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
[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]
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 Sgt. Schult–er, Greg–with a scientific reference in the thread to Part 1:
http://www.osti.gov/bridge/servlets/purl/5269770/5269770.pdf
But no doubt he’ll continue to see nothing. Considering that we’re discussing an efficient incandescent bulb, it’s kind of ironic that he refuses to see the “light”. 🙂
Greg Mansion:
So where’s the circular reasoning? Had you seen a flaw, I would have expected you to list it and explained why it was a flaw (likely gleefully) instead of making a claim to an unspecified error.
Do me the favor of either providing the error you’ve seen that we all have missed, or stop making false claims.
Physics is just physics, it cares not about the political context. The same physics are involved in both cases.
[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]
For the most part, NO, since they are transparent to the most of the wavelengths of the incoming radiation.
[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]
When gaseous CO2 molecules in the air absorb IR photons of the right energy, their electrons gets excited & radiate photons in all directions.
I get that. What I don’t get is why noble gases behave any differently than other gases. Or (I think this addresses your last reply to me more directly): why O2 and N2 behave differently.
Wait, wait…I’ve heard this one before. It starts: “there’s a windmill in my beard”, right?
Myrrh says (May 29, 2013 at 2:46 pm ): “Sadly, real world examples are blocked out of mind.”
It’s too bad that Myrrh can’t appreciate the delicious irony of that statement, having blocked the Herschel experiment out of his own mind. Here’s the backyard version (again), disproving his claim that visible light can’t heat matter:
http://www.ipac.caltech.edu/outreach/Edu/Herschel/backyard.html
Remember the scene in “Galaxy Quest” when Sigourney Weaver asks the aliens, “Is there no one on your planet who behaves in a way that’s contrary to reality?” If Myrrh had been present, everybody would have pointed at him. 🙂
Slartibartfast says:
May 29, 2013 at 4:21 pm
Noble gases like Ar, the one that matters in Earth’s air, & the same-atom molecules N2 & O2, don’t have bonds that absorb IR photons, then do the twist & gyrate. The electrons of chemical compounds like CO2, CH4 & H2O do get high, then come down, emitting photons.
Actually, no electrons get excited. When CO2 molecules are excited by IR, there is a physical vibration. This is important because it makes it possible for the CO2 to lose energy by colliding with other molecules in the atmosphere. That has the effect of reducing the re-radiation at the exciting wavelength. http://www.wag.caltech.edu/home/jang/genchem/infrared.htm
Roger Clague says:
May 29, 2013 at 1:57 pm
***************
Wow, so many misconceptions in a single post. You say, “We are discussing a specific experiment proposed by Slayer Alan Siddons … The claim is not about the temperature of the bulb surface.”
While I never said I was duplicating Siddons’ experiment, and I actually did these experiments before I ever saw that, let’s look at what Siddons said: “A light bulb facing a mirror does not heat up or shine brighter from its own radiation coming back.”
Anthony was obviously testing the “does not heat up” claim, and finding it false. My experiment found it false as well. Neither of tested the brightness claim, nor claimed to have done so.
You also say, “Your electrical measurements show that the bulb did not get brighter, no increase in power consumed ( W = V x A ) and emitted.” You are completely confusing power and brightness here, and there is no simple relationship. There is no conservation of brightness law, as there is for a conservation of energy.
I have in the electronics I design resistors that dissipate this much power that do not run hot enough to produce any visible radiation at all. (I would be in deep, deep trouble if they did…). You could have a resistor dissipating this much power that faintly glow red and put out a lot of infrared, as in a toaster or a heat lamp. In a standard incandescent, these are hot enough to put out about 5% visible and 95% infrared. In a halogen bulb, they are hotter yet, and put out a higher percentage of visible, and with internal reflection of infrared, still hotter and put out more visible light.
There are several things going on here. Conductive/convective losses increase approximately linearly with absolute temperature, while radiative losses increase approximately as the 4th power of absolute temperature. So the hotter the resistor, the higher the percentage of power is radiated away instead of being conducted/convected away (holding total power constant). Also the hotter the resistor, the more the spectrum being radiated moves into the visible range (again holding power constant).
