OT?: Lightbulb life, curiousity

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. Kinda like a HDD, but to way less extent.
But, how far does that extend.. a HDD I've heard lasts longest if it's
on/off 1x/day, assuming you're going to sleep and/or not use it for at
least 10-12hrs. 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?
--
_____________________________________________________
For email response, or CC, please mailto:see.my.sig.4.addr(at)bigfoot.com.
Yeah, it's really a real address

 

[Mick Sharpe]

When you switch on an incandescent lamp, some the tungsten that the filament
is made of evaporates and remains in a gaseous state until the lamp is
switched off, when the tungsten gas will condense out. Unfortunately, since
the envelope of the bulb offers a much greater surface area than the
filament, the gas condenses onto the bulb, where it remains. As you switch
the lamp on and off, metal slowly migrates from the filament to the bulb
envelope, turning it black. Eventually, the filament becomes too thin to
accomodate the supplied current and the lamp 'blows'.

As to your optimisation problem, this should probably be addressed to
sci.maths where I am sure it will cause a good deal of head scratching.

 

[w_tom]

Power cycling has virtually no effect on light bulb life
expectancy. Factors that determine life expectancy are
filament temperature (ie voltage) and vibration (when filament
is hot). If power cycling adversely affected light bulb life,
then orange lights on traffic signals - flashing all night -
would be the first to fail. Reality is completely different.
Hours of operation - be it the red, green, or orange-
determine light bulb life expectancy. Power cycling only
affects life expectancy when the human uses feeling rather
than first learn facts.

No science fact says power cycling is destructive, as
claimed. But so many will believe without first demanding the
numbers. Show me? Junk science concepts such as 'power
cycling damage' can't provide those numbers. Why? For some,
feelings are good enough to proclaim a fact. No wonder so
many people believe and worship Rush Limbaugh.

Take a 120 volt light bulb. Increase the line voltage to
128 volts. What happens to bulb life expectancy? Bulb lasts
only 50% of its predicted life. Notice new here. The
industry benchmark for such information is the IES Lighting
Handbook. If power cycling was so destructive, then those
making such claims can cite that fact from the IES.

Those who want honest facts will appreciate why filament
vaporizes. The relationship between line voltage and life
expectancy is an inverse exponential to the power of 13. How
do you know which is accurate? Only one cites both a source
AND the numbers. Power cycling is destructive only when myths
and personal feelings replace science.

see.my.sig.4.addr@nowhere.com.invalid wrote:

...
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. Kinda like a HDD, but to way
less extent. But, how far does that extend.. a HDD I've heard lasts
longest if it's on/off 1x/day, assuming you're going to sleep
and/or not use it for at least 10-12hrs. 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?

 

[w_tom]

All good and nice as long as one doesn't first ask questions
such as why? Assumed is that a bulb lasted due to no power
cycling - using reasoning in direct violation of well proven
industry science.

Take a 120 volt light bulb rated for 1500 hours. Illuminate
it with 85 volts. How long will it last? About 15 years -
running continuously. Longer if power cycled. So why did
that bulb last 20 years? One simply wildly speculated - no
power cycling - and then declard that speculation as fact.
Speculated in direct contradiction to numbers and facts
published generations ago.

Which has more credibility? One who speculates only because
of an observation? Or one who learns how light bulbs fail AND
learns the well proven industry numbers? Junk science is
characterized by no numbers and incomplete speculation. Junk
science says power cycling damages light bulbs. If true, then
where are industry citations that support that claim?
Industry makes no such claim. Some people just know because
they saw something and then speculated. At best, that
speculation does not even qualify as a theory. However, they
then push that specualtion as if it were fact.

No numbers further demonstrates that power cycling damage is
a myth. Filament temperature, as defined by voltage,
determines a bulb's life expectancy. Numbers provided in the
other post.

tesseract wrote:

Quite true, and there are additional factors. Heating and cooling
add stress. If the filament is a coil, it is an inductor, and AC
self inductance will cause it to flex, it possibly being less
flexible when it is cool. There may be additional factors yet.
Fluorescent bulbs are now fairly cheap, and power leds are just
over the horizon, available but pricey. Both convert more of the
electrical energy into light rather than heat. I know that some
exceptional incandescents that were never turned off lasted over
twenty years.

