Light Bulb Back Radiation Experiment
Guest essay by Curt Wilson
In the climate blogosphere, there have been several posts recently on the basic principles of radiative physics and how they relate to heat transfer. (see yesterday’s experiment by Anthony here) These have spawned incredibly lengthy streams of arguments in the comments between those who subscribe to the mainstream, or textbook view of radiative heat transfer, and those, notably the “Skydragon Slayers” who reject this view.
A typical statement from a Slayer is that if “you have initially a body kept at a certain temperature by its internal source of energy”, that if another body at a lower temperature is placed near to it, that the radiation from this colder body could not increase the temperature of the warmer body, this being a violation of the 2nd Law of Thermodynamics. They continue that if this were possible, both objects would continually increase the other’s temperature indefinitely, which would be an obvious violation of the 1st Law of Thermodynamics (energy conservation).
This is part of a more general claim by Slayers that radiation from a colder body cannot transfer any energy to a warm body and lead to a higher temperature of the warm body than would be the case without the presence of the colder body.
It occurred to me that these claims were amenable to simple laboratory experiments that I had the resources to perform. A light bulb is a classic example of a body with an internal source of energy. Several Slayers specifically used the example of reflection back to a light bulb as such an example.
In our laboratory, we often have to do thermal testing of our electronic products so we can ensure their reliability. Particularly when it comes to power electronics, we must consider the conductive, convective, and radiative heat transfer mechanisms by which heat can be removed from these bodies with an “internal source of energy”. We have invested in good thermocouple measurement devices, regularly calibrated by a professional service, to make the temperature measurements we need.
We often use banks of light bulbs as resistive loads in the testing of our power electronics, because it is a simple and inexpensive means to load the system and dissipate the power, and it is immediately obvious in at least a qualitative sense from looking at the bulbs whether they are dissipating power. So our lab bench already had these ready.
If you want to isolate the radiative effects, the ideal setup would be to perform experiments in a vacuum to eliminate the conductive/convective losses. However, the next best thing is to reduce and control these to keep them as much alike as possible in the different phases of the experiment.
So, on to the experiment. This first picture shows a standard 40-watt incandescent light bulb without power applied. The lead of the thermocouple measuring device is taped to the glass surface of the bulb with heat-resistant tape made for this purpose. The meter registers 23.2C. In addition, a professional-grade infrared thermometer is aimed at the bulb, showing a temperature of 72F. (I could not get it to change the units of the display to Celsius.) Note that throughout the experiment, the thermocouple measurements are the key ones.
Next, the standard North American voltage of 120 volts AC (measured as 120.2V) was applied to the bulb, which was standing in free air on a table top. The system was allowed to come to a new thermal equilibrium. At this new equilibrium, the thermocouple registered 93.5C. (The IR thermometer showed a somewhat lower 177F, but remember that its reported temperature makes assumptions about the emissivity of the object.)
Next, a clear cubic glass container about 150mm (6”) on a side, initially at the room temperature of 23 C, was placed over the bulb, and once again the system was allowed to reach a new thermal equilibrium. In this state, the thermocouple on the temperature of the bulb registers 105.5C, and the outer surface of the glass container registers 37.0C (equivalent to body temperature).
The glass container permits the large majority of the radiative energy to escape, both in the visible portion of the spectrum (obviously) and in the near infrared, as standard glass is highly transparent to wavelengths as long as 2500 nanometers (2.5 microns). However, it does inhibit the direct free convection losses, as air heated by the bulb can only rise as far as the top of the glass container. From there, it must conductively transfer to the glass, where it is conducted through the thickness of the glass, and the outside surface of the glass can transfer heat to the outside ambient atmosphere, where it can be convected away.
The next step in the experiment was to wrap an aluminum foil shell around the glass container. This shell would not permit any of the radiative energy from the bulb to pass through, and would reflect the large majority of that energy back to the inside. Once again the system was allowed to reach thermal equilibrium. In this new state, the thermocouple on the surface of the bulb registered 137.7C, and the thermocouple on the outer surface of the glass registered 69.6C. The infrared thermometer is not of much use here due to the very low emissivity (aka high reflectivity) of the foil. Interestingly, it did show higher temperatures when focused on the tape on the outside of the foil than on the foil itself.