With constant voltage and resistance, and therefore constant power, the higher the temperature, the more total radiation emitted, and the higher the percentage of this radiation in the visible range. Both effects make it “brighter”.
But it gets even further from your analysis. The resistance of metal, like the tungsten filament, increases with higher temperatures, and at constant voltage, this means the current decreases with higher temperatures. My measurements showed a very slight decrease in current. I would have had a better case for increased brightness if my measurements had shown a larger decrease – an increase would have implied lower brightness.
Thanks for the explanation, John. It does make sense that molecules that don’t absorb might not also emit, but…I have to say that I still don’t have a very clear picture of how gases emit and absorb heat. I always pictured the gas molecules as smashing around more quickly, in terms of linear motion. But clearly that’s wrong.
Commie:
Thanks for clarification.
I also meant to add that Ar is by itself & forms no bond, which is why noble gases are inert.
Perhaps I missed something here, but how is a measured quantity “not realistic”? Please tell me you did not actually mean to say this.
Anthony Watts,
I have been told that anyone can now post comments at the PSI blog since it has been opened up as I suggested.
I am the Moderator for that section but not a member of the PSI group.
Cheers.
[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]
It’s because of the windmill.
[Dupe entry? Mod]
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Sorry, the first one did not appear, so knowing that certain names trigger a delay I made some changes to provide a real time conversation.
Maybe you could improve your filter settings.
Crispin in Waterloo but really in Ulaanbaatar says:
May 29, 2013 at 11:18 am
@Michael Moon
“The Temperature of the Filament is the only temperature that matters here. Did the Filament warm from back-radiation? Did heat actually “flow uphill?””
Michael you are confusing heat conduction (which does not flow from colder to hotter objects) with electromagnetic radiation (IR) just as Postma has done. Radiation does not ‘flow’ in any particular direction based on the temperature somewhere else, only based on the temperature of the emitting object and its emissivity.
Crispin, heat transfer by radiation is no different from heat transfer by conduction – it always (that is, sponstaneously) flows from hotter to colder. The Sun’s thermal energy, its heat, is from a brilliant hot star millions of degrees centigrade which is constantly flowing out into the coldness of space. It flows in all directions, but, it is flowing in straight lines, and, it is travelling at the speed of light, so, the Sun’s millions of degrees heat is being transferred as longwave infrared radiation to us 93 million miles away in around 8 minutes. It is powerful, directed heat, energy, also known as radiant heat in traditional physics.
This is what we physically feel as heat from the Sun, we cannot feel shortwaves.
Understanding the difference between heat and light, (Heat and Light, and, Reflective and Thermal, are category differences of electromagnetic radiation in traditional physics), has enabled our scientists to design and build not only windows/film for windows which maximise entry to visible light while minimising entry to the direct heat waves from the Sun, thermal infrared, to save on air conditioning costs, but also to design and build thermal infrared heating for home and industry.
For example:
http://www.sunnyheat.co.uk/
“SUNNYHEAT infrared heating panels bring the warmth of the sun and low-cost heating into your home. It is the world’s first wirelessly controlled, ecologically-friendly long-wave infrared heating system. SUNNYHEAT infrared panels create biogenetic, invisible infrared waves; just as the sun has done for millions of years. SUNNYHEAT combines the power of the sun with high-tech development into a state to the art, energy-saving system designed to provide comforting warmth to the entire living or working space.”
http://www.sunnyheat.co.uk/infrared-heating.htm
“Infrared waves are part of the natural light spectrum from the sun, without skin-damaging ultraviolet radiation. NASA and other space agencies have utilized infrared heating technology and it has revolutionized health and beauty products all over the world.
“Infrared long waves are a form of light energy from the sun, but due to the longer wavelengths the human eye cannot see them. SUNNYHEAT panels emit infrared waves of 10.000 nanometers, which is within the “biogenetic” range. Biogenetic infrared energy is essential and beneficial for all living things.
