What Will The Future Bring?

[2xTrinity]

LED manufacturers need to take a little step back from the efficiency war and try to broaden the spectrum. Natural white needs some work in the LED domain.

The two aren't mutually exclusive -- improvements in efficiency, particularly in the blue dice, lead to efficiency improvements in ALL white LEDs -- cool, neutral, warm, multiphosphor/high-CRI. In fact, neutral tinted LEDs have the potential to be MORE efficient in lumens/watt than cool white, because the eye has low sensitivity to blue light, which is so dominant in the cool emitters. Many of these already exist, including 3500k warm white Crees with Q2 efficiency and good spectra -- that's still more efficient than ANYTHING a year ago. I suspect many people on these boards would be happier if their lights were loaded up with emitters like that, instead of R2-bin cool emitters. In the not to distant future I plan to go replace a lot of my old cool LED lights with neutral and warm emitters.

Improvements in both the underlying LEDs and phosphor blends will both happen over the next few yeears as there will be a push to make LEDs capable of replacing things like small halogen spotlights, and eventually more general lighting.

I suspect LED tech will eventually approach a 200lm/Watt efficinecy cap for white light with a good spectrum. When that happens, battery technology will really be the only limiting factor. Keychain lights producing several hundred lumens I believe will be a very real possibility.

Theoretically full spectrum white can only be 242.5 lumens per watt. see all those "finally! 300 lumens per watt" threads

That's if you want a continuous spectrum simialr to sunlight. You could cut away most of the violets and a lot of the deep reds, get more like 350lm/W max, and you'd be hard pressed to tell the difference.

I suspect we may see REAL LEDs achieve 70% of theoretical maximum, or about 200lm/W with a VERY good spectrum. How do people like the sounds of a keychain light pumping out several hundred lumens for half an hour?

 

[jtr1962]

Correct me if I'm wrong, but 1000lm/w is far above the physical limit of converting energy into light. It's kind of like wishing for a gasoline internal combustion engine that makes 600hp per liter --it ain't gonna happen.

As mentioned perfect white light is around 240 lm/W but you can get well above 300 lm/W while still having a CRI of 98, and approach 400 lm/W with a CRI in the low 80s (still plenty good enough for all but the most critical color matching). However, these are theoretical numbers. In practice figure about 80% of that, perhaps 90% on the outside. The comparison to hp per liter though makes no sense. There is no inherent theoretical limit to hp per liter given new materials or cooling methods. The existing limits are practical limits. There is an inherent limit to how much energy you'll get out of a mass of any given fuel but that's entirely different.

Battery technology will probably be the limiting factor in the end. I see LEDs of 250 to 300 lm/W within a decade. How long lights using these will run is dependant upon discovering new battery chemistries. NiMH and li-ion both give about the same energy density per unit volume, although li-ion by virtue of its lighter weight gives more per unit mass. The sky's the limit on what new batteries may be capable of. A 5000 mAh AA in a decade wouldn't surprise me. If we can harness cold fusion in a small cell then we're really talking about unlimited runtime. Who really knows what will be ten years from now? When I bought my first 5 mm white LEDs about 8 years ago I suspected in time they would be cheaper and brighter. However, I had no idea we would ever have the high-power LEDs which exist today putting out several hundred lumens.

 

[Frankiarmz]

As mentioned perfect white light is around 240 lm/W but you can get well above 300 lm/W while still having a CRI of 98, and approach 400 lm/W with a CRI in the low 80s (still plenty good enough for all but the most critical color matching). However, these are theoretical numbers. In practice figure about 80% of that, perhaps 90% on the outside. The comparison to hp per liter though makes no sense. There is no inherent theoretical limit to hp per liter given new materials or cooling methods. The existing limits are practical limits. There is an inherent limit to how much energy you'll get out of a mass of any given fuel but that's entirely different.

