OT?: Lightbulb life, curiousity

[Kevin Aylward]

You haven't met my ex-wife then?

Ditto the kitchen!

Oh...you have.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Don Klipstein]

I don't know if these are the right places to ask this, but it's the best
I could find on the server. Sorry if it's OT:

I was just thinking today what influences a lightbulb's life more.
They're rated in hours, but I know for a fact they burn out sooner if you
turn them on and off more.

Mostly not true despite the fact that lightbulbs tend to burn out on a
cold start.

What happens is that aging filaments become unable to survive a cold
start just a little while before they become unable to survive continuous
operation. Cold starts generally cause no or very negligible damage
except when fatal.

I explain this in more detail in http://www.misty.com/~don/bulb1.html

A bit of data: I got one of those thermistor type soft starting
"buttons" claimed to double the life of a lightbulb. Even when fully
warmed up, this thing dropped enough voltage to extend the life by 50%
just by dimming the bulb. The reduced current would only result in a
power savings of only about 1.7% but a light output reduction around 10%.

I wonder how it works for lightbulbs, say 40watt. I
assume it would matter more with more wattage because there'd be more
diff. between hot and cold states. So, if you're going to leave the light
off for 2hrs, should you not and leave it on instead? You know, what's
the min. time you'd have to leave it off for before you actually cost life
due to on/off even though you're saving hrs. Hey, you think about these
types of thing while you're sitting on the can! So anybody know?

With most incandescents, a cold start does so little damage that it's
better to turn it off even if for only half a minute.
Another thing - most of the cost of incandescent lighting (of wattages
more than a few watts) is the cost of the electricity, not the cost of the
lightbulbs.

- Don Klipstein ([email protected])

 

[Don Klipstein]

---
Well, considering that the filament _does_ have a thermal time
constant in excess of 8.3ms leads me to believe that being fed with AC
VS DC can't _really_ be likened to power cycling, where the filament
would be expected to be powered on until it reached its normal
operating temperature then powered down and allowed to cool to near
ambient before the cycle repeated.
---


---
That's not totally true, in that local hot spots on the filament tend
to boil off tungsten more quickly at those locations, causing the
filament to "neck down" there and provide high-resistance spots where,
when the filament is turned on, most of the voltage applied to the
cold filament will be dropped, causing that spot to vaporize and the
filament to separate. I'm sure you've noticed that incandescent lamps
almost always fail when they're turned on, precisely for that reason.

So, if the lamp were to be operated continuously, the total number of
lamp-on hours would be greater than if the lamp were operated
intermittently.

Not by much. When a filament develops a neck that cannot survive a cold
start, the neck is suffering extra fast evaporation when running due to it
being hotter than the rest of the filament even in steady operation. This
ill state is accelerating at a rate that increases worse than
exponentially. The filament's hours are already numbered.

One possible significant exception: Halogen lamps, where chemical
processes can cause necks at the end of the filament, where they only
have excessive temperature while the rest of the filament is warming up
and not yet reached full resistance.

- Don Klipstein ([email protected])

 

[Don Klipstein]

I've actually have a carbon filament bulb that I got from Kennedy
Webster in Chicago. Its been burning every night from 6PM to 7PM for
about 7 years now in my front hall . It burns very orange perhaps
~22,000=BA K and it is VERY sensitive to shock and vibration even when
they're cold. These are often used in antique fixtures and it's
suprised me how long it's lasted. I always thought tungsten was
superior.

Consider the efficiency of producing visible light at 2200K. At equal
temperature, tungsten outlasts carbon.

- Don Klipstein ([email protected])

 

[John Fields]

Not by much.

---
Agreed, but the point wasn't about the difference in the length of the
lifetimes, it was that there would have been some life left in the
filament had it not been switched off and then on for the last time.
---

When a filament develops a neck that cannot survive a cold
start, the neck is suffering extra fast evaporation when running due to it
being hotter than the rest of the filament even in steady operation. This
ill state is accelerating at a rate that increases worse than
exponentially. The filament's hours are already numbered.

---
They were from the very first time it was switched on!
---

One possible significant exception: Halogen lamps, where chemical
processes can cause necks at the end of the filament, where they only
have excessive temperature while the rest of the filament is warming up
and not yet reached full resistance.

---
I don't understand that since if they got hotter faster they'd enter
the halogen cycle more quickly and local boil-off would be prevented.
OTOH, since the lead wires are very low R and in intimate thermal
contact with the ends of the filament they may be acting like heat
sinks and keeping the temperature of the ends of the filament lower
than the rest of it until it warms them up. If that's the case, it
may be that the delay of the ends of the filament in entering the
halogen cycle causes excessive boil-off until it gets hot enough to
start working right.