Infrared long waves have the properties to penetrate, refract, radiate and reflect. This is the difference between infrared heating and the common convection heating methods.”
See the illustrations for the difference between convection and thermal, longwave, infrared.
http://physics.tutorvista.com/waves/infrared-waves.html
“The Infrared Waves Frequency range lies in between 300 GHz – 405 THz and hence the Infrared Wavelength is in between 750 nm – 1 mm. The 0.75-1.4 µm wavelength range of infrared region lies in near infrared region while the 15 – 1000 µm wavelength range lies in far infrared region.
“The infrared spectrum is further sub divided into five categories:
1.Near Infrared: The infrared region of the EM spectrum nearer to the visible region of the EM spectrum is known as near infrared region. The near infrared is not at all experienced by us since it is close to the visible spectrum and hence doesn’t have thermal characteristics; hence these waves are used in our electronic equipments like remote control, mobile phones as infrared ports.
2.Short wavelength Infrared: This region in infrared band is used predominantly for long distance telecommunication.
3.Mid wavelength Infrared: This band is used in guided missile technology. The head of the homing missile are designed to work under this region.
4.Long wavelength Infrared: This region is used for thermal imaging. The infrared sensors can obtained a full passive picture of anything in this range of infrared region.
5.Far Infrared: The region of infrared far from the visible region and nearer to the microwave region is known as far infrared region. The far infrared is being experienced by us in the form of thermal energy. Generally this region of infrared band is used in astronomy to detect the far flung galaxies and star which are very cold and cannot be seen in the above regions of the Infrared band.”
My italics. AGW has replaced the the direct heat from the Sun with shortwaves, mainly visible, and 1% of the total near infrared, (which is classed in with Light and not Heat, with Reflective and not Thermal in traditional physics). You do not have any direct heat from the Sun.
Visible light is not thermal, it is a much smaller wavelength than thermal and cannot do what the longwave infrared does. Visible light cannot move whole molecules of matter into vibration, which is what it takes to heat something up, this is a property of longwave infrared. Visible light does not convert to heat, but to chemical energy in the creation of sugars in photosynthesis, and from chemical into electrical impulses in sight – we have 137 million receptor cells per square inch in the retina:
“Visible light represents the only portion of the entire EMS which we can perceive with our eyes. These waves are just the right length to stimulate special cells in the retina (cones and rods) of our eyes which cause neural impulses to be sent to the brain.”
http://www.esrl.noaa.gov/gmd/outreach/lesson_plans/The%20Electormagnetic%20Spectrum-%20Visible%20and%20Invisible%20Light.pdf
“Perceiving Light
When light enters the eye, it first passes through the cornea, then the aqueous humor, lens and vitreous humor. Ultimately it reaches the retina, which is the light-sensing structure of the eye. The retina contains two types of cells, called rods and cones. Rods handle vision in low light, and cones handle color vision and detail. When light contacts these two types of cells, a series of complex chemical reactions occurs. The chemical that is formed (activated rhodopsin) creates electrical impulses in the optic nerve.”
http://science.howstuffworks.com/life/human-biology/eye2.htm
Visible light is simply not physically capable of heating land and water, it has other uses for life, and, as we get our great winds and weather systems from the intense heating of these by the Sun at the equator as heat flows to the cold poles, you not only do not have any direct heat from the Sun, you do not have any climate.
So what are you arguing about?
CommieBob:
On study, I see that “clarification” is too lame. Correction is better & significant difference best.
A seeming fine point that actually has important physical consequences when trying to gag down CAGW.
Thanks again.
Ok, I’m going to ask the dumb questions. These are aimed at refining the experiments and the arguments. To just to tip my hand, I think Watts et al are essentially correct and that Postma et al are operating on a misunderstanding.
First dumb question: Am I understanding correctly that we are modeling reflection of photons as if it were classical (Stef-Bolz) absorption and re-emission?