Battery technology will probably be the limiting factor in the end. I see LEDs of 250 to 300 lm/W within a decade. How long lights using these will run is dependant upon discovering new battery chemistries. NiMH and li-ion both give about the same energy density per unit volume, although li-ion by virtue of its lighter weight gives more per unit mass. The sky's the limit on what new batteries may be capable of. A 5000 mAh AA in a decade wouldn't surprise me. If we can harness cold fusion in a small cell then we're really talking about unlimited runtime. Who really knows what will be ten years from now? When I bought my first 5 mm white LEDs about 8 years ago I suspected in time they would be cheaper and brighter. However, I had no idea we would ever have the high-power LEDs which exist today putting out several hundred lumens.

Great post. Would you agree that interest in both LED's and more advanced batteries is primarily what drives the timeline for the future of these products? Had interest not taken off in the form of "Flashaholics", willing to invest in high end LED flashlights would the industry be where it is today? Just look at digital cameras and mega pixels for example, a very few years ago three to five was a high end offering, now the number is ten or twelve. The manufacturers know that if they can make a brighter, smaller, longer run time LED, we will buy it and that guarantee is all they need.

 

[jtr1962]

Great post. Would you agree that interest in both LED's and more advanced batteries is primarily what drives the timeline for the future of these products.

I agree with this 100%. I'll go so far as to say that flashlights in turn are driving the eventual use of LEDs for general lighting. Many are looking at their LED flashlights, and wondering what else can these things do.

I've observed similar trends elsewhere. For example, interest in first digital photography and then video drove the huge increase in hard disk size. Had everything on the PC remained text-based, a few hundred megabytes would have sufficed. And same thing with processors. More complex software drove the push for ever faster processors. The fact that LED efficiency is exceeding the timeline set forth a few years ago tells me that demand is playing a huge factor. The LED manufacturers know they can sell the next highest binned LEDs as fast as they can make them, so the push is on to get efficiency up as rapidly as possible .

 

[copperfox]

The comparison to hp per liter though makes no sense. There is no inherent theoretical limit ... There is an inherent limit ...

You just contradicted yourself.

I intentionally specified "gasoline internal combustion engine" and you said you agree that a certain fuel has an inherent limit to how much energy you can get out of it. That reinforces my original position.

To clarify: There are physical properties of the materials used in a design that establish an upper limit of possible efficiency. In the engine analogy, the fundamental limiting properties are the potential energy of the gasoline and the burn rate. So no, the upper limit of efficiency of the gasoline ICE are not practical limits (as in: configuration, materials, and losses), they are inherent (as in: unchanging physical property of the gasoline). We have not yet reached this upper limit of efficiency.

 

[Frankiarmz]

You just contradicted yourself.

I intentionally specified "gasoline internal combustion engine" and you said you agree that a certain fuel has an inherent limit to how much energy you can get out of it. That reinforces my original position.

To clarify: There are physical properties of the materials used in a design that establish an upper limit of possible efficiency. In the engine analogy, the fundamental limiting properties are the potential energy of the gasoline and the burn rate. So no, the upper limit of efficiency of the gasoline ICE are not practical limits (as in: configuration, materials, and losses), they are inherent (as in: unchanging physical property of the gasoline). We have not yet reached this upper limit of efficiency.

I disagree with your example of gasoline and maybe my argument is flawed but here it goes. When internal combustion engines used carbs gasoline had not reached it's full potential, but the introduction of fuel injection increased it greatly. The advent of electronic ignition saw more horsepower derived from the same quantity of gasoline. Direct injection, multi valve engines and other technological advancements have proved more and more energy could be derived from the same quantity of gasoline. How can you know with certainty that what we believe to be the limits of potential energy from a given source will not change with technology ?

 

[copperfox]

...Direct injection, multi valve engines and other technological advancements have proved more and more energy could be derived from the same quantity of gasoline.

I agree, but these are examples of changes in the configuration and materials used, etc. in the engine. The gasoline and its respective physical properties remained the same. We are constantly refining the ICE design, but as I already said, we have not yet reached this upper limit of efficiency for gasoline in an internal combustion configuration.