Since adding the foil shell outside the glass container could be reducing the conductive/convective losses as well as the radiative losses, the shell was removed and the system with the glass container only was allowed to re-equilibrate at the conditions of the previous step. Then the glass container was quickly removed and the foil shell put in its place. After waiting for thermal equilibrium, the thermocouple on the surface of the bulb registered 148.2C and the thermocouple on the outside of the foil registered 46.5C. The transient response (not shown) was very interesting: the temperature increase of the bulb was much faster in this case than in the case of adding the foil shell to the outside of the glass container. Note also how low the infrared thermometer reads (84F = 29C) on the low-emissivity foil.
Further variations were then tried. A foil shell was placed inside the same glass container and the system allowed to reach equilibrium. The thermocouple on the surface of the bulb registered 177.3C, the thermocouple on the outer surface of the foil registered 67.6C, and the infrared thermometer reading the outside of the glass (which has high emissivity to the wavelengths of ambient thermal radiation) reads 105F (40.6C).
Then the glass container was removed from over the foil shell and the system permitted to reach equilibrium again. The thermocouple on the surface of the bulb registered 176.3C and the thermocouple on the outside of the foil registered 50.3C.
All of the above examples used the reflected shortwave radiation from the aluminum foil. What about absorbed and re-emitted longwave radiation? To test this, a shell of black-anodized aluminum plate, 1.5mm thick, was made, of the same size as the smaller foil shell. A black-anodized surface has almost unity absorption and emissivity, both in the shortwave (visible and near infrared) and longwave (far infrared). Placing this over the bulb (without the glass container), at equilibrium, the thermocouple on the bulb registered 129.1C and the thermocouple on the outside of the black shell registered 47.0C. The infrared thermometer read 122F (50C) on the tape on the outside of the shell.
The power source for this experiment was the electrical input. The wall voltage from the electrical grid was steady at 120.2 volts. The electrical current was measured under several conditions with a professional-grade clip-on current sensor. With the bulb in open air and a surface temperature of 96.0C, the bulb used 289.4 milli-amperes of current.
With the bulb covered by a foil shell alone and a surface temperature of 158.6C, the bulb drew slightly less, 288.7 milliamperes.
Summary of Results
The following table shows the temperatures at equilibrium for each of the test conditions:
| Condition | Bulb Surface Temperature | Shell Temperature |
| Bulb open to room ambient | 95C | — |
| Bulb covered by glass container alone | 105C | 37C |
| Bulb covered by glass container and outer reflective foil shell | 138C | 70C (glass) |
| Bulb covered by outer reflective foil shell alone | 148C | 46C (foil) |
| Bulb covered by inner reflective foil shell inside glass container | 177C | 68C (foil) |
| Bulb covered by inner reflective foil shell alone | 176C | 50C |
| Bulb covered by black-anodized aluminum shell alone | 129C | 47C |
Analysis
Having multiple configurations permits us to make interesting and informative comparisons. In all cases, there is about a 35-watt (120V x 0.289A) electrical input to the system, and thermal equilibrium is reached when the system is dissipating 35 watts to the room as well.
I used a low-wattage (40W nominal) bulb because I had high confidence that it could take significant temperature increases without failure, as it has the same package design as much higher-wattage bulbs. Also, I would not be working with contraband high-wattage devices 😉
The case with the glass container alone is the important reference case. The glass lets virtually all of the radiant energy through, while inhibiting direct convection to the room ambient temperature of 23C. Conductive/convective losses must pass from the surface of the bulb, through the air under the container, to and through the glass, and then to the room atmosphere, where it is conducted/convected away. Under these conditions, the bulb surface temperature is 105C, which is 10C greater than when the bulb can conductively dissipate heat directly to the room atmosphere.
Compare this case to the case of the larger foil shell alone. The foil shell also inhibits direct conductive/convective losses to the room atmosphere, but it will not inhibit them to any greater extent. In fact, there are three reasons why it will inhibit these losses less than the glass container will. First, the material thermal conductivity of aluminum metal is far higher than that of glass, over 200 times greater (>200 W/(m*K) versus <1.0 W/(m*K)). Second, the foil, which is a small fraction of a millimeter thick, is far thinner than the glass container, which is about 4 mm thick on average. And third, the surface area of the foil is somewhat larger than the glass container, so it has more ability to conductively transfer heat to the outside air.
