Return of incandescent light bulbs, more efficient than LEDs

Discussion in 'General Science & Technology' started by Plazma Inferno!, May 27, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

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    Ever since the EU restricted sales of traditional incandescent light bulbs, homeowners have complained about the shortcomings of their energy-efficient replacements.
    The clinical white beam of LEDs and frustrating time-delay of ‘green’ lighting has left many hankering after the instant, bright warm glow of traditional filament bulbs.
    But now scientists in the US believe they have come up with a solution which could see a reprieve for incandescent bulbs.
    Researchers at MIT have shown that by surrounding the filament with a special crystal structure in the glass they can bounce back the energy which is usually lost in heat, while still allowing the light through.
    They refer to the technique as ‘recycling light’ because the energy which would usually escape into the air is redirected back to the filament where it can create new light.

    http://www.telegraph.co.uk/science/...nt-light-bulbs-as-mit-makes-them-more-effici/
     
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  3. billvon Valued Senior Member

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    Hmm. LED's are available in any color you like (including warm white) and turn on instantly.
    "Return of incandescent light bulbs, more efficient than LEDs."
    Hmm. You'd have to improve incandescent light by over a factor of 10 to make them competitive with LED's. I don't see that happening with nothing more than reflectors.
    Well, no. Light bulbs are blackbody radiators (as is the Sun) but sunlight would result in that "clinical white" light referenced above. They also do not share the same spectrums, since they are different temperatures, and the filtering that goes on in our atmosphere changes the spectrum dramatically anyway.
     
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  5. Q-reeus Banned Valued Senior Member

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    Photonic crystal (PC) is the common 'game-changer ingredient' mentioned in another current thread:
    http://www.sciforums.com/threads/doubling-the-amount-of-energy-generated-by-solar-cells.156499/
    However, unlike that case where the dictates of a straight power balance makes the base notion absurd, here it can be made to work. A relatively large sheath of PC surrounding a relatively concentrated source ~ 3000K Planck spectrum radiator allows reflective recycling that will dramatically bump up spectral efficiency over that of raw radiator.
    Problem is the prototype shown in article seems to use sandwiching PC layers in intimate contact with tungsten film radiator. In that case, 'recycling' just doesn't make any sense. So just how it pans out in practice will be interesting. And yes as per #2, the true standard for natural lighting is ~ 5800K sunlight, and ~ 3000K tungsten is strongly biased to the red end of spectrum. Which may be a good thing to absolutely minimize any UV damage to eyesight, but does not provide a natural rendition of colours.
     
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  7. Q-reeus Banned Valued Senior Member

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    Going to the Nature Nanotechnology article: http://www.nature.com/nnano/journal/v11/n4/full/nnano.2015.309.html
    it becomes evident basically the same team is involved in both the incandescent and PV projects cited last post. Hmmm.... So I magnified up and screen captured the 2 pics available in review. Seems they really expect to achieve high efficiency by just a simple sandwich arrangement. At first that seemed hopeless, but on a closer think it amounts to reducing drastically the input power required to maintain a given film emitter temperature. With escaped radiation in the correct visible spectrum, there really can be a significant gain in efficiency. Expense seems a bigger issue as to get near hoped 40% efficiency, several hundred layers of multi-index film are required. Can't see that ever being cheap.
    I also note they are not really using photonic crystals - just multi-layer films, which however can certainly be highly effective as frequency filters.
     
    Last edited: May 28, 2016
  8. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Are you saying they will attempt the decades old approach of getting an emitter with better spectral match to the PV band gap, as I described here? http://www.sciforums.com/threads/do...generated-by-solar-cells.156499/#post-3382988

    However, instead of heating the hot emitter with sunlight, they will use electric power.

    Yes multi-layer dielectric films* can be transparent only for the wave lengths that match the silicon PV's band gap, and the other wave lengths are mainly reflected, but not back to a small point-like hot source only, unless the multi-layer film is concave, not plane. That would greatly increase the cost of the multi-layer film, if it is even possible to make them with the individual layers of constant and precise thickness.