 

[w_tom]

Using Mick Sharpe's reasoning, we then ask how to extend the
life of an incandescent bulb. Light bulbs on 60 Hz
electricity power cycle 120 times per second. Therefore if we
power the bulb with DC electricity, then no power cycling.
Therefore the bulb must last longer because some the tungsten
no longer evaporates and remains in a gaseous state until the
lamp is switched off 120 times per second.

Then we apply experimental evidence. A bulb at 120 VDC
lasts same as a bulb at 120 VAC RMS. Why? Voltage and hours
of operation - not power cycling - determine bulb life
expectancy.

Next, someone will claim that the speed of power on affects
bulb life expectancy. Somehow they just know even without
science based facts, citation, or numbers. No wonder the
president could lie about weapons of mass destruction and so
many blindly believed him. Feeling is now sufficient to
declare something as fact.

Mick Sharpe wrote:

When you switch on an incandescent lamp, some the tungsten that the filament
is made of evaporates and remains in a gaseous state until the lamp is
switched off, when the tungsten gas will condense out. Unfortunately, since
the envelope of the bulb offers a much greater surface area than the
filament, the gas condenses onto the bulb, where it remains. As you switch
the lamp on and off, metal slowly migrates from the filament to the bulb
envelope, turning it black. Eventually, the filament becomes too thin to
accomodate the supplied current and the lamp 'blows'.

As to your optimisation problem, this should probably be addressed to
sci.maths where I am sure it will cause a good deal of head scratching.

 

[John Fields]

On Sat, 28 May 2005 19:18:57 -0400, w_tom <w_tom1@hotmail.com> wrote:

Using Mick Sharpe's reasoning, we then ask how to extend the
life of an incandescent bulb. Light bulbs on 60 Hz
electricity power cycle 120 times per second. Therefore if we
power the bulb with DC electricity, then no power cycling.
Therefore the bulb must last longer because some the tungsten
no longer evaporates and remains in a gaseous state until the
lamp is switched off 120 times per second.

---
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.
---

Then we apply experimental evidence. A bulb at 120 VDC
lasts same as a bulb at 120 VAC RMS. Why? Voltage and hours
of operation - not power cycling - determine bulb life
expectancy.

---
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.
---

Next, someone will claim that the speed of power on affects
bulb life expectancy. Somehow they just know even without
science based facts, citation, or numbers. No wonder the
president could lie about weapons of mass destruction and so
many blindly believed him. Feeling is now sufficient to
declare something as fact.

---
Stick to the facts and keep your opinions and your politics to
yourself.

--
John Fields
Professional Circuit Designer

 

[Mick Sharpe]

Many thanks for your most courteous correction. I sometimes wonder what I'm
doing here answering honest questions as well as I can

"w_tom" <w_tom1@hotmail.com> wrote in message
news:4298F92B.BA101869@hotmail.com...

Power cycling has virtually no effect on light bulb life
expectancy. Factors that determine life expectancy are
filament temperature (ie voltage) and vibration (when filament
is hot). If power cycling adversely affected light bulb life,
then orange lights on traffic signals - flashing all night -
would be the first to fail. Reality is completely different.
Hours of operation - be it the red, green, or orange-
determine light bulb life expectancy. Power cycling only
affects life expectancy when the human uses feeling rather
than first learn facts.

No science fact says power cycling is destructive, as
claimed. But so many will believe without first demanding the
numbers. Show me? Junk science concepts such as 'power
cycling damage' can't provide those numbers. Why? For some,
feelings are good enough to proclaim a fact. No wonder so
many people believe and worship Rush Limbaugh.

Take a 120 volt light bulb. Increase the line voltage to
128 volts. What happens to bulb life expectancy? Bulb lasts
only 50% of its predicted life. Notice new here. The
industry benchmark for such information is the IES Lighting
Handbook. If power cycling was so destructive, then those
making such claims can cite that fact from the IES.