And yet, the surface of the bulb equilibrated at 146C under these conditions, over 40C hotter than with the glass container. With conductive/convective losses no less than with the glass container, and very probably greater, the only explanation for the higher temperature can be a difference in the radiative transfer. The glass container lets the large majority of the radiation from the bulb through, and the foil lets virtually none of it through, reflecting it back toward the bulb. The presence of the foil, which started at the room ambient of 23C and equilibrated at 46C, increased the temperature of the bulb, which started at 105C on the outside (and obviously warmer inside). The reflected radiation increased the temperature of the bulb, but did not produce “endless warming”, instead simply until the other losses that increase with temperature matched the input power of 35 watts.
Interestingly, the foil shell without the glass container inside led to a higher bulb temperature (148C) than the foil shell with the glass container inside (138C). Two layers of material around the bulb must reduce conductive/convective losses more than only one of them would, so the higher temperature must result from significantly more reflected radiation back to the bulb. With the glass inside, the reflected radiation must pass through two surfaces of the glass on the way back to the bulb, neither of which passes 100% through.
Another interesting comparison is the large foil shell that could fit outside of the glass container, about 160mm on a side, with the small foil shell that could fit inside the glass container, about 140mm on a side. With the large shell alone, the bulb temperature steadied at 148C; with the smaller shell, it steadied at 176C. With all direct radiative losses suppressed in both cases, the difference must come from the reduced surface area of the smaller shell, which lessens its conductive/convective transfer to the outside air at a given temperature difference. This is why halogen incandescent light bulbs, which are designed to run hotter than standard incandescent bulbs, are so much smaller for the same power level – they need to reduce conductive/convective losses to get the higher temperatures.
All of the above-discussed setups used directly reflected radiation from the aluminum foil. What happens when there is a barrier that absorbs this “shortwave” radiation and re-emits it as “longwave” radiation in the far infrared? Can this lead to higher temperatures of the warmer body? I could test this using black-anodized aluminum plate. Black anodizing a metal surface makes it very close to the perfect “blackbody” in the visible, near-infrared, and far-infrared ranges, with absorptivity/emissivity (which are the same at any given wavelength) around 97-98% in all of these ranges.
With a black plate shell of the same size as the smaller foil shell, the bulb surface temperature equilibrated at 129C, 24C hotter than with the glass container alone. Once again, the thin metal shell would inhibit conductive/convective losses no better, and likely worse than the glass container (because of higher material conductivity and lower thickness), so the difference must be from the radiative exchange. The presence of the shell, which started at the room ambient of 23C and increased to 47C, caused the bulb surface temperature to increase from 105C to 129C.
Another interesting comparison is that of the smaller foil shell, which led to a bulb surface temperature of 176C and a shell temperature of 50C, to the black plate shell of the same size, which led to a bulb surface temperature of 129C and a shell temperature of 46C. While both of these create significantly higher bulb temperatures than the glass container, the reflective foil leads to a bulb surface temperature almost 50C higher than the black plate does. Why is this?
Consider the outside surface of the shell. The foil, which is an almost perfect reflector, has virtually zero radiative absorptivity, and therefore virtually zero radiative emissivity. So it can only transfer heat to the external room by conduction to the air, and subsequent convection away. The black plate, on the other hand, is virtually the perfect absorber and therefore radiator, so it can dissipate a lot of power to the room radiatively as well as conductively/convectively. Remember that, since it is radiating as a function of its own temperature, it will be radiating essentially equally from both sides, there being almost no temperature difference across the thickness of the plate. (Many faulty analyses miss this.) The foil simply reflects the bulb’s radiation back to the inside and radiates almost nothing to the outside. This is why the infrared thermometer does not read the temperature of the foil well.
The electrical voltage and current measurements were made to confirm that the increased temperature did not come from a higher electrical power input. The current measurements shown above demonstrate that the current draw of the bulb was no higher when the bulb temperature was higher, and was in fact slightly lower. This is to be expected, since the resistivity of the tungsten in the filament, as with any metal, increases with temperature. If you measure the resistance of an incandescent bulb at room temperature, this resistance is less than 10% of the resistance at its operating temperature. In this case, the “cold” resistance of the bulb is about 30 ohms, and the operating resistance is about 415 ohms.
