Are high efficiency incandescent lights possible?

The advantage of incandescent light is that it puts out a pleasing continuous full spectrum, which so far have been very difficult for LEDs to match. But so far incandescent lighting has been less efficient at converting electricity into light than other types of lighting. Is it possible to increase the efficiency of incandescent technology? Incandescent technology has changed little over the last 100 years. If there were any simple way to improve the efficiency, it would have already been done.


Infrared Reflective Coatings

Halogen IR (or halogen infrared) bulbs increase efficiency by using a coating applied to the inside of the halogen capsule. This coating is designed to redirect some of the infrared energy back to the filament, which results in less additional energy being required to keep the filament hot and producing visible light



click link for diagram of how it works:
http://www.bulbs.com...n-IR-Bulbs.aspx

This commercially available IR halogen capsule, while currently more expensive, achieves an efficiency of 26 lumens per Watt.

Duro-Test was the first company to offer IR bulbs,
http://www.lamptech.co.uk/Spec Sheets/IN WC DuroTest 120-65G30IRC-E26.htm
http://news.google.com/newspapers?n...8MPAAAAIBAJ&sjid=3IwDAAAAIBAJ&pg=2698,1432584

One of the disadvantages though is that these infrared reflective coatings are usually ultrathin coatings of gold or silver.


Photonic Crystals

Photonic crystals do not obey the Planck Black body curve:
http://www.sciencene.../id/4290/title/

Guo Chunlei, associate professor of optics at the University of Rochester and his assistant, Anatoliy Vorobyev, used high powered lasers to create nano- and micro-scale structures on the surface of a regular tungsten filament. The tungsten filament is the small thin wire inside the light bulb. In doing this scientists can make the incandescent radiator 40 percent more efficient. The laser can also be used to make the light bulbs brighter and possibly even change their colors.
http://www.rochester...how.php?id=3385

My understanding of those photonic crystals is that, because of the spacing of the gaps in the lattice, only light that has a shorter wavelength than the gap length can escape. Most of the energy will be radiated from within as light before it has a chance to migrate to the surface and radiate as longer wavelength infrared. The problem, of course, is actually constructing these photonic crystals, since the spacing must be at such a small scale.


Candoluminsecence

What about candoluminescence? Like the thorium mantle used in camping laterns?

Candoluminescence is the light given off by certain materials that, when heated to incandescence, emit a larger proportion of their radiation in the shorter-wavelength visible spectrum rather than infrared, compared to a blackbody at the same temperature. Before electric lighting, "limelight" stage lighting was quite common. It used an oxygen-hydrogen flame to heat calcium oxide to give off a glowing white light. Could tungsten filaments coated with a thorium and cerium oxide coating to increase their efficiency?
Could coating the tungsten filament with a thorium dioxide coating prevent evaportation of the tungsten? Since thorium dioxide is a ceramic, it is not vulnerable to evaporation at high temperatures close to its melting point.

With the photonic crystal filaments, would it not be impossible to somehow fill the tungsten lattice structure with translucent thorium dioxide ceramic to prevent evaporation and degredation of the vulnerable fine structure?


Other Materials and Increasing the Temperature of the Filament

I was thinking about the idea of using molten tungsten as the incandescent source, contained within some translucent ceramic.
Thorium dioxide is a translucent white ceramic with a melting point of 3390 C (3663 K).
Tantalum nitride is a dark brown colored ceramic with which melts at approximately 3360 C. It is insoluble in water.
Unfortunately nothing seems to quite match tungsten's 3422 C melting point.
or perhaps someting like the Nernst lamp.

If the filament was immersed in a molten ceramic, it would probably prevent evaporation of the filament so that it could me operated much closer to its melting point.