Those who want honest facts will appreciate why filament
vaporizes. The relationship between line voltage and life
expectancy is an inverse exponential to the power of 13. How
do you know which is accurate? Only one cites both a source
AND the numbers. Power cycling is destructive only when myths
and personal feelings replace science.

see.my.sig.4.addr@nowhere.com.invalid wrote:
...
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. Kinda like a HDD, but to way
less extent. But, how far does that extend.. a HDD I've heard lasts
longest if it's on/off 1x/day, assuming you're going to sleep
and/or not use it for at least 10-12hrs. 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?

 

[w_tom]

Being politically correct is akin to lying for a self
serving gain. I am not politically correct; have no interest
in being so corrupt. Mick Sharpe obviously was not insulted
if the objective is accurate facts.

Fact remains that incandescent life expectancy is a function
of filament temperature (voltage) and other environmental
factors such as mechanical shock when filament is hot. This
assumes a statistically average bulb; making manufacturing
defects (ie hot spots created by a production defect)
irrelevant. The underlying point is why some promote myths
not based upon science.

Again the lessons of history are cited. Many even believe
lying politicians who don't provide numbers - be it Saddam's
weapons of mass destruction, or people of German ancestry
persecuted in Checkoslavakia. Either way, its called
propaganda. How do politicians, et al get away with lies? No
numbers. No responsible sources. And people who just blindly
believe these lies because it is the first thing they are
told. Beliefs based upon emotion rather than first demanding
supporting numbers and facts. Again, it's called
propaganda. A glaring symptom of propaganda is no numbers. If
they provided numbers, then their lies could be easily
exposed.

No insults posted or intended. Just a blunt fact about
light bulb life expectancy and similar examples from history.

Mick Sharpe wrote:

Many thanks for your most courteous correction. I sometimes wonder
what I'm doing here answering honest questions as well as I can

 

[Mick Sharpe]

"w_tom" <w_tom1@hotmail.com> wrote in message
news:42993923.9769380A@hotmail.com...

No insults posted or intended. Just a blunt fact about
light bulb life expectancy and similar examples from history.

It is your bluntness, Sir, that is the problem

 

[Mick Sharpe]

"tesseract" <helixburger@yahoo.com> wrote in message
news:1117360313.826553.82890@g14g2000cwa.googlegroups.com...

Let's try for more light and less heat.

Amen to that!

Tungsten halogen, or cold cathode?

 

[John Fields]

On Sat, 28 May 2005 23:38:11 -0400, w_tom <w_tom1@hotmail.com> wrote:

Fact remains that incandescent life expectancy is a function
of filament temperature (voltage) and other environmental
factors such as mechanical shock when filament is hot. This
assumes a statistically average bulb; making manufacturing
defects (ie hot spots created by a production defect)
irrelevant. The underlying point is why some promote myths
not based upon science.

---
Your relegation of the hot spots to irrelevance because they don't fit
into your preconceived notion of how a "statistically average"
filament should behave is disingenuous and is being used as a point
from which you can segue into a political diatribe. The _fact_ is
that it's precisely the anomalies in the filament which lead to the
creation of hot spots, i.e. its inhomogeneity, which causes turn-on
failure. As you've been told several times, this is _not_ the venue
where your political spew is welcome, so take it somewhere else.

--
John Fields
Professional Circuit Designer

 

[Mick Sharpe]

I'm interested to know when deposition of the filament metal on the bulb
envelope actually occurs, assuming that it is filament metal that turns the
bulb black. Is it whilst the lamp is switched on and in a pretty much
equilibrium state, or is it during turn-on when the lamp is warming up, or
turn-off when it is cooling down, as I have been led to believe? Anyone know
or have an opinion?

 

[m II]

stratus46@yahoo.com wrote:

And where are your numbers ?
troll ?

