Metal content Tungsten.

http://www.pddnet.com/news-regular-l...ippers-060209/



Thank You,
Randy

Remove 333 from email address to reply.

On Jun 2, 8:01*pm, Randy wrote:
Metal content Tungsten.

http://www.pddnet.com/news-regular-l...nto-power_sipp...

Thank You,
Randy

Remove 333 from email address to reply.

Neat. Sounds like the process would work well for a lot of things.
Solar Collectors, stealth airplanes.

Dan

Randy wrote:
Metal content Tungsten.

http://www.pddnet.com/news-regular-l...ippers-060209/

You can increase the intensity and shift the color of any incandescent
bulb into the blue region while reducing relative power just by using a
thinner filament. That process reduces bulb lifetime however.
The following cites indicate that there is a downside to using a laser
to thin a filament.

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

"In flood lamps used for photographic lighting, the tradeoff is made in the
other direction. Compared to general-service bulbs, for the same power, these
bulbs produce far more light, and (more importantly) light at a higher color
temperature, at the expense of greatly reduced life (which may be as short as
2 hours for a type P1 lamp)."

--Winston -- Goofed around with light bulbs as a kid.

--

We now return you to the economic collapse, already in progress.

On Tue, 02 Jun 2009 13:37:07 -0700, Winston
wrote:

Randy wrote:
Metal content Tungsten.

http://www.pddnet.com/news-regular-l...ippers-060209/

You can increase the intensity and shift the color of any incandescent
bulb into the blue region while reducing relative power just by using a
thinner filament. That process reduces bulb lifetime however.
The following cites indicate that there is a downside to using a laser
to thin a filament.

http://en.wikipedia.org/wiki/Incande...b#cite_note-24


I understood the article to say not that the filament is thinned, but
that its surface is modified to increase emissivity.

I've got a prototype on my desk of some rebuildable lamps I designed
and built a couple years ago for a customer who was doing similar
research. They disassemble easily so new filaments can be mounted, and
have cute plumbing and electrical feedthroughs for thorough purging.
The most surprising part of the project, which I think I've mentioned
here before, was obtaining a small quantity of getter. One of the
ingredients in the getter for incandescent lamps is red phosphorous,
which is apparently strictly controlled these days because it's used
in cooking meth.

--
Ned Simmons

Ned Simmons wrote:

(...)

I understood the article to say not that the filament is thinned, but
that its surface is modified to increase emissivity.

Chunlei Guo:

"We fired the laser beam right through the glass of the bulb and
altered a small area on the filament. When we lit the bulb, we
could actually see this one patch was clearly brighter than the
rest of the filament."

Sounds to me as if the modification was just redistribution of
filament metal. What would happen when you increase the resistance
of a portion of a filament by thinning it? It dissipates more power
because it's resistance is higher (P=I^2R) It glows more brightly
than the rest of the filament but will cause the bulb to fail much
earlier than it would have without the modification, I think.
Would Occam be pleased with this guess?

I've got a prototype on my desk of some rebuildable lamps I designed
and built a couple years ago for a customer who was doing similar
research. They disassemble easily so new filaments can be mounted, and
have cute plumbing and electrical feedthroughs for thorough purging.
The most surprising part of the project, which I think I've mentioned
here before, was obtaining a small quantity of getter. One of the
ingredients in the getter for incandescent lamps is red phosphorous,
which is apparently strictly controlled these days because it's used
in cooking meth.

That'll be the thing I learned today.

--Winston


--

We now return you to the economic collapse, already in progress.

On Tue, 02 Jun 2009 20:18:57 -0700, Winston wrote:



Sounds to me as if the modification was just redistribution of
filament metal. What would happen when you increase the resistance
of a portion of a filament by thinning it? It dissipates more power
because it's resistance is higher (P=I^2R) It glows more brightly
than the rest of the filament but will cause the bulb to fail much
earlier than it would have without the modification, I think.
Would Occam be pleased with this guess?


I got the impression that the object was to "roughen" the surface. This would
make the tungsten a better emitter. As they said, if you have good control of
the size and spacing of the asperities, you will be able to selectively change
the emissivity for different colours. If they merely wanted to selectively
thin the filament, it would be orders of magnitude cheaper to do it when
drawing the wire. Conventional bulb can (and are, for some types) be made more
efficient by using a dichroic reflector so that much of the IR gets bounced
back to the filament rather than heating the rest of the world.