Who said the incandescent conductor has to be a solid ? Of course, this would create technical challenges. Magnetic confinement might not be out of the question, since Lorentz forces induced by a strong current could keep the molten metal in the shape of a narrow filament. Or magnetic induction could be used to both simultaneously heat the molten metal to incandescence and to levitate it. Such a design would not be too complicated. Here is video of a homemade induction coil levitating a piece of aluminum until it becomes molten: http://www.youtube.c...h?v=Q6Zrnv4OtbU


Tunable Amplification

I had another idea. What about using a transparent conductor (such as indium tin oxide) and heat it to indandescence. It could then act as a sort of laser. By putting semi-reflective coatings on both ends to reflect back the vissible light, rather than the infrared, it would act as an amplifier, increasing the gain in the vissible light radiation, and shifting the Planck black body curve. The transparent conductor would still have to be very hot, but it might not have to be as hot as a tungsten filament because of this shift. The concept would be similar to a tunable laser. By putting reflective coatings on just two sides of the transparent conductor, the light source could even be made directional like LEDs.

I am fairly sure population inversion would not be an issue here. Have you never seen the picture of a heat-insulating ceramic material that has been heated to white hot in a furnace, then allowed to cool. A researcher is holding the cube of this material by two corners with his unprotected fingers, while light is coming out of the sides of the cube. The inside of the ceramic cube is still glowing hot, and the light is making its way out the sides. http://www.youtube.c...feature=related
If the conductor is transparent, and the light generated from incandescence, then the conductor will not absorb at any particular frequency. Also, not all types of lasers need to achieve population inversion. In some cases, the absorbing atom immediately decays to a lower excited state, and it is this lower excited state that undergoes the stimulated emission. An example of such a laser is the Nd:YAG that is used in common green laser pointers to create an infrared beam before it is frequency doubled to green.

No. See insta-flash.
Incan have a continuous, but incomplete and unbalanced spectrum. That was covered in the other thread.

This is like looking for the world's best carburetor... let it go man.

The maximum possible efficiency for any type of incandescent is 95 lumens per watt. This is at a filament temperature of 6600K. No known material can withstand this temperature for even for a fraction of a second. Even if we had such a material, most people would find 6600K unacceptable for general lighting. That would imply lower filament temperature/reduced efficiency. LEDs have already exceeded 250 lm/W in the lab. They just reached 200 lm/W in production. You can get excellent color rendering with LEDs at any desired CCT, albeit at reduced efficiency, by carefully choosing phosphors. There are commercially available LEDs with CRI > 90 and efficiencies approaching 100 lm/W (or even exceeding 100 lm/W at lower drive currents). This is better than is possible with incandescent technology, even assuming you had filament material which could withstand 6600K. Moreover, the lifetime of LEDs is tens of thousands of hours. In short, there is absolutely no point trying to design a more efficient incandescent lamp now. At best it will be lower efficiency and shorter lifetime than LED. Also, given the need for exotic materials or processes, such a lamp would most likely cost more than LED. Like CRTs, steam locomotives, internal combustion engines, etc. , incandescent lighting is a dead/dying technology.

No.

I see 30 lm/watt and "40% more" (45 lm/w) cited. The others seem to be estimates, unless they have disjointed spectal power distribution. So: you can make it a bit more efficient, but far below the least efficient production LED or fluorescent unit.

Did you quote any sources showing how to reach a comparable efficiency to last-gen LED with a producible process? Nope. Good luck.

jtr1962 said:

... Like CRTs, steam locomotives, internal combustion engines, etc. , incandescent lighting is a dead/dying technology.

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but steam locomotives are pretty cool and impressive!! Will we ever look back on incandescent bulbs with the same romanticism? Well, I guess we already consider candles to be classically romantic, so I withold judgement on incandescents. Better keep a few small ones around for the kids' birthday cake.

jhellwig said:

No.

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ditto. nope.

bulbs with filaments....they work, and are simple, cheap, and non toxic, but to get any real 'efficient' light
out of a bulb you need to go with a gas discharge lamp...and these are still a bit wasteful compared to LED.

Steve K said:

but steam locomotives are pretty cool and impressive!!

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As a railfan I agree wholeheartedly! A steam locomotive is a living beast, while a diesel or electric locomotive is merely a transportation appliance (albeit one which still has some personality). Steam locomotives are certainly worth preserving for the occasional railfan trip even if they'll never again be practical for day-to-day use.

Will we ever look back on incandescent bulbs with the same romanticism? Well, I guess we already consider candles to be classically romantic, so I withold judgement on incandescents. Better keep a few small ones around for the kids' birthday cake.