Funny how he sounds identical to Gimminy Boob and John P* Bengi, those fountains
of misinformation.



mike

 

[John Fields]

On Sun, 29 May 2005 13:40:15 +0000 (UTC), "Mick Sharpe"
<mick.sharpe@btinternet.com> wrote:

I'm interested to know when deposition of the filament metal on the bulb
envelope actually occurs, assuming that it is filament metal that turns the
bulb black. Is it whilst the lamp is switched on and in a pretty much
equilibrium state, or is it during turn-on when the lamp is warming up, or
turn-off when it is cooling down, as I have been led to believe? Anyone know
or have an opinion?

---
A conventional (non - halogen) incandescent lamp is _never_ in a state
of equilibrium when it's operating because there is no mechanism in
place to return the evaporated tungsten to the filament. Instead,
since the envelope is cooler than the filament, the tungsten
evaporated from the filament condenses on the inner wall of the
envelope, blackening it. As a consequence of the evaporation of the
tungsten, the filament narrows because of the metal it's lost.
Because of impurities in the tungsten some spots on the filament "boil
off" more metal than others, causing those spots to narrow more than
others, eventually causing a failure to occur at the weakest spot.

In order for an incandescent lamp to run more nearly in equilibrium
(that is, for the rate of metal being returned to the filament to
equal the amount of metal leaving the filament), a halogen is used in
the fill gas. For more detail, Google "halogen cycle" or go here:

http://www.goodmart.com/facts/light_bulbs/halogen_cycle.aspx

--
John Fields
Professional Circuit Designer

 

[Pig Bladder]

On Sun, 29 May 2005 11:42:36 +0000, Mick Sharpe wrote:

"tesseract" <helixburger@yahoo.com> wrote in message
news:1117360313.826553.82890@g14g2000cwa.googlegroups.com...
Let's try for more light and less heat.

Amen to that!

Tungsten halogen, or cold cathode?

Less Fililng!
--
The Pig Bladder from Uranus

 

[Rich Grise]

On Sun, 29 May 2005 15:44:48 +0000, Mick Sharpe wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
A conventional (non - halogen) incandescent lamp is _never_ in a state
of equilibrium when it's operating because there is no mechanism in
place to return the evaporated tungsten to the filament. Instead, since
the envelope is cooler than the filament, the tungsten evaporated from
the filament condenses on the inner wall of the envelope, blackening it.
As a consequence of the evaporation of the tungsten, the filament
narrows because of the metal it's lost. Because of impurities in the
tungsten some spots on the filament "boil off" more metal than others,
causing those spots to narrow more than others, eventually causing a
failure to occur at the weakest spot.

If metal is evaporated continuously while the lamp is in operation, may I
conclude that the idea that power cycling affects lamp life is an old
wives tale, at least as far as evaporative metal transfer is concerned?

Well, you can draw any conclusion(s) that you want, but considering the
dramatic positive temperature coefficient of resistance of tungsten, it
can be shown that at turn-on, given a constant voltage supply, the
filament passes more than its rated current. This current is equal
throughout the filament (each part of the filament is in series with
all of the other parts), but because of discontinuities in the tungsten
itself, whether they be manufacturing tolerances, inhomogeneities in
the alloy, or grain boundaries, different portions of the filament
will almost surely develop different voltages from each other, dissipating
different amounts of power.

So, because of that power differential, the higher-resistance parts of
the filament get hotter than the rest, and the tungsten boils off just
a little bit faster. This has a positive-feedback effect, in that each
hot spot will continue to get hotter - the loss of tungsten causes a
decrease in the cross-section of the filament wire, further increasing
that segment's resistance, increasing that segment's share of the voltage
drop, increasing the power dissipation and so temperature of that segment,
making it boil the tungsten off faster, and so on, until one day, the
inrush current, dropped primarily across the hottest hot spot, causes
that segment of the filament to reach the melting point of tungsten,
and "tink" - dead light bulb.