Mark Rand
RTFM

Mark Rand wrote:

(...)

I got the impression that the object was to "roughen" the surface. This would
make the tungsten a better emitter. As they said, if you have good control of
the size and spacing of the asperities, you will be able to selectively change
the emissivity for different colours.

"Though Guo cannot yet make a simple bulb shine pure blue, for instance, he can
change the overall radiated spectrum so that the tungsten, which normally
radiates a yellowish light, could radiate a more purely white light."

You can do the same thing without a laser. Just push more power into the
bulb and the color temperature will shift upward. Bulb life suffers, though.

If they merely wanted to selectively
thin the filament, it would be orders of magnitude cheaper to do it when
drawing the wire.

OK, but how do I justify this nifty femtosecond pulsed laser then?

Gotta stay focused on the goal here. VBG

Creation of that roughened surface means redistributing filament
tungsten, yes? Subtract some here, add some there?

I'll bet you a dollar that we don't hear anything from Chunlei Guo or
University of Rochester regarding bulb life tests.

--Winston

--

We now return you to the economic collapse, already in progress.

On Tue, 02 Jun 2009 20:18:57 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

I understood the article to say not that the filament is thinned, but
that its surface is modified to increase emissivity.

Chunlei Guo:

"We fired the laser beam right through the glass of the bulb and
altered a small area on the filament. When we lit the bulb, we
could actually see this one patch was clearly brighter than the
rest of the filament."

Sounds to me as if the modification was just redistribution of
filament metal. What would happen when you increase the resistance
of a portion of a filament by thinning it? It dissipates more power
because it's resistance is higher (P=I^2R) It glows more brightly
than the rest of the filament but will cause the bulb to fail much
earlier than it would have without the modification, I think.
Would Occam be pleased with this guess?


If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."

--
Ned Simmons

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."

Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

--Winston

--

We now return you to the economic collapse, already in progress.

On Jun 2, 9:37*pm, Winston wrote:

You can increase the intensity and shift the color of any incandescent
bulb into the blue region while reducing relative power just by using a
thinner filament. *
--Winston *-- Goofed around with light bulbs as a kid.

True, but the article was about changing the emissivity of the
filament. Note the article started with how they changed the
adsorption of aluminum so that it reflected no light by modifying the
surface so that it had grooves with their size in the order of the
light waves. Then went on to how they were able to make metals have
different colors. So if one modified the surface of the filament so
that it would radiate less IR and more visible light, the light bulb
be more efficient.


Dan

On Wed, 03 Jun 2009 20:49:44 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."

Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

As I said above, if the experiment created a hot spot by thinning the
filament the resistance of the filament, and the power consumed, would
change. The experimenters reported there was *no change* in the power
consumption.

The relationship between power density, temperature, efficiency and
life is well understood -- you can find it in old texts that date back
to the early days of electric lighting. It's hard to believe that
these guys, whose previous work involved fiddling with the emissivity
of metals, are unaware of that relationship and have misinterpreted
the results of their experiment.

--
Ned Simmons

Ned Simmons wrote:
On Wed, 03 Jun 2009 20:49:44 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."
Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

As I said above, if the experiment created a hot spot by thinning the
filament the resistance of the filament, and the power consumed, would
change. The experimenters reported there was *no change* in the power
consumption.

In *net* consumption, no change was detected. I get that.
I hypothesize that the local power consumption at the thinned area of the
filament did increase, because it's increased resistance dropped more voltage
across the thinned area for a given amount of current. The increased resistance
of the filament as a whole would have decreased the filament current a tiny
amount, cancelling the effect of the local power consumption increase.

Model it as two PTC resistors in series, one of which is about a percent of the
value of the second one. Triple the value of the smaller resistance and it's
power consumption triples. The net resistance of the network as a whole is
decreased by a couple percent, causing the second resistor to decrease in value.
As a result, current increases once again and a new equilbrium is established
which is very close, if not identical to the pre-modification current.
The bulb lifetime is significantly decreased but the study did not encompass
bulb lifetime, just hotspots and spectral shift.

The relationship between power density, temperature, efficiency and
life is well understood -- you can find it in old texts that date back
to the early days of electric lighting. It's hard to believe that
these guys, whose previous work involved fiddling with the emissivity
of metals, are unaware of that relationship and have misinterpreted
the results of their experiment.