Let’s look at the dynamic case, starting with the thermal equilibrium under the glass container alone. 35 watts are coming into the bulb from the electrical system, and 35 watts are leaving the bulb through conductive losses to the air and radiative losses to the room through the glass. Now we replace the glass with one of the metal shells. Conductive losses are not decreased (and may well be increased). But now the bulb is receiving radiant power from the metal shell, whether reflected in one case, or absorbed and re-radiated back at longer wavelengths in the other. Now the power into the bulb exceeds the power out, so the temperature starts to increase. (If you want to think in terms of net radiative exchange between the bulb and the shell, this net radiative output from the bulb decreases, and you get the same power imbalance.)
As the temperature of the bulb increases, both the conductive losses to the air at the surface of the bulb increase (approximately proportional to the temperature increase) and the radiative losses increase as well (approximately proportional to the 4th power of the temperature increase). Eventually, these losses increase to where the losses once again match the input power, and a new, higher-temperature thermal equilibrium is reached.
I originally did these tests employing a cylindrical glass container 150mm in diameter and 150mm high with and without foil shells, and got comparable results. In the second round shown here, I changed to a cubic container, so I could also create a black-plate shell of the same shape.
It is certainly possible that improvements to these experiments could result in differences of 1 or 2C in the results, but I don’t see any way that they could wipe out the gross effect of the warming from the “back radiation”, which are several tens of degrees C.
All of these results are completely in line with the principles taught in undergraduate engineering thermodynamics and heat transfer courses. The idea that you could inhibit net thermal losses from an object with an internal power source, whether by conductive, convective, or radiative means, without increasing the temperature of that object, would be considered ludicrous in any of these courses. As the engineers and physicists in my group came by the lab bench to see what I was up to, not a single one thought for a moment that this back radiation would not increase the temperature of the bulb.
Generations of engineers have been taught in these principles of thermal analysis, and have gone on to design crucial devices and infrastructure using these principles. If you think all of this is fundamentally wrong, you should not be spending your time arguing on blogs; you should be out doing whatever it takes to shut down all of the erroneously designed, and therefore dangerous, industrial systems that use high temperatures.
Conclusions
This experiment permitted the examination of various radiative transfer setups while controlling for conductive/convective losses from the bulb. While conductive/convective losses were not eliminated, they were at least as great, and probably greater, in the cases where a metal shell replaced the glass shell over the bulb.
Yet the bulb surface temperature was significantly higher with each of the metal shells than with the glass shell. The only explanation can therefore be the radiative transfer from the shells back to the bulb. In both cases, the shells were significantly cooler than the bulb throughout the entire experiment, both in the transient and equilibrium conditions.
We therefore have solid experimental evidence that radiation from a cooler object (the shell) can increase the temperature of a warmer object (the bulb) with other possible effects well controlled for. This is true both for reflected radiation of the same wavelengths the warmer body emitted, and for absorbed and re-radiated emissions of longer wavelengths. The temperature effects are so large that they cannot be explained by minor setup effects.
Electrical measurements were made to confirm that there was not increased electrical power into the bulb when it was at higher temperatures. In fact, the electrical power input was slightly reduced at higher temperatures.
This experiment is therefore compatible with the standard radiative physics paradigm that warmer and cooler bodies can exchange radiative power (but the warmer body will always transfer more power to the cooler body). It is not compatible with the idea that cooler bodies cannot transfer any power by radiative means to warmer bodies and cause an increase in temperature of the warmer body.
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UPDATE: The Principia/Slayers group has post a hilarious rebuttal here:
http://principia-scientific.org/supportnews/latest-news/210-why-did-anthony-watts-pull-a-bait-and-switch.html
Per my suggestion, they have also enabled comments. You can go discuss it all there. – Anthony
Myrrh, I think part of the problem with your posts is that you do not understand what “Thermal Radiation” is. You seem to think that it means “radiation which heats the target”. It does not mean that. It means radiation whose characteristics depend on the temperature of the source. The visible light from the sun is thermal radiation.
I would hope no one was thinking reflection is the same as absorption/emission, as it is worked out before you deal with the energy actually absorbed by a surface, last time I checked.
Gary Hladik says (May 29, 2013 at 4:01 pm ): “Greg House says (May 29, 2013 at 3:04 pm): “What the manufacturer has written about back/reflected radiation warming the source has no basis in science.” *sigh* Here we go again. I supplied …Greg–with a scientific reference in the thread to Part 1: http://www.osti.gov/bridge/servlets/purl/5269770/5269770.pdf
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There is nothing in the document about reflective coating increasing the temperature of the filament.