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. ;-)

If you have an application where the bulb needs to turn on and off a
lot, like, for instance, an incandescent jumbotron, or some kind of
digital display, bulb life can be increased dramatically by never
turning off the bulb completely, but bypassing the switch with a resistor
such that the filament is kept warm - just below the dull red glow is a
pretty good compromise. This is also well-documented, i.e., "fact". ;-)

Hope This Helps!
Rich

 

[John Fields]

On Sun, 29 May 2005 15:44:48 +0000 (UTC), "Mick Sharpe"
<mick.sharpe@btinternet.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:dulj91d8gghccd6tno9ir8qpmhq1dv8utq@4ax.com...
On Sun, 29 May 2005 13:40:15 +0000 (UTC), "Mick Sharpe"
mick.sharpe@btinternet.com> wrote:
A conventional (non - halogen) incandescent lamp is _never_ in a state
of equilibrium when it's operating because there is no mechanism in
place to return the evaporated tungsten to the filament. Instead,
since the envelope is cooler than the filament, the tungsten
evaporated from the filament condenses on the inner wall of the
envelope, blackening it. As a consequence of the evaporation of the
tungsten, the filament narrows because of the metal it's lost.
Because of impurities in the tungsten some spots on the filament "boil
off" more metal than others, causing those spots to narrow more than
others, eventually causing a failure to occur at the weakest spot.

If metal is evaporated continuously while the lamp is in operation, may I
conclude that the idea that power cycling affects lamp life is an old wives
tale, at least as far as evaporative metal transfer is concerned?

---
Even though it seems that should be the case, I don't have any
first-hand information or verifiable data that it is. IOW, I think so
but I don't know for sure.
---

Thanks for the link, BTW

---
You're welcome.


--
John Fields
Professional Circuit Designer

 

[Mick Sharpe]

"John Fields" <jfields@austininstruments.com> wrote in message
news:dulj91d8gghccd6tno9ir8qpmhq1dv8utq@4ax.com...

On Sun, 29 May 2005 13:40:15 +0000 (UTC), "Mick Sharpe"
mick.sharpe@btinternet.com> wrote:
A conventional (non - halogen) incandescent lamp is _never_ in a state
of equilibrium when it's operating because there is no mechanism in
place to return the evaporated tungsten to the filament. Instead,
since the envelope is cooler than the filament, the tungsten
evaporated from the filament condenses on the inner wall of the
envelope, blackening it. As a consequence of the evaporation of the
tungsten, the filament narrows because of the metal it's lost.
Because of impurities in the tungsten some spots on the filament "boil
off" more metal than others, causing those spots to narrow more than
others, eventually causing a failure to occur at the weakest spot.

If metal is evaporated continuously while the lamp is in operation, may I
conclude that the idea that power cycling affects lamp life is an old wives
tale, at least as far as evaporative metal transfer is concerned?

Thanks for the link, BTW

 

[John Fields]

On Sun, 29 May 2005 16:42:57 GMT, Pig Bladder
<pigbladder@neodruid.net> wrote:

On Sun, 29 May 2005 11:42:36 +0000, Mick Sharpe wrote:


"tesseract" <helixburger@yahoo.com> wrote in message
news:1117360313.826553.82890@g14g2000cwa.googlegroups.com...
Let's try for more light and less heat.

Amen to that!

Tungsten halogen, or cold cathode?

Less Fililng!

---
Piggy,

Have you ever considered correcting your mistakes _before_ you hit
send?^)


--
John Fields
Professional Circuit Designer

 

[Pig Bladder]

On Sun, 29 May 2005 12:53:32 -0500, John Fields wrote:

On Sun, 29 May 2005 16:42:57 GMT, Pig Bladder <pigbladder@neodruid.net
wrote:

On Sun, 29 May 2005 11:42:36 +0000, Mick Sharpe wrote:


"tesseract" <helixburger@yahoo.com> wrote in message
news:1117360313.826553.82890@g14g2000cwa.googlegroups.com...
Let's try for more light and less heat.

Amen to that!

Tungsten halogen, or cold cathode?

Less Fililng!

---
Piggy,

Have you ever considered correcting your mistakes _before_ you hit
send?^)

Of course not. Only people from Earth do that.
--
The Pig Bladder from Uranus