    To avoid that, it sounds like they plan a small 2D, electrically heated, hot emitter, with multi-layer films on both sides, in very close proximity, but not actual contact, with the hot 2D emitter. That would make most of the useless (for PV cell) thermal radiation be reflected back onto the hot emitter and reduce the needed electric power to keep it hot; However, multi-layer films are not perfect. In addition to transmitting the desired wave length and reflecting the "useless for PV cell" wave length, they have some absorption and will be come as hot as the emitter when thermal equilibrium is reached and when that hot, they will also be emitters of basically black body radiation.

    They could just use one multi-layer film on one side of the 2D emitter, and a metalic reflector on the other side. That would make it easier for all to understand that the close metalic reflector, would get very hot (just like their dielectric film does) and also radiate a spectrum.

    I. e. the radiation emerging towards the PV cells will be a spectrum, not just the wave lengths matched to the band gap.

    Also not mentioned and adding to the cost, is fact this all this must be in vacuum, to avoid internal convection of the thermal energy to the walls of the "light bulb." Just like an ordinary incandescent light bulb, even in vacuum, the glass envelope will get quite hot and make convection currents in the air.

    It is hard to tell exactly what they plan (perhaps on purpose?). But clever ideas that cost much more than the existing electric light sources have no commercial future.

    * Yes you are correct. The alternate layers must have different refractive indies, as different as feasible with carefully controlled thickness. Very expensive if speaking of dozens ot layers.
     
    Last edited: May 28, 2016
  9. Q-reeus Banned Valued Senior Member

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    That PV thread was invoked here just as a reminder the same basic team imo got it badly wrong there, so be somewhat skeptical here too. In hindsight, that just confused things, and my initial skepticism this case was unwarranted. I was thinking in terms of what happens if the input power is unchanged and 'photonic crystal' is then added. It would all go critical and vaporize or attempt to. Then it dawned the real approach was to reduce input power while retaining emitter temperature, which is sound.

    Regarding your 1st para in quoted post, I refer you to my following one #11, especially playing around with interactive app that gives a startling visual of just how poorly useful silicon PV wavelength band is utilized by passing through a filter from ~ 1000K thermal emitter. A small fraction of 1% of IR power which is a joke.
    However, rereading the OP article there, I realize now two different concepts were being presented as though the same - passing incident solar radiation first through standard silicon PV cell before waste heat then absorbed and re-radiated to a second cell - or absorbing all incident power and re-radiating to just one cell. I based my criticism on the latter idea. The former one seems to be what they actually used and would allow a quite modest overall gain if say a germanium PV cell was the second one receiving the re-radiated waste heat. But as you say tracking technology for one will make it not generally cost attractive.
    Sure. I was thinking along the lines you mention below, that at high energy densities the 'photonic crystal' would heat up and just blackbody radiate. Hence the need to dilute incident radiant power at the 'photonic crystal' i.e. multi-layer dielectric film. But not really needed as long as transparency is high enough.
    Yep, but note this is not here about PV application just incandescent lamp efficiency boosting.
    As mentioned earlier, that was (partly) my reasoning in suggesting relatively large surrounding reflecting surfaces - reduce incident power such that hot emission of film not an issue. But at ~ 3000K emitter temp, fraction passing through in correct band at ~ 5% is sufficiently high that weighted average reflector film absorption coefficient of less than say 0.02 over reflected IR band, is likely feasible and would not lead to runaway heating of film.
    Yes but tailoring can be made pretty good with enough computer optimized stack layers. The real issue imo is that at ~ 1000K, spectral fraction for PV use is just very poor (germanium) to extremely poor (silicon).
    Yep that's the ideal, although suppression of tungsten evaporation as in halogen lamps would likely still be used and would entail some mix of e.g. krypton/iodine to avoid the 'blackening'.
    Exactly.
     
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Not sure Q-reeus said that a receiving target can get hotter than the source heating it by radiation. Parts of text seem to imply that; but that is impossible.

    If it were possible you could get more useful energy than the Carnot limit by running the thermal engine from the hotter seondary than from the primary that was heating it.

    Q-reeus said: "The former one seems to be what they actually used and would allow a quite modest overall gain if say a germanium PV cell was the second one receiving the re-radiated waste heat."