Exactly as I said before, a brighter spot can still be achieved by a reflector. So, here we go again: back radiation warming effect on the source still has no basis in science.
Greg Mansion, you say, “your numbers are not realistic, specifically the 105C for “Bulb covered by glass container alone”. This alone renders your conclusions invalid.”
I assure you, my numbers are very realistic, taken by professional-grade instrumentation that is regularly calibrated by an outside service, suitable for ISO-9000 quality audits, and traceable back to National Institutes of Standards and Technology (NIST) references.
Your confusion stems from the fact that you have absolutely no real-world sense of how physical systems actually work. With regard to Anthony’s experiment, the idea that a horizontally offset plane would have any noticeable effect on vertical convection removing heat from the bulb is absurd. Without any full obstruction above, and over half of the 360-degree span below the bulb to supply replacement air, I don’t even think you could measure the effect of the mirror on convection.
With regard to my experiment, you think that the glass container is not transparent to the infrared that the bulb is putting out. If you had bothered to actually read and comprehend what I had written, you would have noticed that the glass is transparent to the large majority of the (near) infrared that the bulb puts out. (There are many places you can verify this independently.) One of the commenters above talks about the special coating he puts on his windows/skylights to keep this near infrared out. Is he wasting his money?
That’s almost…lyrical. But it’s lyrical-ness is quite irrelevant. The Sun’s surface temperature is NOT “millions of degrees centigrade”, it’s about 6500K, at its “surface”. If it were millions of degrees centigrade, it would be putting out a great deal of its energy as X-rays. Which would be very bad for us indeed.
But that’s beside the main point, which is this: what you said about the Sun radiating is true of literally every other object in the Universe.
But let’s say it’s just true for stars. Let’s take the star Sirius, for example. It’s just sitting there, minding its own business, happily streaming radiation, and radiation from our Sun (which is itself busily streaming out in all directions) strikes it. What happens to that (admittedly very small amount, at that distance) radiation? Does it:
a) Pass right through Sirius as if it wasn’t even there,
b) Reflect off of Sirius as if it were a mirror, or
c) Get absorbed by Sirius, or
d) Other (MUST SPECIFY)
Just a mini-quiz for you. After you’ve answered it, I have an additional question, to wit: Does your answer change if you know that the Sun is cooler than Sirius?
Myrrh says (May 29, 2013 at 6:10 pm): “It’s too bad that you’ve blocked out my explanation that size matters…,”
Hmmm. Words vs experiment…no, sorry, I gotta go with experiment. Cute phrase, though. 🙂
“Do you really want to be stuck in that time warp?”
What time warp? The photos in my link were taken in modern times, and the experiment could be repeated tomorrow. (I’m actually thinking of doing it with my niece; not all hands-on science is so visually appealing to kids). Myrrh, when you look at the photos of the thermometers illuminated by blue, yellow, and infrared light, do you not see the temperature increase in the visible light? If you don’t, you should probably see an optometrist.
If photons cannot travel from a cooler object to a warmer one, then:
1. When the sun is behind my head, what is in front of me is invisible.
2. I cannot see any object cooler than the retina in my eye (glaciers, mountain-tops, ice cream etc).
3. The sun should appear to be covered in black spots due to hotter objects in the universe not allowing radiation in their direction. Since there are no such black spots, the sun must be the hottest object in the universe.
What a strange world the slayers inhabit 🙂
[snip – Greg House under a new fake name. Verified by network path. Mr. House has been shown the door but decided to come back as a fake persona preaching the Slayer/Principia meme. -Anthony]
Next up: the surface of the Earth is the same temperature as its core.
Congratulations and thanks to Curt for designing and methodically carrying out a decisive experiment that demonstrates cooler bodies can actually warm warmer ones through radiative energy transfer. However while its outcome may always have been predictable (and obviously so) for scientifically sophisticated readers (as he reports it was for his colleagues who saw him doing the experiment) its import seems to have failed to communicate to many other readers here as well as to ‘Slayers’ like Joseph Postma. Why should that be?
I think the main reason is possibly that Curt’s experiment was too complex. It’s complexity allows too much ‘wiggle room’ for minds that cannot, or do not want to understand it to misunderstand it and to attribute its results to spurious causes like convection or to obscure the experiment’s significance by burying it in endless quibbles about the minutiae of the energy-transfer processes involved. One might argue (perhaps rightly) that such readers are simply prejudiced or that they are simply ignorant of the relevant laws of physics, but the fact remains that the experiment has failed to overcome whatever prejudices they might have, has failed to enlighten them about the true laws of physics and has communicated its meaning and significance only to those people who already understand those things anyway. In short, it appears just to have preached to the choir.