What do you think?

 

[w_tom]

Just had a bulb blow after about 1 hour of operation. Bulbs
fail both during power cycling and during normal operation.
Either way, failure is when the filament is in last hours of
operation - damage has already been done by too many hours of
operation and not due to power cycling.

Yes, evaporation at an eventual hot spot will cause filament
to fail there. However by that time, bulb is well into a
failure mode as indicated by black deposits inside the glass
envelope. Don Klipstein notes how the filament suddenly
fails. Hot spot occurs suddenly at the end of bulb life
expectancy. Once the hot spot starts forming, the bulb is
doomed.

BTW, a light bulb researcher who originally explained this
also provided pictures of the hot spot. One would think the
hot spot would glow brighter. Ironically, the hot spot was
where the filament was darkest. I don't remember why the hot
spot was darker. But then it has been a few decades. The
science of bulb failure has been understood even longer. And
still so many decades later, power cycling is not listed as a
contributing factor - where science and the numbers are first
consulted.

 

[Don Klipstein]

Well,plenty of replies for incandescent bulbs... any replies for compact
flouresents? I know that I shoulden't be putting a flouresent lamp in
the toilets or cupboards, but what about tha hall? the bathroom with a
big family? I hear the "15 minute" rule regularily, but why 15 minutes
and what are the mechanism that reduce life?

There is no one-size-fits-all rule here as in how many minutes does a
compact fluorescent have to stay off or else it would have been more
economical to leave it on.

For one reason, different wattages cost different amounts per minute to
operate, while the cost of the lamp does not vary much with wattage.

Also, some suffer more damage from starting than others.

As for why damage from starting? When the filaments (electrodes) are
not at normal running temperature, the emissive material on them is not
working fully. That results in a higher electric field (voltage gradient)
around the filaments when they are working as cathodes, and positive ions
will bombard the filaments with greater force than normal - and dislodge
atoms of the coating material.

Some are true instant start, which has the lamp operating before the
filaments are warmed up. The lamp may be slightly dimmer while the
filaments are warming up due to higher voltage drop until the
filaments are supporting a "thermionic arc". Some are similar to what is
called "rapid start" with standard fluorescents in the USA, where the lamp
starts glowing while the filaments are being warmed up, but the lamp is
fully on when the filaments get close to normal operating temperature.
Some are "programmed start", where the arc is struck after the filaments
are warmed up. Some have glow switch starting, and usually blink a few
times while starting.
Glow switch ones are the worst for a large number of starts, instant
start is second worst, and program start is the best in terms of damage to
a fluorescent lamp due to starting.

And I have also heard that handeling the glass part will reduce the
number of cycles before the lamp dies... but why?

I have not heard that one. The closest to that I heard is that halogen
bulbs do not like skin oil, salts, ash, alkalis, etc. The compact quartz
bulb/capsule gets extremely hot and is under high stress from high
pressure of the fill gas. Salts and alkalis (including from ash) leach
into quartz at that temperature, causing weak spots and/or stressed spots.

- Don Klipstein ([email protected])

 

[w_tom]

Put a 130 volt light bulb into a 120 volt application - and
double bulb life. Bulbs still fail due to hours of operation
and not due to power cycling. Which light bulbs tend to be
least often replaced LEDs? Orange. Why? Bulbs that power
cycle most are also the bulbs that last longest. Better to
spend big bucks first on LEDs for red and green - that burn
out faster due to hours of operation.

Back to the OP: power cycling does not determine
incandescent bulb life. Bulb life expectancy is determines by
hours of operation, voltage, and mechanical shocks (when
filament is hot).

After so many posts, we only return back to a post that
criticized others for 'feeling' a fact rather than first
learning the numbers. Power cycling does not damage
incandescent bulbs as claimed by Mick Sharpe and tesseract on
28 May 2005.

BTW I wish traffic signal repairmen were so responsive
around here. They completely ignore pedestrian light bulbs.
Previously, statistics estimated when bulbs would fail - and
replace them before failure happens. Problem was that line
voltage does not remain constant. Minor voltage variations
significantly change bulb life expectancy as demonstrated by
previous posted numbers. The 120 volt bulb running at 128
volts lasts only half as long. What voltage is each traffic
signal operating at? Voltage variations caused estimates to
be wrong.

As Michael Terrel demonstrates, a 130 volt bulb running at
120 volts lasts much more than twice as long. Numbers that
demonstrate how to make longer life bulbs. As Michael also
notes, those 130 volt bulbs would only output 75% of light for
120 volt bulbs - would glow more red. And those long life
bulbs would still fail faster is line voltage rises to 125
VAC.