    People, with plenty of money and limited collector surface, wanting more efficient conversion of sunlight, have made tamdom PV cells. Behind the first silicon one is a germanium one, which gets the unabsorbed sunlight with wave length too long to be useful to the silicon PV cell but is partially energetic enough to raise and electron up across the smaller germanium band gap. I don't think letting the photon energy that passes thru the first PV cell degrade into heat could be as efficient as using it as photons.
     
    Last edited: May 28, 2016
  11. Q-reeus Banned Valued Senior Member

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    Never said that and maybe you have confused what second line in #6 was saying - at constant input power, adding multi-layer reflection would cause a catastrophic rise in filament temperature.
    Actually, I theoretically proved back in mid 90's it's possible, via combining two quite old classical optics principles, to concentrate completely incoherent incident radiation - applying to a uniform temp environment. It was never pursued owing to the inherent low radiant energy densities at room temp where it might have otherwise found practical use. And if used to concentrate e.g. incident solar, regular optical methods via lenses or mirrors would always be more effective, cheaper and easier.
    [Chew over this: https://www.osapublishing.org/oe/abstract.cfm?uri=oe-18-16-16646&origin=search
    They don't outright claim 2nd Law violation - for some reason.]
    The MIT team claim their system boosts the overall gain compared to a regular tandem cell. At obviously greater cost and complexity.
     
    Last edited: May 29, 2016
  12. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Your link's creation of a black hole for sun light is no big deal. That is easy; but not the real problem.
    What I said was: It is impossible to heat a target with radiation from a source to higher temperature than that of the source.

    Certainly it is possible to absorb 100% of the light incident upon a target. In fact more than three decades ago I was issued US patent 4033118 (mass flow solar absorber) which does exactly that. It may be the world's most efficient solar thermal system. I think it is.

    Yes if you can completely absorb all the incident radiation, and it is highly concentrated sun light, you can produce very high temperatures, but never hotter than the source. What I think is clever about my inventions is that it can get very hot, limited by the soften temperature of quartz, yet loses very little of the absorbed energy by IR radiation.

    Most solar energy systems for producing power are trapped in a "catch 22" If very hot for good Carnot limited conversion efficiency, they are also strong radiators of IR. Prior to my invention there were several attempts to solve this "catch 22" problem, all using wave length selective filters. Filters that let the sun light pass thru, but reflected the IR trying to escape from the hot absorber. That works well if the filter is not in significantly concentrated sun light, but then the filter must be physically large, and that is an economic killer.

    Some tried to place a smaller, affordable filter in the highly concentrated sun light but as all filters have some absorption, the filter becomes very hot, and it re-radiates the IR. Worse in practical conditions, rain or even hail can fall from the over head sky while sun light is still entering the system. The thermal stress, with cold rain or ice falling on the very hot filter destroy that expensive filter. (Small pieces fall to the ground from its holding frame.)

    My invention has none of these problems. The wave length selective filter is just a long tube (Say length > 20 diameters) The entrance end part of the tube is glass (but in the very hot parts distant from the entrance, a quartz tube, with a smooth transition between as the “glass grades into quartz") with a reflective film on the outer surface. I. e the highly convergent sun light is focused on the open end of the tube but becomes divergent once inside the open end. Then at various locations deeper into the tube, the sun light passes thru the glass with little absorption and reflects on the outer surface film, back into the tube and later when still deeper into the tube, passes thru the glass wall twice again (reflected once on the other film) etc. many times. With each passage thur and back thru the wall there is a little heating of the wall but the absorption is spread over a huge area compared to the entrance hole.

    There is a concentric outer tube and the "working fluid" flows in the annulus space between these two tubes. From the solar entrance end towards the hotter more remote end, picking up thermal energy from the walls as it goes and becoming ever hotter.

    The IR, which is intense and filling the tube far from the entrance with black body radiation, can not "mirror" its way back out of the tube and escape as the walls are not transparent to the IR - The IR can't see thru the walls to reflect on the film covering the outside of the inner tube.