If we want to settle this dispute with a critically decisive experiment then I think that experiment needs to be extremely simple in its design so that there can be no question of spurious causes and no hidden details for querulous minds to quibble over. How can we design such an experiment?
I think the place to start is with the question that we are wanting the experiment to answer, ie. that of whether or not a cooler body can warm a warmer one through radiative energy transfer. Then our problem becomes one of conceiving a situation that can be created in a laboratory in which two bodies whose temperatures can be measured are able to interact solely by radiative transfer processes. (For all its virtues Curt’s experiment did not do this but tried instead also to accommodate conductive and convective energy transfer processes within the experiment and then sought to neutralise their effects by the appropriate addition and removal of glass and metallic shells. That approach is complicated.)
The requirement that spurious causes be eliminated means that the experiment has to be done in a vacuum. Only this can eliminate the possibility of convective effects. (As Curt said, doing it in air under controlled conditions is ‘the next best thing’. But why can we not go for ‘the best thing’ and do it in a vacuum anyway?)
Furthermore, the possibility of heat transfer between the two bodies by conduction should also be reduced to an absolute minimum. This requires that the two bodies do not come into direct material contact and that any material medium which connects them should be as thermally non-conductive as possible.
There is also another requirement of the experimental set-up, which is that it should mimic the radiative energy transfer process that is hypothesised to occur in the atmospheric greenhouse effect, namely that of radiation absorption and emission by both bodies without any reflection being involved. This constraint requires the two bodies in the experiment to have black, non-reflective surfaces and requires that we not make use of any reflective foils and shells.
Having determined the necessary requirements of the experimental design we can now proceed to envisage a specific experiment that would meet them. At this point it may be most useful if I offer a concrete suggestion.
Suppose we take two identical thin plates with matt-black surfaces and let one plate be capable of being heated by passing an electric current through it. Let us attach temperature-sensors to both plates and let us mount them upright on thermally non-conductive bases on opposite sides of the base of a large bell-jar facing each other. (The various leads that are attached to the two plates should not be attached to their internal faces and should not pass between them either so that the space between them is clear. The leads could pass through appropriate channels in the bell-jar’s base to connect with their respective apparatuses outside.) Let the electrically heatable plate (call it ‘A’) be set in a fixed position on the bell-jar’s base and let the non-heatable plate (call it ‘B’) be set on a moveable plinth that is resting on the bell-jar’s base whereby plate B can be brought horizontally closer to plate A, or further away from it, by turning a knob or handle outside.
Now let the bell-jar be placed over the base with the two plates mounted upon it and let the air under the bell-jar be evacuated. Let the temperature sensors on both plates be connected to their apparatus outside and when their temperatures appear to have stabilised let them be recorded. (The temperatures of A and B should both be equal to the ambient temperature at this stage.)
Next let the electrical power to plate A be switched on and when the temperatures of both plates have stabilised let them be recorded again. We should now find that the temperature of plate A has risen considerably, because it is receiving electrical energy from its power-source and is converting it to thermal energy inside itself before radiating it away to its environment, all at a constant rate. We should also find that the temperature of plate B has also risen slightly though, because it will be absorbing some of the energy radiating from plate A and converting that to thermal energy inside itself before radiating it away to the common environment of both plates A and B likewise. So plate A should stabilise at a substantially higher temperature than plate B and we can now designate plate A our ‘warm body’ and plate B our ‘cool body’. These expectations are not in dispute by the ‘Slayers’.
The expectation that is critically in dispute in this experiment is about what should happen next when we turn the knob or handle that controls the position of the ‘cool body’ plate B and bring it closer to the ‘warm body’ plate A (but not so close that they touch). Apparently the expectation of the ‘Slayers’ is that the temperature of ‘cool body’ plate B should rise (because it is receiving more radiant energy from ‘warm body’ plate A by virtue of being closer to it now) while the temperature of ‘warm body’ plate A should remain exactly the same as it was (because it is not receiving any more energy from anywhere than it was before).
