# The details of LED technology?



## Ravana (Feb 14, 2012)

Hey, I'm in the market for my first dedicated flashlight and am attracted to the Foursevens Quark Mini AA2. However, I'm a bit turn off that it's the same model as existed roughly 2 years ago. 

Given that my background is in computers I am used to a field where technology is continuously becoming updated and what is the best today will be outdated tomorrow. 

Even though computers and LEDs are a form of electronics do they have this as a similarity? What I'm asking is if someone could explain or redirect me to something that could explain what exactly is a XP-G R5 and how that differs from a XR-E Q5. Why the XP-G R5 hasn't changed for the last 2 years and if it does does the same technology improve or is replaced by something else. 

In short, someone care to help me clear my flashlight ignorance?

Thanks,
Rav.


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## DM51 (Feb 14, 2012)

Welcome to CPF, Ravana 

We have a separate section for questions about LED emitters. I'm moving your thread there now.


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## csshih (Feb 14, 2012)

Ravana said:


> Hey, I'm in the market for my first dedicated flashlight and am attracted to the Foursevens Quark Mini AA2. However, I'm a bit turn off that it's the same model as existed roughly 2 years ago.
> Given that my background is in computers I am used to a field where technology is continuously becoming updated and what is the best today will be outdated tomorrow.
> Even though computers and LEDs are a form of electronics do they have this as a similarity? What I'm asking is if someone could explain or redirect me to something that could explain what exactly is a XP-G R5 and how that differs from a XR-E Q5. Why the XP-G R5 hasn't changed for the last 2 years and if it does does the same technology improve or is replaced by something else.
> In short, someone care to help me clear my flashlight ignorance?
> ...


 Alright! Let's get you up to speed!
What you're saying has 2 parts. the "XP-G" portion, and then the "R5" portion.

The XP-G is what the entire LED is referred to as. it is a 1.4mmx1.4mm chip in a small 3.45x3.45mm package.
The XR-E, on the other hand, is an older LED. it consists of a 1mmx1mm (or 0.9mmx0.9mm for the newer ones) chip (aka die) in a 7mmx9mm package. see the difference?

Now, the second part of your question. "R5" refers to the LED's efficiency bin. LEDs, when created, aren't all identical due to impurities during creation. As such, they are "binned" (aka sorted) according to their efficiency and even tint (color). The R5 refers to the efficiency (note that efficiency is NOT efficacy, I'll talk about that in a moment)

Back to the R5. In case of the XP-G, that means it makes 139 lumens at 350mA (generally what LEDs are binned at)
Comparing this to your XR-E Q5: 107 lumens at 350mA

However, that isn't all! The forward voltage (Vf) of the emitters is also different!
Now we can get to efficacy! Efficacy, well, Luminous Efficacy, basically defined as lumens per watt. This figure is more important than efficiency, which is usually considered as just the LED(aka emitter) bin.

In your case of XP-G R5 vs XR-E Q5(I'll be comparing them at 350mA):

The XR-E Q5 produces 107 lumens @ 350mA, with a forward voltage of 3.3V
in comparison, 
The XP-G R5 produces 139 lumens @ 350mA, with a forward voltage of 3V!

The XP-G Has a smaller package, produces more lumens at the same current, and has even higher efficacy!

How higher? 132.4 LM/W (lumens/watt) vs 92.6 LM/W!

Now, how much more power does the XR-E consume than the XP-G? 1.155W compared to 1.05 W - and it has less output!

How's that for an upgrade? 

Numbers wise, that's not bad at all, but most of us are human, we have to apply something called the inverse square law - we do not see light increases as linear, we see them logarithmically.
I.E. for a flashlight to be visually 2x brighter to our eyes, it has to actually be 4x brighter. The difference isn't as noticeable!

If you're still reading this, I'd like to add some more information!
LED efficacy tends to drop the higher current you drive them out - they have diminishing returns, but let's compare the XP-G R5 to a XR-E Q5, this time, at 1Amp! (many flashlights drive them this high)

The XR-E Q5 produces 235.4 lumens @ 1000mA, with a forward voltage of 3.7V
in comparison, 
The XP-G R5 produces 347.7 lumens @ 1000mA, with a forward voltage of 3.397V!

The XP-G is 102.4LM/W @1A, and the XR-E is 63.6LM/W @ 1A

Now, how much more power does the XR-E consume than the XP-G? 3.7W compared to 3.397 W - and it has less output!

Another popular emitter is the XM-L - it has a slightly larger package and a much larger die (2mmx2mm!)
That one does 388 lumens at 1 amp, 12.9.3 LM/W, has a 3V Vf, and consumes 3W! even lower than the XP-G, but it has a larger die than the XP-G, allowing for more efficacy.