How can you know with certainty that what we believe to be the limits of potential energy from a given source will not change with technology ?

Because of the laws of physics. We don't create more potential energy in a given resource, we simply refine our process of extracting it (i.e conversion efficiency). This goes for coal power plants, combustion engines, and LEDs. In the case of LEDs (to get back on topic) what you are converting is electricity into photons. The LED as a fundamental design will only carry us so far. The reason we are producing more efficient LEDs is because we are moderately clever humans and we make practical changes to the design and implementation of the technology. At some point in the future, however, the physical limit of efficiency of the LED will be reached, and at that point, no amount of tinkering or redesigning will result in more light. Fortunately, with LEDs as with engines, there is still plenty of room for innovation.

 

[CM]

The P7 led is the next step for high power flashlights, it can handle 700+ lumens, depending on battery power and cooling. I.e. it needs rechargables or more than two CR123A batteries.

In a few years the flashlights will be better at showing colors and the leds will have improved efficiency, i.e. the 200+ lumens of today will probably be 400+ lumens.

I don't consider the P7 to be "the next step". It's just a scaling up of current technology by cramming more emitters together in a small space, just like the Lux V was for lumileds. The increase in light output is accompanied (or paid for) by requiring more current, dissipation of more power and if you do the math, less efficiency. 700 lumens would be a lot more interesting if it can be done at 350mA instead of 3A As pointed out above, better color rendering is very much desired if led's are going to be adopted for general purpose lighting beyond flashlights. Right now, everyone is playing the "lumens/watt" game where the P7 actually loses out.

 

[jtr1962]

You just contradicted yourself.

I intentionally specified "gasoline internal combustion engine" and you said you agree that a certain fuel has an inherent limit to how much energy you can get out of it. That reinforces my original position.

To clarify: There are physical properties of the materials used in a design that establish an upper limit of possible efficiency. In the engine analogy, the fundamental limiting properties are the potential energy of the gasoline and the burn rate. So no, the upper limit of efficiency of the gasoline ICE are not practical limits (as in: configuration, materials, and losses), they are inherent (as in: unchanging physical property of the gasoline). We have not yet reached this upper limit of efficiency.

I think here my engineering background is causing a bit of a communication problem because what you wrote can be interpreted two ways. Please let me know which way you meant. I'll explain:

I initially assumed that when you mentioned 600 HP per liter you were referring to a liter of engine displacement. That's what I based the rest of my post on. There is no inherent theoretical limit to how much power you can get per liter of engine displacement. In theory you can make a 1 cc engine which puts out 100,000 HP given the right design and materials but you're still going to have to figure a way to get huge amounts of fuel per unit time into that engine.

Now if you're referring to 600 HP per liter of gasoline, then the units are wrong and it makes no sense. HP is a unit of power, or energy output per unit of time. This is not the same as energy. HP-hour is a unit of energy. HP-hours would be the proper unit to use if that is what you meant, as in you can't get 600 HP-hours per liter of gasoline. 600 HP-hours could be 600 HP for a period of 1 hour, or 300 HP for 2 hours, or 1 HP for 600 hours. It represents a unit of energy, and no matter how clever the engine design you couldn't get more energy out of a liter of gasoline than the potential chemical energy. Point of fact the best engines today get less than 25% of the energy out of gasoline. In theory lots of room for improvement. In practice Carnot's law and the combustion chamber temperature limits due to the melting point of the materials used to build engines will keep the practical efficiency well under 100%. It's an inevitable result of the means by which chemical energy in the fuel is converted to motion. An electric motor on the other hand uses a different process and can in both theory and practice convert 100% of the electrical energy into motion. The best electric motor designs exceed 95%. Batteries in turn convert upwards of 80% of their chemical energy into electricity.

