca.boeing.com>
Subject: Re: Gasahol Update
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Date: Tue, 31 May 2005 16:59:32 GMT

On Mon, 30 May 2005 12:15:02 -0700, "RST Engineering"
<jim@rstengineering.com> wrote:

Wholesale avgas where I live (Seattle area) was quoted at $2.69
for a minimum order amount of 4000 gallons.

The cheapest retail avgas around here is $3.10/gallon (KSHN).
The "average" is around $3.35/gallon.

I just gassed up a few days ago at Scappoose, Oregon for $2.90/gallon.

I get the impression the cost of operating a business in the more
"metropolitan" areas is factored in, but I also get the impression
that in such areas, AvGas is simply priced @ what they think the
market will bear.

I was told by one local FBO owner that local county owned airports /
fuel retailers are not allowed to differ in the price per gallon by
more than $.10 cents (+/-). Where I come from, that's called
price-fixing!

Bela P. Havasreti

Taken directly from the EAA website www.eaa.org and then to the autogas STC
page:


In the opinion of EAA, and in the interest of most conservative operations,
the following observations are offered:

a.. If alcohol content is less than 1%, fuel will probably have no effect
on aircraft.

b.. If fuel contains up to 5% alcohol, caution must be exercised. Do not
permit it to remain in tanks or fuel system more than 24 hours, then drain
and refill with alcohol-free fuel, ensuring that no alcohol concentration
remains in fuel lines or sump. Vapor lock may be a problem. DO NOT FLY.

c.. If alcohol content is more than 5%, DO NOT FLY. Drain fuel system,
flush all parts, replace with clean alcohol-free fuel and run up engine long
enough to exchange fuel in carburetor bowl.

So now the question is posed ... if I take some California gasahol (5.3%)
and dilute it down with 100LL to a 5% concentration, it seems that if I use
it within 24 hours, I can continue to use our gasahol. My calculation says
that 50 gallons of gasahol diluted with 5 gallons of LL would meet the 5%
limitation. Hell, I wouldn't object to running 50-50 if it means I can cut
the lead content in half.

Yet in another place on the website, it says that the gasoline can have NO
alcohol. I'm so confused. {;-)

E'splain to me also why you folks in Wisconsin, Iowa, and the rest of the
midwest are getting your 100LL for $2.50 a gallon or so while I'm paying
$3.50 with the refinery just across the central valley.



Jim
Click to expand...
 
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
"w_tom" <w_tom1@hotmail.com> wrote in message
news:429BA908.2BCF25BC@hotmail.com...

[snip]

My observation is that most bulb failures occur during powerup; whether
or not this is due to the powerup is entirely another matter. The most
probable reason that these failures occur during powerup is that this is
the time when more stress is put on the filament.
Click to expand...
My understanding is that current surge is a main contributing factor
for lamps failing. Cold resistance is lower than warm resistance, so
bulbs often fail when switched on. This is one of the main reasons why
airfield lighting systems use constant current sources with slow
current ramps for switch on.

Fred.
 
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