Another point! The XR-E is rated to 1amp, the XP-G is rated to 1.5amps, and the XM-L is rated to 3 amp!
each of these emitters have a lower thermal resistance than the next, making them quite easy to heatsink. How's that for upgrading technology?

have a look at the XT-E and XB-D for budding technology. The XT-E is the same package size as the XP-G, but offers even more improvements in efficacy! The XB-D is even smaller than the XP-G, but still has a similar output!

Now, for a quick reference, here's the order in which tech was released.

XR-E(the original "big package!), XP-E(shrinking the XR-E!), XP-G(XP-E, but with a larger die!), XM-L(big package with a huge die!), XT-E(going back to the XP-E and improving efficacy!), XB-D(shrinking the XP-E package while retaining efficacy!) (not including lower cost emitters)

Hope this helped 

Craig

PS: cool pix here http://www.candlepowerforums.com/vb/showthread.php?270419 I've been meaning to update the thread with better organization. haven't found time to, lately!


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## AnAppleSnail (Feb 14, 2012)

The short version is:
LEDs are frequently updated, like many chip-based technologies. But a flashlight has limits: Power, interface, and size. The power is defined by the batteries (size-limited too), the interface by programming and interactions (click here, twist there, lick that), and the size by convenience. It isn't hard to program various UIs, so there aren't many huge leaps and bounds there.

The 'effect' of a flashlight is its light. Upgrading an LED one notch isn't as much benefit as with a computer. A light source has to have 40% more output to look a bit brighter, 2x the output to look a noticeably brighter, 4x more to look 'twice as bright.' And we already can put enough lumens in your pocket to make you happy for 99% of uses.

The Quark will make you happy. It is a tool, not a showboat - You could spend the same ~$70 and get a 2000-lumen big-darn spotlight that blinds innocents a mile distant. But the Quark has a 10-year warranty, decent quality, and mine has stood up to a lot of use. Get the quark, or the zebralight, or the fenix, and you won't be disappointed. The piddling upgrades every few years aren't so significant. To get the same features and be "WOW!" brighter, we'd need LEDs that produce 139*4 lumens per watt, and that may be beyond 100% thermodynamic efficiency.


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## csshih (Feb 14, 2012)

AnAppleSnail said:


> The short version is:
> LEDs are frequently updated, like many chip-based technologies. But a flashlight has limits: Power, interface, and size. The power is defined by the batteries (size-limited too), the interface by programming and interactions (click here, twist there, lick that), and the size by convenience. It isn't hard to program various UIs, so there aren't many huge leaps and bounds there.
> 
> The 'effect' of a flashlight is its light. Upgrading an LED one notch isn't as much benefit as with a computer. A light source has to have 40% more output to look a bit brighter, 2x the output to look a noticeably brighter, 4x more to look 'twice as bright.' And we already can put enough lumens in your pocket to make you happy for 99% of uses.
> ...



Thank you for that! it seems when I'm lacking sleep I get giddy and long winded - A strange combination which makes me use a lot of exclamation points.

C


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## Kinnza (Feb 14, 2012)

LED technology involves several factors and you must be aware they improve at different rate.

LED's heart is the chip inside. Chips are improving continously, as you can see for the rising bin for each model. Semiconductor with lower defect density has increased light emission at lower voltage, thus efficiency is greatly improved.

But LEDs are a package which is more than the chip inside. The function of the packege is protect the chip, get as much emitted light out the package and provide an effective means to get ride of the heat generated. Each LED platform achieves all these by different means and once a full package is designed, its lifetime is larger than the chips, which are evolving continously.

For example, with Cree you have different platforms with a defined way of thermal and optical management: XR, XP, XM, XB, XT, MT.... They uses different chips inside along their life, and you can see it for the letter after the platform name:

For example, you have the XP package in the models XP-C, XP-E and XP-G. Those letters refers to the type of chip used. It varies in size (for example, between C and E) or in more things (texturing, current spreaders, and many things more) which often are upgraded by the manyfacturers without a change of the designing letter because improvement affects all the range and replace the previous chip. The consequence is same LED models, as for example an XP-E is going offered each time on higher flux bins (light emission at a given current) and lower forward voltage bins.

There are many improvements introduced by the manufacturers, but which affects only some models or allows to new models, as the improvements might not be general, but offer only an advantage on some applications: remote phosphors, very big chips, and so on.

So actually, LEDs are accomplishing Heitz's law, the equivalent to Moore's law for computers, since 10 years ago (doble performance/cost each 18 months). As with computers, most people are not aware of the ways that improvement is achieved. Mainly on chips, but too upgrading the architecture and other things (as bus speed, memory's speed, etc). People only want faster and more powerfull computers each time for cheaper. With LEDs is the same, people wants each time LEDs more powerfull, with higher efficacy, for cheaper, and the fact is industry is managing to do it. But there is a low degree of standarization that makes it somewaht difficult to notice.