LEDs don't have the practical limits of gasoline engines. In fact, a good analogy is that the LED is to the incandescent lamp as the battery-electric motor is to the gasoline engine. The battery-electric motor combination can easily convert upwards of 80% of the energy stored in the battery into motion because it's not a heat engine. The gasoline engine will be lucky to manage 25% of the energy stored in gasoline for practical reasons. Likewise, the process of photon emission in a semiconductor can in theory be 100% efficient without resorting to the super exotic materials a 100% efficient engine or a 100% efficient incandescent lamp would require. We still won't get there since nothing in this world is 100% efficient, but I think 80% is realistic, 90% a possibility.

In general the efficiency of any process is constrained by both inherent physical limits and the method the process uses. A fuel cell-electric motor can in theory extract more energy from a liter of gasoline than the best piston engine designs because it's using a different process. Same thing with LED versus incandescent. A 6700K filament would be over 90 lm/W but we lack a material which stays solid at that temperature. If we did, and if we coated the lamp with materials to reflect invisible light back to the lamp so we need less power to keep the filament at 6700K, we could in theory have 100% efficient incandescent lamp. Likewise, you could have a 100% efficient engine if you could combust the fuel at millions of degrees, or if your waste heat environment were at absolute zero. In practice none of these possibilities exist, so we look for other means to do the same tasks.

 

[hunter3]

In fact, a good analogy is that the LED is to the incandescent lamp as the battery-electric motor is to the gasoline engine.

:twothumbs jtr1962 = WIN

As far as battery technologies go, the next step seems to be using nanotechnology to improve Li-ion. They've achieved something like 800mah per gram, with extremely rapid charge rates. Within the forseeable future of less than three years, I doubt batteries will improve more than that.

On the other hand, with boost circuitry widely available, what's stopping AAA-sized flashlights from producing 1000+ lumens, even if the runtime is reduced to a few minutes?

 

[jtr1962]

On the other hand, with boost circuitry widely available, what's stopping AAA-sized flashlights from producing 1000+ lumens, even if the runtime is reduced to a few minutes?

Probably LED efficiency is the main problem here. A P7 would need to be powered with about 11 or 12 watts to put out 1000 lumens. I'm not aware of any boost converter small enough to fit into a AAA light which could supply this. On the other hand, if we had a 250 lm/W emitter then you only need 4 watts of power. A small boost converter fitting in a AAA light might only be 80% efficient so you'll need 5 watts from the battery. That's about 4 amps. Some AAA cells can supply this with no problem, albeit only for a few minutes. A 1000 lumen keychain light would be kind of cool actually. People will expect something like a dim 5mm LED. The reaction will they see it putting out as much as a 60 watt incandescent lamp will be priceless. :nana:

 

[HKJ]

I don't consider the P7 to be "the next step".

In my opinion it is in flashlights, but not in led technology. Combining multiple emitters in one package makes it possible to go above the 200-250 lumen flashlight and still have a decent reflector or optic.

Look at the current market, how many commercial led flashlight can your find that is above 250 lumens (Answer: very few)?
My guess is that in the next year we will see a lot of flashlight above 250 lumens, using either the P7 or some other multi emitter led.

 

[copperfox]

I initially assumed that when you mentioned 600 HP per liter you were referring to a liter of engine displacement.

I was.

That's what I based the rest of my post on. There is no inherent theoretical limit to how much power you can get per liter of engine displacement.

As a stand-alone statement, I agree with you. But I anticipated that and so I specified gasoline ICE, to attempt to reduce confusion. It didn't work .

HP is a unit of power, or energy output per unit of time.

Right. And the limiting factor in how much power you can make with that gasoline is it's burn rate, a unit of time. Let's assume that we have a super engine capable of surviving 100,000 rpm. Let's also specify that it is a 4-stroke of wankel configuration. The reason gasoline is critical to my argument is because in theory, the upper limit of revolutions per minute is determined by the burn rate, not the engine's ability to survive high RPM. In reality, the upper RPM limit is probably much lower than 100,000 due to the fact that the piston can only travel from TDC to BDC in an amount of time equal to the air-fuel mixture's maximum burn (explosion) rate.