They didn't misinterpret, as far as I can see.
They didn't say a word about the post-modification reliability of the bulb.
You could argue that they committed an error of omission about that, if you
were feeling very charitable.


--Winston

--

We now return you to the economic collapse, already in progress.

wrote:
On Jun 2, 9:37 pm, Winston wrote:

You can increase the intensity and shift the color of any incandescent
bulb into the blue region while reducing relative power just by using a
thinner filament.
--Winston -- Goofed around with light bulbs as a kid.

True, but the article was about changing the emissivity of the
filament.

I respectfully disagree. The article was about changing the
power distribution ratio and spectral shift in various parts
of the filament. Our researchers cleverly implied that
changing the thickness of a metal oxide layer (and the resulting
emissivity changes) had something to do with the changes
in the light bulb but the two effects are quite different and
have nothing to do with each other, IMHO.

The filament is in a vacuum. Heating it does not cause it's
surface to mix more readily with oxygen because there is no
oxygen to speak of, in the vicinity of the filament.

Note the article started with how they changed the
adsorption of aluminum so that it reflected no light by modifying the
surface so that it had grooves with their size in the order of the
light waves. Then went on to how they were able to make metals have
different colors.

Sure! Anyone who has held a torch to steel has seen how the surface
changes the color of reflected light.


So if one modified the surface of the filament so
that it would radiate less IR and more visible light, the light bulb
be more efficient.

Theoretically, I agree. This isn't what our researchers were doing,
however.

--Winston


--

We now return you to the economic collapse, already in progress.

On Jun 5, 3:03*am, Winston wrote:


I respectfully disagree.
*Our researchers cleverly implied that
changing the thickness of a metal oxide layer (and the resulting
emissivity changes) had something to do with the changes
in the light bulb but the two effects are quite different and
have nothing to do with each other, IMHO.

The filament is in a vacuum. Heating it does not cause it's
surface to mix more readily with oxygen because there is no
oxygen to speak of, in the vicinity of the filament.


I did not note any reference to " metal oxide layer "



So if one modified the surface of the filament so
that it would radiate less IR and more visible light, the light bulb
be more efficient.

Theoretically, I agree. *This isn't what our researchers were doing,
however.


Hmmm. I thought the whole article was about how the researchers were
modifying the surface of the filament.

Dan

--Winston

--

We now return you to the economic collapse, already in progress.

wrote:
On Jun 5, 3:03 am, Winston wrote:

I respectfully disagree.
Our researchers cleverly implied that
changing the thickness of a metal oxide layer (and the resulting
emissivity changes) had something to do with the changes
in the light bulb but the two effects are quite different and
have nothing to do with each other, IMHO.

The filament is in a vacuum. Heating it does not cause it's
surface to mix more readily with oxygen because there is no
oxygen to speak of, in the vicinity of the filament.


I did not note any reference to " metal oxide layer "

The article cleverly melded two *different* physical changes
together, making it appear as if they were the same.

The article mentions the use of the laser to change the color
of metal ala:

http://machinedesign.com/article/mas...ic-colors-1211

That is a heat process. The source doesn't need to be a femtosecond
laser. You can use any sufficient source of high quality heat
(and oxygen) to do that. We've all seen it as HAZ discoloration:
http://commons.wikimedia.org/wiki/Fi...d_with_HAZ.jpg

So if one modified the surface of the filament so
that it would radiate less IR and more visible light, the light bulb
be more efficient.
Theoretically, I agree. This isn't what our researchers were doing,
however.


Hmmm. I thought the whole article was about how the researchers were
modifying the surface of the filament.

Yup. That was the clever part. You and the U.S. Air Force Office of
Scientific Research were prompted to assume that the two different
physical changes were directly related.

"In 2008, his team used a similar process to
change the color of nearly any metal to blue, golden, and gray, in
addition to the black he'd already accomplished."

[Please refer again to the HAZ photo link. What colors do you see?
I see gray, blue, and golden starting from the most heated area
to the least heated area of the HAZ.]

Here is a smoking gun:
"Guo and Vorobeyv used that knowledge of how to control the size and
shape of the nanostructures—and thus what colors of light those
structures absorb and radiate—to change the amount of each wavelength
of light the tungsten filament radiates."