Does applying power slowly extend bulb life? This was a
scam in the 1950s. A little button (temperature changing
resistor) was placed inside an edision socket. What caused
the bulb to last longer? Voltage drop in that button as
demonstrated by numbers provided above. Light bulb lasted
longer and glowed less efficiently. Slowly powering a bulb
does nothing for bulb life expectancy. The button simply
lowered line voltage AND made bulb less efficient.

But its been a few years. A whole new generation is now
ripe to be scammed again - unless that new generation first
learns the numbers.

 

[w_tom]

One factor that determines fluorescent lamp life expectancy
is, again, the filament. Fluorescent bulbs use low pressure
gas whose electrical properties change with contamination. As
the filament (at each end to start the bulb) vaporizes, it
contaminates the gas, thereby increasing startup voltage and
eventual bulb failure.

Another curious fact to extending (some) fluorescent bulb
life expectancy was to maintain a small current through
startup filaments. It was never explained in that paper why
such currents extend bulb life nor provided numbers to
demonstrate the effect.

Of course numbers change for different types of
fluorescent. Even though fluorescent bulbs were developed
before incandescent bulbs, the science inside a fluorescent
bulb is significantly more complex. Once tried to apply those
equations to a series of inert gas bulbs. Never did succeed.
But then even material used in the electrode causes changes to
the equations. Fluorescent bulbs are significantly more
complex.

 

[Don Klipstein]

The halogen cycle does not prevent evaporation - it returns evaporated
tungsten to the filament, and does not do an especially good job at
returning it where it is most needed.

The main reason that halogen lamps last longer than non-halogens with
the same filament temperature is that in halogens, the fill gas pressure
is much higher. This slows evaporation of the filament. The small size,
thicker walls and higher strength of the quartz (or specialized glass in
many cases) bulb/capsule permit a much higher fill gas pressure.
The halogen cycle does achieve some life extension, but not a whole lot
because the halogen cycle is not good at depositing more tungsten where it
is needed most. One thing the halogen cycle is needed for is keeping the
inner surface of the wall/capsule clean of tungsten - with the small area,
that surface would otherwise blacken quickly.
Another factor that many (but not all) halogen lamps benefit from: With
the small size of the bulb/capsule and higher cost, the cost does not get
much worse from using krypton instead of argon as a main fill gas
ingredient.

OTOH, since the lead wires are very low R and in intimate thermal
contact with the ends of the filament they may be acting like heat
sinks and keeping the temperature of the ends of the filament lower
than the rest of it until it warms them up. If that's the case, it
may be that the delay of the ends of the filament in entering the
halogen cycle causes excessive boil-off until it gets hot enough to
start working right.

What do you think?

I think that a neck near the end of the filament, due to less mass,
warms up faster than the rest of the filament and can overshoot in
temperature when the rest of the filament is not yet warmed up. And
heatsinking is just enough to have the temperature a little lower than
that of the rest of the filament in steady operation. That's what I think
happens.

- Don Klipstein ([email protected])

 

[w_tom]

Early designs did this 'keep lamp warm' so that the initial
power on current (on the order of seven times normal current)
was not so destructive to transistors that controlled the
bulb. A warmer bulb does not have the larger power on current
that would harm a driver transistor.

 

[Don Klipstein]

One factor that determines fluorescent lamp life expectancy
is, again, the filament. Fluorescent bulbs use low pressure
gas whose electrical properties change with contamination. As
the filament (at each end to start the bulb) vaporizes, it
contaminates the gas, thereby increasing startup voltage and
eventual bulb failure.

Filament material does not contaminate the gas - it condenses on the
inner surface of the bulb.

Another curious fact to extending (some) fluorescent bulb
life expectancy was to maintain a small current through
startup filaments. It was never explained in that paper why
such currents extend bulb life nor provided numbers to
demonstrate the effect.

Can you cite the paper that claims this happens even without explaining
why?

In fluorescent lamps, the usual failure is not from the filaments
breaking, but from the emissive coating being worn away. Some
fluorescents (main example - rapid start) have power applied to the
filaments during operation and I have heard a couple times that some of
these have reduced life if the filament power is removed during operation,
but I have not heard of fluorescents lasting longer if the filaments are
kept warm while they are off.

- Don Klipstein ([email protected])

 

[w_tom]

This claim that a filament with a few milliamps of current
through it would last longer has always struck me odd. I
mention it because it came from a reputable source, because
details were not provided, and because I always remained
curious. Unfortunately I believe it was a manufacturer's
paper that has since been gone for a few decades; don't
remember the source. The paper noted factors that effective
lamp life expectancy. It defined that filament current in
terms of single digit voltage - too much or too little caused
less improvement. I mention it, in part, that others may
provide additional information. This puzzling nature for some
fluorescents has always left me curious.