The same lantern than 2 years ago but with newer cmponents usually offer increased more light emission with longer autonomy. Only seems the same lantern for the external body. Similar to you upgrading your computer by changing the mother board and processor, but keeping the case and peripherals the same. People won't notice the difference just by looking at it. But you will notice it when on use.


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## Ravana (Feb 14, 2012)

Thank you all for the detailed responses. Although I'll probably have to do a bit more research to completely understand everything mentioned (or maybe get more than 4 hours of sleep) I did pick up the general gist of it.

I'll be ordering my Quark Mini sometime soon for sure with that worry out of the way.

Thanks again,
Rav


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## RoGuE_StreaK (Feb 14, 2012)

Taking the computer analogue, consider the case of overclocking; yeah, you can get the CPU to run a hell of a lot quicker, but it'll also run a hell of a lot hotter! So unless you've got a water-cooler and peltier strapped to that sucker, it's gonna burn. And you also aren't carrying it in your hand.


csshih said:


> The XP-G R5 produces 139 lumens @ 350mA, with a forward voltage of 3V!


The XM-L, for instance, can be driven @ 3Amps (and beyond!), forward voltage of about 3.35V, so about 10W, giving an "OMG MY EYEBALLS" 850-odd lumens. But how do you design an active heatsink that can dissipate that heat, in a hand-held device, so the body of the device stays at least within holdable temperatures?
So you are stuck down in the lower levels of drive currents for everyday use, which though, as indicated, there are marked increases in the efficacy, due to the inverse square law, it takes quite a lot of increase for this brightness to be apparent.
But if you want to do a short-burst blast of retina-searing light, modern LEDs can deliver, it's the excess heat that's the issue. Give it a few years and 800+ lumens (about a 60W lightbulb) at tolerable temps will be the norm.


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## BvanderG (Feb 24, 2012)

RoGuE_StreaK said:


> The XM-L, for instance, can be driven @ 3Amps (and beyond!), forward voltage of about 3.35V, so about 10W, giving an "OMG MY EYEBALLS" 850-odd lumens. But how do you design an active heatsink that can dissipate that heat, in a hand-held device, so the body of the device stays at least within holdable temperatures?


Holdable temperatures wouldn't worry me too much. In the end the electrical power is just 10W, of which about 2.5W is emitted as light, so your torch gets about 7.5W. Compare that to a traditional torch with a little 25W bulb, of which 23.5W must be led away by heat conduction -- that never gets too hot to hold.
You do need a heatpipe to get the heat away from the little LED fast enough.


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## AnAppleSnail (Feb 24, 2012)

BvanderG said:


> Compare that to a traditional torch with a little 25W bulb, of which 23.5W must be led away by heat conduction -- that never gets too hot to hold.


It doesn't all go into the torch body. Hold your hand in front of a traditional 25W torch. My homebuilt one (metal cup holding a 25W bulb) blasts most of the heat out the front - metal reflects IR too. Of course, on super-high-power ones you'll cook the batteries from conducted heat, but per-charge runtimes over 25 minutes are rare on these lights.


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## BvanderG (Feb 24, 2012)

AnAppleSnail said:


> It doesn't all go into the torch body. Hold your hand in front of a traditional 25W torch. My homebuilt one (metal cup holding a 25W bulb) blasts most of the heat out the front - metal reflects IR too. Of course, on super-high-power ones you'll cook the batteries from conducted heat, but per-charge runtimes over 25 minutes are rare on these lights.


Agreed, but if you consider the order of magnitude and the fact that batteries heat themselves up too, you must conclude that a torch's body can easily conduct 7.5W away without getting very hot.


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## dinac (Feb 24, 2012)

OMG, thnx !
i am looking for this informations all over the internet !


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## yifu (Feb 25, 2012)

Emitter information can be had using the search function but i'll list the basics of each emitter.
XR-E: The P4 pretty much started the LED revolution, with a package that deliver in excess of 100 lumens 5 years ago. Now the top bin is the R2 and is capable of a maximum of 300 LED lumens, existing in either cheaper lights or the very best aspheric throwers like the DEFT.
XP-E: Similar efficiency as the XR-E but with a much smaller package, although the viewing angle is wider. Max is 350 lumens. Rarely used now. Top bin is R4
XP-G: Top bin is S3. Same package size as the XP-E but a larger die area, even larger viewing angle. Max is 493 lumens for the S2 bin.
XM-L: Top bin is the U2, most efficient mass produced LED in the market today. Twice the die area as the XP-G, max is around 970 LED lumens but can be overdriven to produce just a little over 1000 lumens.
Of course, Cree produces a lot more but a lot of them like the XP-C, XR-C, XB-D etc are derivatives and the four above are the main ones.