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I somehow doubt incandescents will ever be looked back upon with the same rose-colored glasses we might see steam locomotives with. Steam locomotives still fascinate everyone, even those born long after they disappeared from the rails. Incandescents might evoke youthful memories of some people who may have grown up with them, but then again they're just not in the same league as a steam locomotive. Candles are sometimes considered romantic because in a way they have a bit of personality. The flame flickers randomly, no two candles are exactly alike. Incandescent lamps are all more or less just glowing mass-produced pieces of wire. On the most common frosted ones you can't even see the filament, just a glowing globe which can just as easily be fluorescent or LED.

jtr1962 said:

I somehow doubt incandescents will ever be looked back upon with the same rose-colored glasses we might see steam locomotives with

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I don't know, steampunk is pretty popular with many geeks at the moment, and there are already "nostalgia" incans available at Lowes, the ones with long, multi-looped filaments. If LED's are able to mimic the output spectra of incans, including the color shift as they are dimmed, then there is only the "look" of the filaments and glass of the bulbs themselves to recommend them.

But I would not be surprised to see the market for these old, shall we say "analog" lights persist well past the final practical demise of the technology in the face of the ubiquitous "digital" LED lights. There will always be "luminafiles" who swear that they can see the "digital roughness", the little peaks and valleys of LED lights, or who swear that the tiny contribution made by >780nm deep red light makes all the difference in the world, who will insist that their analog turntables be lit in the warm yellow glow of incandescent lights.

Canuke said:

But I would not be surprised to see the market for these old, shall we say "analog" lights persist well past the final practical demise of the technology in the face of the ubiquitous "digital" LED lights. There will always be "luminafiles" who swear that they can see the "digital roughness", the little peaks and valleys of LED lights, or who swear that the tiny contribution made by >780nm deep red light makes all the difference in the world, who will insist that their analog turntables be lit in the warm yellow glow of incandescent lights.

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I'm sure that will happen in much the same way you still have tube amplifiers being made in small quantities these days to market as niche, expensive products to people who insist they're better. I'd be very surprised however to see any incandescents being sold in mainstream stores by the end of the decade, if not sooner.

All that said, I personally think the recent fascination with all things retro is just another passing fad. If I had to give a reason for it, I might say that it's because right now nations are just not involved in large-scale forward-looking endeavors which keep people interested in new technology. For example, back in the 1960s when the space race was on, it seemed like society couldn't get rid of anything related to old technology fast enough. Of course, that led to some questionable decisions like the demolition of Penn Station. Granted, newer isn't always better, but neither is older. Nothing wrong with keeping bits and pieces of old tech around for the sake of history. I just can't see continuing to use it regularly if the newer alternatives are better in many or all respects.

The only problem with the relentless pace of advancement these days is items usually become functionally obsolete long before they wear out.

Well just because it is appropriate, I have to write one of my favorite sayings:

"The definition of insanity is to keep doing the same thing over and over again and expecting different results ....."

Anders Hoveland said:

The advantage of incandescent light is that it puts out a pleasing continuous full spectrum

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- We can debate pleasing to the cows come home, but let's just stick with this statement "pleasing continuous spectrum"

Anders Hoveland said:

which so far have been very difficult for LEDs to match

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- Not really true. Xicato Artist series, Bridgelux 97 CRI series -- all very very INCAN like. Problem is, most of the market wants lots of lumens with good quality light, not less lumens with great quality light. Will that change? ... Yes when LEDs get a bit more efficient.

Anders Hoveland said:

Photonic crystals do not obey the Planck Black body curve:

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- Violates your first point of continuous "pleasant" spectrum

Anders Hoveland said:

Candoluminescence is the light given off by certain materials that, when heated to incandescence, emit a larger proportion of their radiation in the shorter-wavelength visible spectrum rather than infrared, compared to a blackbody at the same temperature.

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- Violates your first point of continuous "pleasant" spectrum

Anders Hoveland said:

Magnetic confinement might not be out of the question, since Lorentz forces induced by a strong current could keep the molten metal in the shape of a narrow filament.