What was this 'similar process'? I'll bet you a dollar that it was
localized heating of a metal sample to grow a color-reflective
oxide layer. How is that related to the process of vaporizing a tiny
chunk out of a tungsten filament?

My point is that there is no relationship between these two
concepts other than one can use heat in specific forms
to accomplish them.

--Winston



--

We now return you to the economic collapse, already in progress.

On Fri, 05 Jun 2009 08:04:12 -0700, Winston wrote:


What was this 'similar process'? I'll bet you a dollar that it was
localized heating of a metal sample to grow a color-reflective
oxide layer. How is that related to the process of vaporizing a tiny
chunk out of a tungsten filament?

My point is that there is no relationship between these two
concepts other than one can use heat in specific forms
to accomplish them.

--Winston

Your arguments appear to be approaching blind denial of the claimed effect.

Have a look at a butterfly wing under an electron microscope and you'll get a
better idea of what's going on.


Mark Rand
RTFM

Mark Rand wrote:
On Fri, 05 Jun 2009 08:04:12 -0700, Winston wrote:


What was this 'similar process'? I'll bet you a dollar that it was
localized heating of a metal sample to grow a color-reflective
oxide layer. How is that related to the process of vaporizing a tiny
chunk out of a tungsten filament?

My point is that there is no relationship between these two
concepts other than one can use heat in specific forms
to accomplish them.

--Winston

Your arguments appear to be approaching blind denial of the claimed effect.

I prefer to think of it as 'informed denial of the claimed effect'.

What claim do I deny?

The claim, IIRC is that one can make a light bulb universally 'better'
by exposing it's filament to laser light, because the resulting roughened
surface somehow causes it to convert electrical power into visible -
frequency photon emission more efficiently than does the smoother
un-modified filament, without any change in the cross sectional area
of the filament anywhere along it's length.

I don't deny that you can shift the average color temperature of the bulb
upwards towards blue without increased bulb power by thinning the filament,
but I do deny that the effect is produced by anything other than
merely thinning the filament.

I also deny that laser beam exposure 'improves' the bulb because it will
significantly decrease the amount of time that the lamp remains functional
as compared to it's lifetime had it not been exposed.

A bulb design that fails significantly more often than average is not a
better design. It is a worse design even if it is more efficient during
it's short stay in the socket.

Have a look at a butterfly wing under an electron microscope and you'll get a
better idea of what's going on.

Iridescence?
http://en.wikipedia.org/wiki/Iridescent

Can you help me understand your point, please?

Are you saying that the iridescent surface of soap bubbles, butterfly wings
and the inside of abalone shells make them more intense visible light
sources than river rocks, blades of grass or concrete slabs for example?

I deny that, too.

--Winston


--

We now return you to the economic collapse, already in progress.

On Thu, 04 Jun 2009 18:53:23 -0700, Winston
wrote:

Ned Simmons wrote:
On Wed, 03 Jun 2009 20:49:44 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."
Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

As I said above, if the experiment created a hot spot by thinning the
filament the resistance of the filament, and the power consumed, would
change. The experimenters reported there was *no change* in the power
consumption.

In *net* consumption, no change was detected. I get that.
I hypothesize that the local power consumption at the thinned area of the
filament did increase, because it's increased resistance dropped more voltage
across the thinned area for a given amount of current. The increased resistance
of the filament as a whole would have decreased the filament current a tiny
amount, cancelling the effect of the local power consumption increase.

Model it as two PTC resistors in series, one of which is about a percent of the
value of the second one. Triple the value of the smaller resistance and it's
power consumption triples. The net resistance of the network as a whole is
decreased by a couple percent, causing the second resistor to decrease in value.
As a result, current increases once again and a new equilbrium is established
which is very close, if not identical to the pre-modification current.

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it. It's also very
easy to test, so I did, and it just ain't so. Even using a 3-1/2 digit
meter it was easy to observe the current thru a 75W bulb change with
1% changes in applied voltage. The effects of the temperature on the
resistance were clearly apparent, but did not entirely compensate for
increasing voltage.

V I calculated R
119.9 588 203.9
120.8 590 204.7
121.8 592 205.7
122.4 594 206.1

The bulb lifetime is significantly decreased but the study did not encompass
bulb lifetime, just hotspots and spectral shift.