But the expectation of the ‘conventionalists’ (if I may call them that provisionally) is that the temperatures of both plates A and B should increase. In their expectation ‘cool body’ plate B should warm for the same reason that the ‘Slayers’ expect it to warm (ie. because it is receiving more radiant energy from ‘warm body’ plate A), but ‘warm body’ plate A should also warm because it is receiving more radiant energy from ‘cool body’ plate B by virtue of its closer proximity too.
If we run this experiment (or another one very like it) I think we should all be able to see clearly and unequivocally which side in this dispute has the truth of the matter without the need for convoluted theoretical arguments or protracted debates about abstruse technicalities that relatively few people know about or understand. It could finally decide the issue for all but the obdurately-minded once and for all.
Slartibartfast said @ur momisugly May 29, 2013 at 7:12 pm
Which as any fule who listens to Al Gore knows is Millions of degrees :-)))))
Enough with PSI / Slayers mumbo-jumbo, baseless claims, and empty remarks like ” Keep an eye at PSI”.
PSI / Slayers, you made the Light Bulb / Mirror “do not heat” claim and statement, thus the burden of proof is on you. It is not our burden to prove PSI / Slayers claim or statement is wrong (which has been done twice).
PSI / Slayers – Provide an experiment that can be duplicated by people here (easily replicated with minimal cost); which proves your position on Light Bulb / Mirror** and claim that “a light bulb facing a mirror does not heat up”. Provide us with data, calculations, and results; along with images and video taken during your experiment, and list of materials and equipment need to replicate. PSI / Slayers should have no problem doing so, given your comments and remarks here.
**( http://wattsupwiththat.files.wordpress.com/2013/05/psi_siddonscapture.png ).
To save Anthony the headaches of dealing with fallout, post the results on your PSI website and open the post up to external (non PSI member) comments. Be more than prepared to defend your experiment and work within 12 hours of questions/remarks/comments being posted. Any longer attempt to delay, such as “Keep an eye …”; will be deemed admission by PSI / Slayers you can not, and your position / claim is mumbo-jumbo / baseless / nonsense.
The clock is ticking…
Magic Turtle says (May 29, 2013 at 7:15 pm): “If we want to settle this dispute with a critically decisive experiment then I think that experiment needs to be extremely simple in its design so that there can be no question of spurious causes and no hidden details for querulous minds to quibble over. How can we design such an experiment?”
Great minds think alike! You’ve basically described Dr. Spencer’s “Yes, Virginia” thought experiment:
http://www.drroyspencer.com/2010/07/yes-virginia-cooler-objects-can-make-warmer-objects-even-warmer-still/
On a recent thread at Dr. Spencer’s site, “Bill” noted that he has access to a vacuum chamber
http://www.drroyspencer.com/2013/05/a-simple-experiment-to-show-how-cool-objects-can-keep-warm-objects-warmer-still/#comment-80449
so the “Yes, Virginia” experiment may leave the realm of thoughts-only. 🙂
If/when the experiment is run, it would be nice to gather the Pink Unicorn Brigade’s predictions beforehand, just to keep them honest. Now some have boldly predicted it won’t work as advertised (e.g. Pierre LaTour at A-Site-Which-Must-Not-Be-Linked), but others on this board have failed to respond when I’ve asked them for predictions in the past. Perhaps a prediction could be required as a condition of continued commenting privileges on this site. 🙂
Greg House says (May 29, 2013 at 6:42 pm): “There is nothing in the document about reflective coating increasing the temperature of the filament.”
Oh, sorry. I thought you were smart enough to realize that emitting the same visible light meant maintaining the same temperature with lower power input, i.e. the coating raises the filament temp to “normal” despite a lower power input that would otherwise produce a lower filament temp. My bad. If it helps, this reference says it explicitly:
http://www.ies.org/PDF/100Papers/053.pdf
It’s not searchable, so you’ll have to nitpick the old-fashioned way. But quoting from the right side of the front page,
“The basic idea behind the Halogen-IR lamp is to place a spectrally reflecting filter on the outside of a halogen lamp envelope to reflect back a portion of the emitted infrared energy to the filament where a fraction of the reflected energy is absorbed. The absorbed radiation reduces the input electrical power needed to maintain the filament temperature, hence increasing the efficacy.”
You should read the entire paper. It’s fascinating stuff.
“Exactly as I said before, a brighter spot can still be achieved by a reflector.”
Are you really this dense? The reflector encloses the filament, so the “brighter spot” is the filament itself.