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- Correct me if I am wrong, but you are no longer talking about "Incandescence" so much here as a plasma ... of which there are better ways to implement this

Anders Hoveland said:

What about using a transparent conductor (such as indium tin oxide) and heat it to indandescence. It could then act as a sort of laser. By putting semi-reflective coatings on both ends to reflect back the vissible light, rather than the infrared, it would act as an amplifier, increasing the gain in the vissible light radiation, and shifting the Planck black body curve.

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- I don't think you thought this one through. Lasing and incandescence act much different and lasers don't amplify even though it is in their name. It was a misnomer from trying to relate it to a maser. If you reflect back the visible light ... then it is not letting light out ... and if you are letter infrared out ... (and other wavelengths), then there is nothing make it hotter ..... which is needed to have visible light. There would be no gain, there would only be losses.

- Let me put it another way ..... it's like thinking that a 100 watt bulb in a room of mirrors (partially coated or not) would somehow put out more lumens



Virtually every one of these "ideas" would change the spectrum such that it no longer looks like a blackbody curve and while doing it only achieve so-so efficiency. Not sure why you would want to do that when we can already achieve either very high efficiency with tolerable quality, or good efficiency with excellent replication of the blackbody curve.

It like coming up with an amazing new way of making solar cells ... that are 3% area efficient and will never get much better. Not much point.

Semiman

Those halogen IR lamps actually have a CRI more like 97 rather than 100. Also these IR lamps are incredibly fragile due to the suspectibility of hot shock, since the filament coils have to be very closely spaced in order to be compact enough in order to be correctly spaced to get the IR onto the filament, it is lost if the filament was out of place even by a few degrees. Hot shock means the filament shorting out when subject to vibration. Even the standard incandescent bulbs are much more fragile than the original carbon filament lamps. The old carbon filament lamps were so durable than even shorting out the filament will leave it intact, but then they are terribly inefficient at only 4 lumens per watt max and a very orange yellowish light at around 2000K. Even 100 years ago there were engineers who knew the carbon filament lamp was too yellow. Check out this interesting link:

http://query.nytimes.com/mem/archive-free/pdf?res=F00D11F63E5A15738DDDAA0894DA405B878CF1D3

The Helion lamp was by the way a carbon-silicon filament lamp but it was never sold. I think it was actually a little more efficient than today's tungsten lamps but still not quite as high as LED.

jtr1962 said:

... LEDs have already exceeded 250 lm/W in the lab. They just reached 200 lm/W in production...

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Drifting the thread slightly, what is considered the theoretical max for LED? A while back, wikipedia said it was 250-300 lumens/watt. But that statement disappeared last time I checked.

... Like CRTs, steam locomotives, internal combustion engines, etc. , incandescent lighting is a dead/dying technology.

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Steam train buff here too.

If LED hadn't come along, I too would be stockpiling incandescent bulbs. (Well, halogen versions at least.) Fortunately there are some amazing LED products available now. Costs continue to drop. I've even started replacing some of my fluorescents with LED.

You asked about the theoretical max for LEDs. If Holonyak is correct about LEDs having a 100% quantum efficiency, then the limit would be anywhere from 242.5 LPW (for a CRI of 100 at 3600K) to 683 LPW for the monochromatic 555nm spectral line, the yellow-green color that the human eye is the most senstive to. The limit will depend on the type of spectrum and the CRI. However, 100% quantum efficiency can't be achieved with phosphor based white LEDs due to the stokes effect in the conversion process from UV and/or blue to white light. They will still far surpass the efficiencies of traditional fluorescent and HID light sources, however.

By the way, 100w-equivalent 50w halogen IR lamps in an A-19 shape that emit 1650 lumens (that is 33 lumens per watt, impressive by incandescent standards, only the 3-4 hour life 3400K photofloods rival that efficiency) and rated at 1500 hours, twice the life of 100w bulbs, are just starting to be available for $3.50 apiece. They probably won't compete with LEDs eventually but I will buy a few for my collection. Maybe they will look better in fixtures meant for clear lamps than LEDs however.

oldwesty4ever said:

You asked about the theoretical max for LEDs. If Holonyak is correct about LEDs having a 100% quantum efficiency, then the limit would be anywhere from 242.5 LPW (for a CRI of 100 at 3600K) to 683 LPW for the monochromatic 555nm spectral line, the yellow-green color that the human eye is the most senstive to. The limit will depend on the type of spectrum and the CRI. However, 100% quantum efficiency can't be achieved with phosphor based white LEDs due to the stokes effect in the conversion process from UV and/or blue to white light. They will still far surpass the efficiencies of traditional fluorescent and HID light sources, however.