The relationship between power density, temperature, efficiency and
life is well understood -- you can find it in old texts that date back
to the early days of electric lighting. It's hard to believe that
these guys, whose previous work involved fiddling with the emissivity
of metals, are unaware of that relationship and have misinterpreted
the results of their experiment.

They didn't misinterpret, as far as I can see.
They didn't say a word about the post-modification reliability of the bulb.
You could argue that they committed an error of omission about that, if you
were feeling very charitable.

Then I'm not sure what you're claiming. That the researchers have
convinced their peers at a major research university, the Air Force
Office of Scientific Research, and the referees at Physical Review
Letters, but not you, that blasting material off a filament with a
laser is a significant achievement?

--
Ned Simmons

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.

Your model shows a net reduction of voltage available to the bulb.
In the experimenter's case, the amount of voltage to the bulb remained
the same but it was distributed differently in the filament eg. a 'hot spot'
area dissipating significantly more power than it had before it was thinned.

I said that the positive temperature coefficient of the filament would tend
to limit the change of the current through the bulb as the power distribution
in the bulb was changed by thinning some portion of the filament.

Your numbers show that the variation in current through your bulb was
about half the variation in voltage across the bulb. A one volt change
across the bulb caused a 2 milliamp change in current. This is the
nonlinear positive temperature coefficient variation I was on about.

Had that PTC effect not been in place, we would expect to see a 5 milliamp
change in current for a 1 volt change. A new current equilibrium was
established that was within 0.35% of the pre-modification current, under
a voltage change of 0.82%.

(...)

Then I'm not sure what you're claiming.

I'm not claiming much of anything.

Their claim, IIRC is that one can make a light bulb universally 'better'
by exposing it's filament to laser light, because the resulting roughened
surface somehow causes it to convert electrical power into visible -
frequency photon emission more efficiently than does the smoother
un-modified filament, without changing the cross sectional area
of the filament anywhere along it's length.

I don't deny that you can shift the average color temperature of the bulb
upwards towards blue without increased bulb power by thinning the filament,
but I do deny that the effect is produced by anything other than
merely thinning the filament.

I also deny that laser beam exposure 'improves' the bulb because it will
significantly decrease the amount of time that the lamp remains functional
as compared to it's lifetime had it not been exposed.

A bulb design that fails significantly more often than average is not a
better design. It is a worse design even if it is more efficient during
it's short stay in the socket.

That the researchers have
convinced their peers at a major research university, the Air Force
Office of Scientific Research, and the referees at Physical Review
Letters, but not you, that blasting material off a filament with a
laser is a significant achievement?

Blasting material off a filament is a parlor trick, not a significant
achievement.

I believe Mr. Guo and Mr. Vorobeyv are mistaken at best.

--Winston

--

We now return you to the economic collapse, already in progress.

On Fri, 05 Jun 2009 13:01:16 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.

Your model shows a net reduction of voltage available to the bulb.

Not my model. It's the one you proposed in your previous post ("Model
it as two PTC resistors in series, one of which is about a percent of
the value of the second one"), except I moved one resistance outside
the lamp's envelope and turned a knob rather than tweaking it with a
laser.

In the experimenter's case, the amount of voltage to the bulb remained
the same but it was distributed differently in the filament eg. a 'hot spot'
area dissipating significantly more power than it had before it was thinned.

And in my experiment, the voltage across the two resistors was also
constant.


I said that the positive temperature coefficient of the filament would tend
to limit the change of the current through the bulb as the power distribution
in the bulb was changed by thinning some portion of the filament.

What you said (in order to explain the experimenters' observation that
no change in power accompanied the increase in light output) was that
the PTC of the untreated section of the filament would cause the
current to restabilize at a point "very close, if not identical to the
pre-modification current." For that to happen, the current passing
thru the untreated filament must be independent of the applied
voltage, and that's clearly not the case.


Your numbers show that the variation in current through your bulb was
about half the variation in voltage across the bulb. A one volt change
across the bulb caused a 2 milliamp change in current. This is the
nonlinear positive temperature coefficient variation I was on about.

Had that PTC effect not been in place, we would expect to see a 5 milliamp
change in current for a 1 volt change. A new current equilibrium was
established that was within 0.35% of the pre-modification current, under
a voltage change of 0.82%.

Exactly. If treating a spot on the filament changed its resistance (as
I changed the resistance in series with my filament), the resistance
of the adjacent untreated filament would change in the opposite
direction, but the magnitude of change would be smaller. In other
words, there'd be a net change in the lamp's resistance, which would
show up as a change in power.