Point of fact the best engines today get less than 25% of the energy out of gasoline.

Right. The average car engine makes less than 100hp/l, naturally aspirated. Even the car (commercially available) with the highest naturally aspirated power output per liter only makes 120hp/l. I made an extrapolation based on these numbers that if 100% of gasoline's fuel was used that it would be near 500hp/l. I used 600hp/l to give myself some wiggle room. This number is based on some assumptions, and is likely below the true upper limit, mostly because I forgot to factor in forced induction. I realize the analogy wasn't that good.

In general the efficiency of any process is constrained by both inherent physical limits and the method the process uses. A fuel cell-electric motor can in theory extract more energy from a liter of gasoline than the best piston engine designs because it's using a different process.

I agree.

 

[jtr1962]

I understand now what you were trying to say. Obviously there are going to be physical limits to how much HP you can get per liter of displacement. I know that. These are practical limits for the most part, not theoretical limits like the amount of energy you can get from a gallon of gasoline. I guess I was just nitpicking on the point. Yes, a given gasoline-air mixture at a certain pressure has a maximum burn rate. Also, there are limits on how quickly you can exhaust and intake the cylinder. Obviously by running everything at much higher pressures the speed of all these processes can be increased, but then there are practical limits on how high pressures can go. So in theory no limit on HP per liter if pressure and RPM goes to infinity but in practice we both know that can't happen. In other words, I agree with you.

Making a similar analogy to LEDs, HP per liter is analogous to lumens per square millimeter. In theory there is no limit to how intense you can make an LED if you could pump hundreds of amps through a small die. You could in theory get 1 million lumens from a small die without violating any laws of physics. You may need to input thousands of watts of power to do so, but you wouldn't be violating the law of conservation of energy. In practice obviously die resistance and junction saturation will cause output to level off long before current gets that high. Not to mention you'll have the problem of removing a lot of heat from your LED unless it happens to be 100% efficient at converting electricity to light.

On another note, I absolutely love how science fiction writers routinely come up with all sorts of ideas which might be possible in theory, but never in practice. One of my favorites was using a quantum singularity for power. Even if you could bottle such a thing at will, you're left with the practical problem of removing gigawatts of power from something smaller than a neutron. Talk about a difficult heat transfer problem! In light of this, a 1 cc, 100,000 HP engine seems almost tame!

 

[Moat]

... and piezoelectric devices into flashlights to assist with cooling...

Hey... that gives me a (probably silly) idea - why not mount the LED to a heatsink that itself is a thermocouple - thereby converting the otherwise wasted heat energy back into electrical energy - to re-charge the battery, for example. Like re-generative braking on an electric/hybrid car!

Nah, I know... I suppose the heat>electric conversion efficiency of known thermocouples is probably relatively poor, and/or the Voltages produced are in some unuseable range...

Just thinkin' out loud, again -

 

[2xTrinity]

Hey... that gives me a (probably silly) idea - why not mount the LED to a heatsink that itself is a thermocouple - thereby converting the otherwise wasted heat energy back into electrical energy - to re-charge the battery, for example. Like re-generative braking on an electric/hybrid car!

Nah, I know... I suppose the heat>electric conversion efficiency of known thermocouples is probably relatively poor, and/or the Voltages produced are in some unuseable range...

What you're talking about isn't really analogous to regnerative braking, but rather like combined cycle engines, where you use hot exhaust gases from one engine to drive a steam turbine and generate more power. The problem is, if you're generating energy from heat, you inherently need a high temperature differential. Maximum possible efficiency of any engine is determined by the following formula:

Thot / (Thot - Tcold)

For a heatsink, you want the exact opposite -- in a perfect world you want there to be NO temperature difference between your LED and the surface of the light.