I seem to see that assumption in several places on both sides. On Postma’s side, he argues that radiation cannot reflect from a colder surface to a warmer on the grounds that Q = e(T_1^4 – T_2^4). Heat must flow from warmer to colder.
But this would appear to assume that reflection is nothing more than classical absorption and re-emission: energy is absorbed thermally, then radiated thermally, and the whole process is reflection.
IF the reflection process were absorption and re-emission, then Postma would be correct. But it is not. In fact, the classical theory cannot account for reflection. Reflection is a quantum phenonenon that is statistically controlled by the relative indices of refraction at the interface – temperature has nothing to do with it. The obvious experimental proof is to hold a mirror at a right angle to sunlight. The radiation from the sun is reflected directly back to the sun from the obviously colder mirror.
So Postma’s argument is based on a misunderstanding. It does not show that “greenhouse effect is impossible.” It only shows that reflection is not controlled by Srefan-Bolzmann.
Likewise, I seem to see that assumption in play in a couple of the experiments mentioned here at WUWT. Watt’s experiment places a mirror in front of a light bulb. The resulting reflected radiation causes a slight increase in the equilibrium temperature of the bulb. That’s fine, but it doesn’t test whether there can be a net heat flow (S-B) from a cold to a warm object. It *does* show that radiation can be reflected from a surface colder than the emitter, which in turn shows that reflection IS NOT classical absorption-reemission.
Likewise, the experiments described above in the article are not all testing the same phenomenon. The ones with the foil are demonstrating reflection. The ones with glass and black Al are demonstrating something closer to the greenhouse effect. (That these are different is immediately obvious from the difference in temperature results).
I had more dumb questions, but the wife is home, and she takes priority.
The bottom line is, if we are assuming that reflection is the same as classical absorption and reemission, it’s not. Stefan-Bolzmann is not relevant to the question of reflection.
I apologize in advance if I’ve misunderstood or misrepresented arguments on either side.
Gary Hladik says:
May 29, 2013 at 4:39 pm
Myrrh says (May 29, 2013 at 2:46 pm ): “Sadly, real world examples are blocked out of mind.”
It’s too bad that Myrrh can’t appreciate the delicious irony of that statement, having blocked the Herschel experiment out of his own mind. Here’s the backyard version (again), disproving his claim that visible light can’t heat matter:
http://www.ipac.caltech.edu/outreach/Edu/Herschel/backyard.html
It’s too bad that you’ve blocked out my explanation that size matters…,
that we’ve moved on a long way from the beginning of the discovery of invisible radiated heat from the Sun by Herschel’s first tentative measurements, to the fine tuning we have now, which knows empirically that even shortwave infrared is not thermal.
That’s why thermal infrared is called thermal, meaning “of heat” from the Greek, because it is the electromagnetic wavelengths of heat, not light. Near infrared is classed in with Light, not Heat and with Reflective, not Thermal.
That’s how near infrared cameras work – as visible light (Reflective, not Thermal), cameras work, by capturing the near infrared being reflected off the subject.
The AGWScienceFiction meme producing department keeps plugging Herschel, to stop you thinking.
Visible light is much tinier than radiant heat, than longwave infrared, Herschel was measuring longwave infrared overlapping the visible range, because his meaurements were still crude, were inexact.
Do you really want to be stuck in that time warp?
Why are windows and film for windows made which maximise entry of visible light and minimise longwave infrared? In the real world it is too keep the room cool. In your AGW fantasy world it is to heat the room.
This is supposed to be a science discussion, did you even bother to read what is being said here?:
usurbrain says:
May 28, 2013 at 3:51 pm
to: Curt says: May 28, 2013 at 3:05 pm
Then I wasted all the money I spent on that high dollar 3M Sun Control Film that only blocks 15% of the visible light and 97% of the IR? (ratings from 3M) The Sample they gave me seems near invisible. If So, why is my “sun” room (windows on 3 sides) 20-30 degrees cooler in the summer? Also wouldn’t this make all Solar Film a scam?
Should he sue the company?
[snip – name calling -over the top – Anthony]
[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]