--
Ned Simmons

Ned Simmons wrote:
On Fri, 05 Jun 2009 13:01:16 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.
Your model shows a net reduction of voltage available to the bulb.

Not my model. It's the one you proposed in your previous post ("Model
it as two PTC resistors in series, one of which is about a percent of
the value of the second one"), except I moved one resistance outside
the lamp's envelope and turned a knob rather than tweaking it with a
laser.

But first, you changed R1 to a linear resistance.
After thinning, it dissipates much more power than it had before.

As power across R1 increases, it's resistance increases nonlinearly.
As power across R2 decreases, it's resistance decreases nonlinearly.

I'm not going to do the arithmetic, but it's a PTC series circuit with a
constant voltage across it. Is it plausible that net power dissipated
by this network remains fairly constant despite the fact that the
ratio of power dissipated by R1 is inversely proportional to the power
dissipated by R2 over a range of say 3% of P2? I think so.

(...)

Exactly. If treating a spot on the filament changed its resistance (as
I changed the resistance in series with my filament), the resistance
of the adjacent untreated filament would change in the opposite
direction, but the magnitude of change would be smaller. In other
words, there'd be a net change in the lamp's resistance, which would
show up as a change in power.

I ain't so sure. My cheapo SPICE simulator does not have a PTC
thermistor component, else I would ask the computer for an answer.

--Winston

--

We now return you to the economic collapse, already in progress.

On Fri, 05 Jun 2009 16:00:04 -0700, Winston
wrote:

Ned Simmons wrote:
On Fri, 05 Jun 2009 13:01:16 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.
Your model shows a net reduction of voltage available to the bulb.

Not my model. It's the one you proposed in your previous post ("Model
it as two PTC resistors in series, one of which is about a percent of
the value of the second one"), except I moved one resistance outside
the lamp's envelope and turned a knob rather than tweaking it with a
laser.

But first, you changed R1 to a linear resistance.

But the voltmeter was connected only across the lamp, the point being
to determine how an unmodified filament behaves when the voltage
across it varies in small increments. And for that purpose, as long as
the measurements are taken at equilibrium, it doesn't matter whether
R1 is temperature dependent or not.

So we know that small changes in the voltage across a lamp result in
proportionally smaller, but measurable, changes in current. Now
replace R1 (my variable resistor) with a second lamp. Apply the
appropriate voltage to the string and note the current. Thin the
filament in the second lamp with a laser, or a genie with an angle
grinder. As we agreed before, the network will reach a new
equilibrium, with the voltage divided according to the new ratio of
the filament resistances, such that the voltage across the unmolested
lamp is slightly higher than it was before. Consequently, the current
in the circuit will have increased a small, but detectable amount, and
so has the sum of the power consumed by the two lamps.

Which is contrary to what was reported in the article. In other words,
a localized thinning of the filament can't explain an increase in
brightness without an increase in power.

--
Ned Simmons

Ned Simmons wrote:
On Fri, 05 Jun 2009 16:00:04 -0700, Winston
wrote:

Ned Simmons wrote:
On Fri, 05 Jun 2009 13:01:16 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.
Your model shows a net reduction of voltage available to the bulb.
Not my model. It's the one you proposed in your previous post ("Model
it as two PTC resistors in series, one of which is about a percent of
the value of the second one"), except I moved one resistance outside
the lamp's envelope and turned a knob rather than tweaking it with a
laser.
But first, you changed R1 to a linear resistance.

But the voltmeter was connected only across the lamp, the point being
to determine how an unmodified filament behaves when the voltage
across it varies in small increments.

The point remains that:

1) Mr. Guo and Mr. Vorobeyv's claim that they 'improved' a light bulb
by subjecting it to laser light does not pass muster.

2) Their explanation that the laser improved lamp efficiency by
creating surface features (independent of a reduction in filament
cross sectional area) is far less likely than a simple reduction
in the cross sectional area of the filament, causing a hot spot.

3) Thinning of the filament will produce:
A) Some aggregate spectral shift towards the blue in the hot spot.
B) Increased power dissipation in the thinned area.
C) Decreased power dissipation in the unmolested area.
D) A reproducible decrease in the life of any lamp thus modified.