The problem is, passive cooling, like slapping LEDs onto a big chunk of coper, won't be able to keep up with the demand for more and more throw (which requires a lot of poer to be pumped through a small area). The problem is most of the active heat dissipation systems have a lot of problems:

1) Fan cooling -- bascially, you throw away all hope of waterproofing your light, and you have a lot of fragile mechanical parts to break should you drop the light.
2) Piezoelectric cooling -- basically, these are power hungry, and would themselves cerate more heat. In a compact system like a flashlight, and not a fan-cooled computer case, they'd probasbly actually worsen the problem.

Basically the only viable solution I cn think of is to use heatpipes -- basically copper pipes with a fluid in them that is designd to evaporate at roughly the operating temp of the LED (by adjusting the pressure insize), then condense elsewhere. A wick then returns the condensed fluid to the "hot" side of the pipe. No input power or moving parts are necessary.

 

[Moat]

The problem is, if you're generating energy from heat, you inherently need a high temperature differential.

Ah... makes perfect sense. Would need a smokin' hot LED to work - the opposite of what we want. Silly it was, then!

Although... how about using the boiling fluid inside a heatpipe to spin a tiny turbine, driving a nano-generator that recharges the battery... :duck:

 

[RustyKnee]

Ah... makes perfect sense. Would need a smokin' hot LED to work - the opposite of what we want. Silly it was, then!

Although... how about using the boiling fluid inside a heatpipe to spin a tiny turbine, driving a nano-generator that recharges the battery... :duck:

Wouldn't that restrict the fluids ability to travel...and therefore the heat dissipating capacity?

The biggest thing for me of increases eficacy is reduce thermal managemnt requirements. Less heat is generated so you can either use "fenix turbo" for longer for a given brightness or get more light for the same heat build up in a small package.


Stu

 

[SemiMan]

I hope the future brings......... no more questions about that the future will bring......... cause it ends up with meaningless drivel and degenarates into debating perpetual motion or something of similar value. What will the future bring:

- LEDS will get more efficient. There is a hundred threads on here that accurately talk about the physical limit to LED efficiency. It is hard and can not be crossed. It is not even one order of magnitude away. Practically, and with white light of a reasonable color, it is only about 3x - 4x absolute maximum away.

- LED surface brightness will go up. Heck, it may go up a lot. There are not the same hard limits on this..... yes any number of things must improve..... current density versus life, phosphor if used, light versus heat, etc., but any hard physical limit is a long way away. Perhaps we will have LED flashlights with the throw of a short arc xenon?

- Batteries will get better. They may actually get much better in the very short future. We may get new power sources as well. Here is an area where there is in no theoretical limit, but expect jumps and then small performance increases.

- Boost/buck circuits will get better in terms of efficiency...but marginally as they are pretty good. They will get smaller and they will become more efficient at low voltages.

- Something may replace LED.


There, how is that for a summary?

 

[Frankiarmz]

I hope the future brings......... no more questions about that the future will bring......... cause it ends up with meaningless drivel and degenarates into debating perpetual motion or something of similar value. What will the future bring:

- LEDS will get more efficient. There is a hundred threads on here that accurately talk about the physical limit to LED efficiency. It is hard and can not be crossed. It is not even one order of magnitude away. Practically, and with white light of a reasonable color, it is only about 3x - 4x absolute maximum away.

- LED surface brightness will go up. Heck, it may go up a lot. There are not the same hard limits on this..... yes any number of things must improve..... current density versus life, phosphor if used, light versus heat, etc., but any hard physical limit is a long way away. Perhaps we will have LED flashlights with the throw of a short arc xenon?

- Batteries will get better. They may actually get much better in the very short future. We may get new power sources as well. Here is an area where there is in no theoretical limit, but expect jumps and then small performance increases.

- Boost/buck circuits will get better in terms of efficiency...but marginally as they are pretty good. They will get smaller and they will become more efficient at low voltages.

- Something may replace LED.


There, how is that for a summary?

I think if anything you've proved that discussion of what the future may bring is thought provoking and worthwhile. You have touched upon many things that deserve more conversation and not less. Thanks.