Basic equations for physics on designing fluorescant lamps
noted that gas contamination contributes to bulb failure;
changed constants in that equation. BTW, one needs a library
well predating WWII to find these gaseous physics books. We
demonstrated this electrode contamination when designing a
custom fixture to light multiple bulbs using different inert
gases. Too much current caused electrodes (or filament
depending on bulb) to contaiminate the gas thereby changing
its electrical characteristics enough to become bulb
failure. Of course "emissive coating being worn away" would
also be same as gas contamination. Another factor that
changes the equation is gas pressure. If that coating goes
somewhere, does it change tube pressure? As noted earlier,
even the equations are quite complex. Never did get the
equations to work. Ended up resorting to a 'trial and error'
method.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Well,plenty of replies for incandescent bulbs... any replies for compact
flouresents? I know that I shoulden't be putting a flouresent lamp in


Flourescents? If you expect answers, try spelling it fluorescents.

the toilets or cupboards, but what about tha hall? the bathroom with a
big family? I hear the "15 minute" rule regularily, but why 15 minutes
and what are the mechanism that reduce life? And I have also heard that
handeling the glass part will reduce the number of cycles before the
lamp dies... but why?



Mel

[email protected] a écrit :

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

[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.

 

[Don Klipstein]

This claim that a filament with a few milliamps of current
through it would last longer has always struck me odd. I
mention it because it came from a reputable source, because
details were not provided, and because I always remained
curious. Unfortunately I believe it was a manufacturer's
paper that has since been gone for a few decades; don't
remember the source. The paper noted factors that effective
lamp life expectancy. It defined that filament current in
terms of single digit voltage - too much or too little caused
less improvement. I mention it, in part, that others may
provide additional information. This puzzling nature for some
fluorescents has always left me curious.

Basic equations for physics on designing fluorescant lamps
noted that gas contamination contributes to bulb failure;
changed constants in that equation. BTW, one needs a library
well predating WWII to find these gaseous physics books. We
demonstrated this electrode contamination when designing a
custom fixture to light multiple bulbs using different inert
gases. Too much current caused electrodes (or filament
depending on bulb) to contaiminate the gas thereby changing
its electrical characteristics enough to become bulb
failure. Of course "emissive coating being worn away" would
also be same as gas contamination. Another factor that
changes the equation is gas pressure. If that coating goes
somewhere, does it change tube pressure?

It does not significantly even temporarily, let alone permanenetly,
since the vapors of the coating don't stay vaporized long but condense on
the inner surface of the bulb rather quickly.

As for gaseous contaminants - usually things work more the other way
around. Fluorescent lamps tend to get those during manufacture or (more
likely in the case of lower quality lamps) when the lamp is first
operated, and operation after that tends to have gaseous contaminants
removed by chemically reacting with the filaments more than add more
contaminants.

One thing that happens in a few discharge lamps (mostly other than
fluorescent) is with a neon-argon mixture that is mostly neon - often
99.5% neon .5% argon: Argon ions dig their way into the inner surface of
the bulb and the argon gets stuck there, resulting in a loss of argon.
Starting becomes more difficult when this happens. I have heard of this
being a problem with some low pressure sodium lamps.

But when a neon glow lamp running from 120V AC starts flickering, this
is not the problem since the ones that flicker when they get old use pure
neon, and ones with neon-argon mixture tend to just fade from blackening
of the bulb. Ones with pure neon I believe start this flickering
business when a coating on the electrodes being worn away while ones with
a bit of argon can keep glowing steadily although dimmed by bulb
blackening.

- Don Klipstein ([email protected])

 

[Mel]

Watson A.Name - "Watt Sun, the Dark Remover" a écrit :

Well,plenty of replies for incandescent bulbs... any replies for compact
flouresents? I know that I shoulden't be putting a flouresent lamp in


Flourescents? If you expect answers, try spelling it fluorescents.

Sorry, it slipped through.... but not everyone is a native English
speaker here, and spelling errors are bound to happen - my spell checker
didn't detect the error either, and google didn't really mind either (13
300 hits with the wrong spelling - I'm not the only one!). Doesn't seem
to have bothered anyone else....



Mel

 

[Fred McGalliard]

....

No science fact says power cycling is destructive, as
claimed.

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.

 

[Fred McGalliard]

....

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.

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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On Mon, 30 May 2005 12:15:02 -0700, "RST Engineering"

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

 

[Fred Stevens]

[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.

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.