    I published two papers in Applied Optics giving the mathematical analysis of all this. One focused on how the sun light is reflected ever deeper into the tube (and the wall heating it makes as it goes down into the tube). The other on what happens to the IR trying to escape from the hot black body radiation filling the deep end. It of course, is mainly reabsorbed in the wall, and adds to the local wall heating.

    The only significant IR that can escape is that very narrow solid angle, a tiny fraction of the total of the black body radiation that happens to be headed directly towards the open end of the tube, where the concentrated sun light is entering.

    Thus I described an absorber which is a “black hole” for sun light and gets very hot, yet has very small fraction of the absorbed energy, lost by re-radiation of IR.

    The patent also tells how to chemically store the energy in the “working fluid.” Much better than thermal storage as passage of time does not “drain energy away.”
     
    Last edited: May 29, 2016
  13. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Here is most of the summary of theoretical paper at: https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-18-16-16646&id=204042
    Sited by Q-rees in his post 8:

    "In summary, we have developed a theoretical description of wave propagation in cylindrically-symmetric gradient-index systems, and applied this approach to light “trapping” in the recently proposed electromagnetic black hole concentrator and absorber.

    In particular we have demonstrated that an approximate lamellar black-hole with a relatively limited number of homogeneous layers, while giving the desired ray-optical performance, can provide absorption efficiencies comparable with those of ideal devices with smooth gradients in index. It is forecasted that the use of non-uniform layers could further improve the performance of the lamellar device with a given number of homogeneous layers."

    The part I made bold is very expensive, if it is even possible to achieve. They tacitly recognize this and suggest in second paragraph of the above summary that sets of concentric cylinders, each of different but uniform index of refraction, is an approximation to their theoretical ideal.

    I grant than essentially perpendicular light incident from the side of their cylinder can be trapped (except for the small fraction that reflects on the outer surface, typically about 4%). I. e. They have designed a "quasi black hole" that absorbs about 96% of the light incident up on it. No quite as good as the open end of a tube, which has no surface to reflect light away. I. e. not as good as the absorber I invented and patented, and described briefly in post 9, which is truely a 100% black hole.

    However, as I noted in post 9: (making a very black absorber) is not a significant problem. Even some “black paints” on a micro-rough surface can do as well as they do!.

    The true problem for ALL solar thermal systems is:

    How to get the absorber very hot for good Carnot conversion efficiency and yet not have a large fraction of the absorbed energy just re-radiated away as IR? What I called the "catch 22" of almost all solar thermal systems! Most re-radiate away more power as IR than they produce as electical energy!

    My invention solves that problem, not perfectly but nearly so, for any tube with length > 10 times the diameter of the sun light entrance hole.
     
    Last edited: May 29, 2016
  14. Q-reeus Banned Valued Senior Member

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    Billy T, or should I say William Powell, thanks for patent # - found it and a number of interesting ideas there. You have gotten the wrong drift re that cylindrical 'black hole'. Even perfect absorption is indeed not that much of a big deal. What is a big deal there is that the concept lends itself to the concentration of *isotropic, incoherent, random radiation of a uniform temp environment* - i.e. breaks the 2nd Law. Practicality is another matter. You will need to sit back and think about it some. Not the right thread to go into it any further though - this has gotten way off topic.
     
  15. Edont Knoff Registered Senior Member

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    That's good news. It wasn't meantioned in the original message, but LED and the luminescent tubes don't provide a continuous spectrum, but glowing filaments do. Even that I use a lot of LED lights to save energy, a continuous spectrum light of similar efficiency will be very welcome.
     
  16. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I agree we need to drop this diversion, but must note that the 2nd law would be broken only if their concentration scheme could produce a temperature higher than the source - they don't claim that and it can not.
     
    Last edited: May 31, 2016
  17. Q-reeus Banned Valued Senior Member

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    Your absolute faith in the 2nd Law is of course likely shared by those theorists. To me it's bleeding obvious a *virtually omni-directional concentrating lens speaks otherwise. In a way it's good no-one else here sees it like that. Faith.
    * [go from cylinder to concentric shells sphere, and one has a purely omnidirectional concentrator lens.]
     
