Some future prospects of hipo leds

[Nereus]

So far we have seen that lumens/led has been driven up the development in lumens/watt figures. But there is (highly theoretical of course) upper limit for this development of course, 100% efficient led. Approaching this limit may bring some new phenomena to the led modding arena - here is my guess what we may be seeing in future.

Now the upper limit how much one emitter can take input power is pretty much set by its ability to dissipate heat. For example Lux3 can handle 3 watts of heat or maybe a bit more, but it is the maximum heat that sets the upper limit for input power. When lm/w figures increase one input watt produces less heat. Hence, we can dump more power to the led - and get more lumens out of it.

I guess that in future lm/led figure will be driven more by the ability to dump more power to the led rather than lm/w figure itself. When closing the 100% barrier very smal increases in lm/w lead to major increases in lm/led. Why? I can illustrate this with an example: let's assume that some led is 80% efficient. Then some manufacturer introduces 90% efficient led - not a big increase lm/w wise. But what has happened to the heat generated? It has dropped by 50%. What does this mean? We can double the power input of the led because the heat is still the major limiting factor here. The end result is that with a very small increase in lm/w figure it has been possible to double the lm/led figure. Here I am of course assuming that leds are driven all the time to the maximum limit when it comes to heat - but that is what we CPFers do all the time... 😀

So, even though lm/w figures may start to settle and there will be only slight improvements on that area, we will be seeing major increases in lm/led figures.

Ok, let's still focus on my example above. Now assume that there is a very small failure in our 90% efficient led and we are driving it at max when it comes to heat. Let's say that this failure does not brake the led but drops its efficiency down to 80%. What happens now? The heat generated is doubled and the led is boiling! Going from 90 to 80 lm/w is so small change lm wise that you can not see it but it is very fatal when it comes to heat generation. This is a problem that we may be facing in future - the closer we get to 100% efficient leds the more severe it is. We may have to use constant temperature power sources* instead of constant current power sources.

So thanks for reading, feel free to agree and disagree 🙂

-N

*Maglite is industry leader in this arena with its led series...

 

[2xTrinity]

Ok, let's still focus on my example above. Now assume that there is a very small failure in our 90% efficient led and we are driving it at max when it comes to heat. Let's say that this failure does not brake the led but drops its efficiency down to 80%. What happens now? The heat generated is doubled and the led is boiling! Going from 90 to 80 lm/w is so small change lm wise that you can not see it but it is very fatal when it comes to heat generation. This is a problem that we may be facing in future - the closer we get to 100% efficient leds the more severe it is. We may have to use constant temperature power sources* instead of constant current power sources.

Well, that problem is not too difficut to solve, it should simply be a matter of implementing a sense thermistor similar to what the MagLED drop in module uses -- as the LED heats up, the resistance on that component will change, causing the circuit to reduce the driving current.

This will become especially important if they try to sell drop-in replacement LED modules for light bulbs similar to CFLs. If someone were to try to run one of those in a recessed insulated ceiling fixture, they could fry the LED in a matter of minutes (this is the reason why CFLs designed to run in those applications take 2 minutes to reach full brightness -- the phosphor components are designed to operate at a much higher temp so it requires warm up).

Anyway, that's one of the reasons why I hope to see the focus shift toward selling affordable LED fixtures rather than just retrofit replacements, which will likely have problems due to heat management issues.

 

[Xygen]

Ok. One question: How many lumen/watt can we expect from a 100% efficient LED?
I guess around 500 lm/watt. Could that be correct?

 

[Xygen]

Found it: 683 lm/w at 555nm wavelength
Here and here
Nice! The future is bright!

 

[Xygen]

Found it: 683 lm/w at 555nm wavelength
Here and here
Nice! The future is bright!

 

[Curious_character]

But what if we want a white LED? 555 nm is green, and who besides traffic light manufacturers is interested in a super efficient green LED?

c_c

 

[Xygen]

But what if we want a white LED? 555 nm is green, and who besides traffic light manufacturers is interested in a super efficient green LED?c_c

Can't tell you what this 555nm is about...
But regarding you second question: What about a flashlight the size of a Fenix L1x putting out up to 600 lumen, running a few hours and doesn't heat up?
Or a small 100 Lumen flashlight that runs weeks or month on ONE AAA-cell?

 

[Xygen]

Ooops! I missed the word "green".
I don't think this 555nm thing doesn't mean that only green lights can reach 683lm/w. I think it's got something to do that "Lumen" does not cover all light, but only the light that is visible to human eye.
Perhaps someone else can clarify?

 

[2xTrinity]

Ooops! I missed the word "green".
I don't think this 555nm thing doesn't mean that only green lights can reach 683lm/w. I think it's got something to do that "Lumen" does not cover all light, but only the light that is visible to human eye.
Perhaps someone else can clarify?

Actually it does mean exactly that. Lumens are defined in terms of Watts multiplied by how sensitive the eye is to a certain wavelength. A 100% efficient 1 watt IR LED will produce exactly zero lumens, as the eye has zero sensitivity there. At 555nm, the sensitivity peak, a 100% efficient 1 watt LED will produce 683 lumens.

This is the reason why incandescent light have very poor efficiency even though they radaiate almost 100% of their energy -- most of that radiation is IR (zero sensitivity) or deep red (very low sensitivity). They make great electric heaters though.

This is also the reason why sodium lights produce so many lumens per watt -- they produce a yellow color that is near this sensitivity peak, so they will look brighter than the same amount of energy (output) from of a white light. This does not mean they are necessarily more efficient in practical use though -- as a dimmer white light is usually much more useful to actually see by.

Some others have posted on here that the theoretical maximum efficacy of a blue LED plus phosphor (what "white" LEDs now are) is around 330 lm/W. Practially it will probably top out at 2/3rds of that. If you decided to do an emitter that used a separate red, green, and blue die (similar to the pixels on on a jumbotron screen) with 100% efficient LEDs, you could push 400 lumens per watt and we might be able to get closer to that as we don't have conversion losses in the phosphor -- if you wanted any higher than that and you would have to make it look very greenish.

 

[Xygen]

blue LED plus phosphor (what "white" LEDs now are)

Thanks a lot! That is very interesting! I asked myself: What about white LEDs? Didn't knew they are actually blue ones.
:twothumbs