We can worry this subject to death, but let's please not lose sight
of the fact that Mr. Guo and Mr. Vorobeyv have apparently made a
technical boo - boo.

And for that purpose, as long as
the measurements are taken at equilibrium, it doesn't matter whether
R1 is temperature dependent or not.

It matters bigtime. We should not draw a conclusion based on a
circuit in a given state of equilibrium and apply it to a
different circuit in a different state of equilibrium.

So we know that small changes in the voltage across a lamp result in
proportionally smaller, but measurable, changes in current. Now
replace R1 (my variable resistor) with a second lamp. Apply the
appropriate voltage to the string and note the current. Thin the
filament in the second lamp with a laser, or a genie with an angle
grinder. As we agreed before, the network will reach a new
equilibrium, with the voltage divided according to the new ratio of
the filament resistances, such that the voltage across the unmolested
lamp is slightly higher than it was before.

Slightly lower, yes? The resistance of the thinned portion of the
filament will increase, causing more voltage to be dropped across
it rather than the unmolested length of the filament. Power shifts.

Consequently, the current
in the circuit will have increased a small, but detectable amount, and
so has the sum of the power consumed by the two lamps.

Which is contrary to what was reported in the article. In other words,
a localized thinning of the filament can't explain an increase in
brightness without an increase in power.

I disagree. Power shifts away from the unmolested portion of the
filament to the thinned portion of the filament.

Is this fun or what?

--Winston


--

We now return you to the economic collapse, already in progress.

Ned Simmons wrote:
On Thu, 04 Jun 2009 18:53:23 -0700, Winston
wrote:

Ned Simmons wrote:
On Wed, 03 Jun 2009 20:49:44 -0700, Winston
wrote:

Ned Simmons wrote:

(...)

If the filament has a thin section the power density at that spot will
indeed be higher, but the overall consumption of the lamp will be
lower. (P=V^2/R) The article says, "... we could actually see this one
patch was clearly brighter than the rest of the filament, but there
was no change in the bulb's energy usage."
Yes, but bulb life is significantly reduced.

Can we really call it a "better light bulb" if we have to replace it
~twice as often? (I don't think so.)

http://en.wikipedia.org/wiki/Incande...b#cite_note-24

"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
which ends in the familiar tiny gap in an otherwise healthy-looking filament."

As I said above, if the experiment created a hot spot by thinning the
filament the resistance of the filament, and the power consumed, would
change. The experimenters reported there was *no change* in the power
consumption.

In *net* consumption, no change was detected. I get that.
I hypothesize that the local power consumption at the thinned area of the
filament did increase, because it's increased resistance dropped more voltage
across the thinned area for a given amount of current. The increased resistance
of the filament as a whole would have decreased the filament current a tiny
amount, cancelling the effect of the local power consumption increase.

Model it as two PTC resistors in series, one of which is about a percent of the
value of the second one. Triple the value of the smaller resistance and it's
power consumption triples. The net resistance of the network as a whole is
decreased by a couple percent, causing the second resistor to decrease in value.
As a result, current increases once again and a new equilbrium is established
which is very close, if not identical to the pre-modification current.

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it. It's also very
easy to test, so I did, and it just ain't so. Even using a 3-1/2 digit
meter it was easy to observe the current thru a 75W bulb change with
1% changes in applied voltage. The effects of the temperature on the
resistance were clearly apparent, but did not entirely compensate for
increasing voltage.

V I calculated R
119.9 588 203.9
120.8 590 204.7
121.8 592 205.7
122.4 594 206.1

The bulb lifetime is significantly decreased but the study did not encompass
bulb lifetime, just hotspots and spectral shift.

The relationship between power density, temperature, efficiency and
life is well understood -- you can find it in old texts that date back
to the early days of electric lighting. It's hard to believe that
these guys, whose previous work involved fiddling with the emissivity
of metals, are unaware of that relationship and have misinterpreted
the results of their experiment.

They didn't misinterpret, as far as I can see.
They didn't say a word about the post-modification reliability of the bulb.
You could argue that they committed an error of omission about that, if you
were feeling very charitable.

Then I'm not sure what you're claiming. That the researchers have
convinced their peers at a major research university, the Air Force
Office of Scientific Research, and the referees at Physical Review
Letters, but not you, that blasting material off a filament with a
laser is a significant achievement?

none of listed places have any relevance to light bulbs in any way at all.