Wait, did Greg just admit that a filament’s reflected radiation can make the filament “brighter”??? 🙂
I have no love with the attitude displayed often by Slayers but I feel this is a waste of time and achieves nothing.
Anthony – it is true you are carrying out the experiment to the letter and indeed shows up appropriately.
An experimental physicist would never have prescribed it in that manner. Alan Siddons cocked up badly. The glass bulb is not the issue at all; it is the filament which needs testing. Reflection of light is not reflection of energy from the glass bulb at all.
Such a poorly designed experiment simply gives measures of various insulating or restrictive heat loss methods.
The real issue is whether a spontaneously radiating body can INCREASE its OWN temperature by back radiation or back reflection – in the absence of other constraints. My answer is in the negative and would agree with the Slayers.
This is not simply tested when the convection and conduction is not controllable in this experiment. In fact every effort seems to be made to use it to increase the T – whether it be filament or bulb.
The comment linked does not mention “105C”. In fact, no where on the page is this number mentioned. Can you be more specific?
All of human energy output per year is equal to about 1 hour’s worth of sunlight falling on the surface of the earth.
D. J. Hawkins said @ur momisugly May 29, 2013 at 10:42 pm
The string “105C” occurs a dozen times on this page, including the table in the article that mentions “105C” several times in the text.
I was refering to the “Slayer” page Greg claimed discussed the issue.
I am none to bright, so is the same. I put a pot full of water on a stove, it has no safety valve, the bot of water heats and heats and heats until it explodes.
pot!!
has my stove surface got warmer.
Magic Turtle says:
May 29, 2013 at 7:15 pm
Gary Hladik says:
May 29, 2013 at 8:50 pm
————————————————————–
If you have access to both high torr vacuum pump and peltier cooling chips the experiment build is easy. Build two evacuated test chambers similar to this one –
http://i44.tinypic.com/2n0q72w.jpg
– with internal matt black target plates and external SW illumination. An exploded view of the internals here –
http://i43.tinypic.com/33dwg2g.jpg
– the only difference between the chambers is the matt black foil layer in chamber 1 between the target plate and the -25C base plate. Shown in cut away here –
http://i43.tinypic.com/2wrlris.jpg
It does not effect the experiment that the target plate is illuminated from the “back”. Controlled sources of energy external to the chambers is important.
My prediction* is that the target plate in chamber 1 will reach a higher temperature. The two shell mathematical model works, as will the two shell empirical experiment. The reason that the AGW hypothesis fails is not due to errors in radiative physics but rather fluid dynamics and gas conduction. Because of their critical role in tropospheric convective circulation and emision of IR to space from altitude, radiative gases act to cool our atmosphere at all concentrations above 0.0ppm.
*Prediction? I am of course cheating 😉
PS. Gary, this experiment is small enough to run in a kitchen 😉
Moderators – it would be great if these images could be posted inline.
Greg Mansion says:
May 29, 2013 at 7:11 pm
a) to have presented a false number as the basis for your comparison (much too low temperature despite a very strong reduction of convective cooling) and
b) to have misrepresented the quality of glass of being very much opaque to IR.
Regardless of the discussion, accusing someone for forging the data to prove one’s point needs proof beyond doubt. That simply can be done by repeating the experiment. Which, even without very accurate measurements, can be done at your home.
So, please refrain from such accusations until you have done the test yourself or by one of the other slayers.
Further about b):
From Yaho0!:
There’s near-IR (NIR), which goes from about 800nm to 2500nm. Medium wavelength IR (MWIR), going from 3000 to 5000 nm, and Long wavelength IR (LWIR) going from 8000 to 14000 nm.
NIR is transmitted by almost all silica-based glasses as well as a variety of plastics and polycarbonates. In fact, typical PCs used in sunglasses are actually more transmissive in NIR than the visible.
MWIR can be transmitted by sapphire, diamond, silicon, germanium, zinc selenide, zinc sulfide, magnesium fluoride, and some others I can’t remember
LWIR can be transmitted by germanium, silicon, zinc selenide and some plastics.
In the case of incandescent light, most IR emitted is NIR.
If the (mostly ordinary) glass of the (non-halogen) bulb wasn’t transparant to NIR, it would get extremely hot…
richard says:
May 30, 2013 at 12:10 am
has my stove surface got warmer.
Yes, warmer than without the pot, once it warmed beyond ambient temperature…