    Last edited: May 31, 2016
  18. billvon Valued Senior Member

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    Keep in mind that that's the problem; that's why incandescent bulbs are so inefficient. That "continuous spectrum" contains a lot of non-visible light. Indeed, the proposals above cause the spectrum to become discontinuous, changing the shape of the spectrum curve.
     
  19. exchemist Valued Senior Member

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    That's true of course, when speaking of a source that emits due to black body radiation.

    But what strikes me about this is that if one has a source that emits, say monochromatic or narrow -band radiation by some process other than black-body emission, then that would not apply. For example, if one irradiates something in a microwave oven, the energy is initially absorbed at a narrow band of frequencies, but then redistributes itself by relaxation, until a Maxwell-Boltzmann energy distribution is reached. This will populate energy levels significantly above the original microwave transition excited by the radiation.

    So it seems to me perfectly possible for "recycled" IR radiation to accumulate to a point at which some repopulation of visible emission levels occurs. To put it another way, as soon as you introduce photonic crystals into the system, you don't have a black body any more.
     
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    What should be equally obvious to you is that as the absorber gets hotter, radiation can leave it by exactly the same paths that the radiation heating it used to enter. If it were to become as hot as the source, then the flux from it and the flux to it become equal and it gets no hotter.
     
    Last edited: May 31, 2016
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes. They can reduce the electrical power needed to keep the hot filament (or 2D radiator) radiating at a certain power level in the visiable, if some of the IR that tries to escape from it is reflected back and absorbed by it.

    My statement was about relationship between temperatures: That of a target being heated by a radiant source and that of the source, which need not be a black body radiation for my statement to be true.

    When the source is monochromatic, it becomes some what problematic to define its "temperature." Temperature is a concept defined only for equilibrium or at least “steady state” conditions. One way to define the temperature of a LASER beam is to let it pass thru a very small hole in the wall of an otherwise closed hollow box, made with highly conductive walls, like a copper box, WHICH IS PERFECTLY INSULATED. - Has no thermal loses thru the copper walls; only radiative losses out of the small hole.

    Eventually the radiation emerging from that hole will have the same power flux (in a black body distribution) as the LASER beam's flux entering the hole has. Then an equilibrium has been established and temperature of box and LASER are the same as there is no net heat transfer from one to the other. (That is what equal temperature of two objects in thermal contact, only with each other means by "equal temperatures.")

    What I have been stating as true, is that the box can not be hotter than the Laser beam. I. e. the energy the box radiates out of the hole can not be more than enters the hole.

    If you want to construct some other reasonable definition of the "temperature of a monochromatic source" feel free to do so, but what I stated will still hold true. If it did not, you would violate even the first law of thermodynamics (conservation of energy).
     
    Last edited: May 31, 2016
  22. exchemist Valued Senior Member

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    I think that's more or less the same point I was making. If you have a source that does not radiate according to the black body distribution curve then you have a source which is effectively not at thermal equilibrium, as far as its emitted radiation is concerned and thus for which temperature is undefined. That's what I believe we have in this case, due to the ability of photonic crystals to pass only certain bands of incident radiation.

    But I have trouble with your attempt to define a temperature for a laser beam. It seems to me that it does not have any defined temperature at all, because its emission reflects a population inversion, which is not a body at thermal equilibrium. I see what you are trying to do, but all you end up with is saying the "temperature" of the beam is the temperature to which it can raise this box of yours. This will be proportional to laser radiation flux, i.e. the size of the laser, and nothing to do with its temperature in any normal sense.

    Would you try to establish a "temperature" for the microwave emission from a cavity magnetron in the same way? What's the point?
     
    Last edited: May 31, 2016
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I think we fully agree. I said temperature only exists in thermal equilibrium. I suggested one way it could be defined for non-black body radiations as my statement that “target can not become hotter than the radiation source heating it,” needs some definition of the source temperature, when not a black body radiator.

    It is no problem that the size of a LASER will change the constructed value of the temperature assigned to it, because: There is no "temperature in any normal sense" - when speaking of the beam. If speaking of the source, then with inversion of the normal thermal populations, those level populations have a negative temperature. Few are happy with the concept of a negative temperature (and it too is a defined one). I find it useful as a measure of how great the population inversion is.
     

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