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Thanks! What about the blue LEDs used to generate white light?

I saw this article the other day about tripling the efficiency of Tungsten filaments.

Photonic Crystals Reinvent Tungsten Light Bulbs:
http://www.technologyreview.com/view/509021/photonic-crystals-reinvent-tungsten-light-bulbs/

The filament used in the Nernst lamp was a zirconia ceramic (also containing some yttrium oxide) which becomes electrically conductive after being heated. As the filament was a ceramic, it could operate in air. Zirconia melts a 2715 °C.
http://www.youtube.com/watch?v=uGxSwumcFtU

I do not know if tunable gain, using reflective coatings, would be possible with a nernst filament. At these higher conductive temperatures, the ceramic might not be transparent anymore. I do not know if it is possible to make the yttrium-stabilized zirconia translucent, or if some sort of incandescent laser is possible. Trying to combine IR coatings with tunable coatings, both for higher efficiency, might make things complicated, since it would be undesirable for the infrared to be amplified, and this would defeat the whole purpose of the tunable coating. A laser design would make this easier, since we could reflect and amplify the desired vissible frequencies in one direction, and then put an infrared-stopping coating on the ceramic rod so that the infrared heat being reflected out in other directions could be returned back as heat, but not as infrared frequencies that could cause amplification.

AnAppleSnail said:

So: you can make it a bit more efficient, but far below the least efficient production LED or fluorescent unit.

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Multiple strategies could be combined together. Even if each one only adds 20-50% efficiency, combined they have may have a compounding multiplying effect.

This halogen is 24 lumens per watt, with a lifetime of 2000 hours, I am sure that could be much higher if the lifetime was reduced and an IR coating was added.
http://www.lamptech.co.uk/Spec Sheets/TH DJ Q1000T38C-230 Philips.htm
Plus, I doubt that bulb even has xenon in it, further increase in efficiency if the lifetime is held constant.

AnAppleSnail said:

So: you can make it a bit more efficient, but far below the least efficient production LED or fluorescent unit.

Did you quote any sources showing how to reach a comparable efficiency to last-gen LED with a producible process? Nope. Good luck.

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Yes, if you just want efficiency, it is easier to go with LED. But to make an LED lamp that matches the spectrum of incandescent light is a little more complicated. The question is whether such an LED lamp would be simpler and less expensive than the theoretical high efficiency incandescent lamps being discussed here. This may have been what General Electric thought, when they decided to scrap their HEI research to concentrate on LED.

Incandescence is as related to lasers as paper airplanes are related to bison. And I'm not sure that I want any LED lights that match the light output of hot metal. Putting reflectors on a filament will either contain light or have little effect. Transparent ceramics are usually 95% transmissive or lower when new.

Suppose you want to make a sandwich 200% tastier. Research shows that adding jelly makes it 30% better, pickles 50% better, jalapenos 40%, extra strong swiss 30%, Mustard 30%, bacon 20%, honey glaze 30%, and bean sprouts with mayo 30%. Will doing all at once be amazing? No. additive percent strategies usually compete with each other. Hedging your bets in performant materials almost always decreases their ability. A filament covered in an effective reflector to trap heat is expensive (and not a laser!). A filament with nano structures is touchy to make. The non-incandescence ones lack your arbitrary criterion for being serious light sources.

If you like boiling metal's glow, great! But it's not yet been cost effective to do this weird science routine on it. As a compromise, so far these advances can only take away the filament bulb's main selling point: very low up front cost.

We can probably make an incandescent right now which gets >60 lm/W. How? Use IRC for starters. Second, run the filament at close to maximum temperature, say around 3400K. The problem is such a lamp will be costly and only have a lifetime of a few hours. It would be a major commercial failure. In fact, any efforts to increase the efficiency of incandescents negate their only real advantage over other lighting technologies-very low cost.