Other than Cree, there is Nichia (the 119 high CRI LEDs are nice but they dont have a lot of high powered LEDs), Luxeon (Rebel series are used in some lights), Luminous Devices- SST50 (1200 LED lumens at 6A), SST90 (4000 LED lumens for the top WN bin) and then there is the CSM360 (4 SST90 dies) etc.


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## yifu (Feb 25, 2012)

The thing about lighting technologies is that they are very mature and leave little room for further improvement based on current designs, similar to the state of the internal combustion engine. The oldest electrical light source for example is the carbon arc light, over 200 years old and the efficiency still virtually remains the same, at 16-30 lumens/w despite 200 years. Incandescents have only evolved in terms of the fill gases but the efficiencies has remained at the 16-40 lumen/watt mark for decades. HIDs also, have not improved much if at all through the years. Despite power LEDs being a relatively new light source (only 10 years), they have recently approached the 200 lumen/watt efficiency that is the max allowed by current semiconductors (blue light exciting phosphor).
There is a maximum allowed efficiency for light source-683lumens/watt, which makes LEDs 20% efficient.


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## idleprocess (Feb 25, 2012)

yifu said:


> The thing about lighting technologies is that they are very mature and leave little room for further improvement based on current designs, similar to the state of the internal combustion engine.


Automakers continue to engineer the internal combustion engine because they keep realizing cost/performance/efficiency gains from it. Every few years has seen improvements in engine performance - it's other factors (improved crash-worthiness, stricter pollution standards) that slow the realization of these improvements.



yifu said:


> The oldest electrical light source for example is the carbon arc light, over 200 years old and the efficiency still virtually remains the same, at 16-30 lumens/w despite 200 years.


I'm not aware of any serious efforts to improve the carbon-arc light in the last 50 years - its present use seems to be limited to enormous spotlights used to attract attention where raw lumens is key and 16-30 lm/W is acceptable.



yifu said:


> Incandescents have only evolved in terms of the fill gases but the efficiencies has remained at the 16-40 lumen/watt mark for decades. HIDs also, have not improved much if at all through the years.


Incandescents are designed to be cheap first and foremost, thus their efficiency penalty. There are a few tricks in the bag that the manufacturers are experimenting with (such as IR reflective glass and some tricks to improve photon extraction from the filament), but those have not yielded the enormous efficiency gains that LED has seen in recent years.

I gather that arc technologies such as HID, metal halide, sodium-arc, and florescent are already operating close to their maximum theoretical efficiency.



yifu said:


> Despite power LEDs being a relatively new light source (only 10 years), they have recently approached the 200 lumen/watt efficiency that is the max allowed by current semiconductors (blue light exciting phosphor).
> There is a maximum allowed efficiency for light source-683lumens/watt, which makes LEDs 20% efficient.



Yes, but 200 lumens/watt from a low-voltage DC device that can be physically quite small and realize that efficiency across a broad spectrum of gross power dissipations is really something. All of our other lighting technologies have sizable minimum power ratings before they start to operate near peak efficiency; with LED the minimum requirement for peak efficiency is minuscule and the drop off in efficiency from that peak is fairly moderate. High fixture output is largely achieved through parallelism rather than scaling up the device, allowing individual emitters to operate fairly efficiently in terms of lm/W as well as lm/$.


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## idleprocess (Feb 25, 2012)

duplicate


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## pretmetled (Feb 25, 2012)

yifu said:


> Despite power LEDs being a relatively new light source (only 10 years), they have recently approached the 200 lumen/watt efficiency that is the max allowed by current semiconductors (blue light exciting phosphor).
> There is a maximum allowed efficiency for light source-683lumens/watt, which makes LEDs 20% efficient.



Mmmmh? I would think a led that does 200 lumens/watt of WHITE light is ever so slightly more than 20% efficient. I don't know how you arrived at that 20% BTW. For the sake of a simple example, lets assume that this 200 lumens/Watt led was a purely green led bang on target on the 555 nm line. In that case if I'm not mistaken that 200 lumens/Watt would make that green led about 29% efficient. If not what am I missing?

However for a white led you'll have to integrate that luminous intensity thingy over it's entire emitted spectrum. A LED that perfectly and with 100% efficiency generates a black body radiation spectrum of any given temperature will have a number of lumens per Watt that's quite a bit lower than 683. It's sooner in the 260-ish lumens/Watt range. I did a quick octave script the other day but I'll be b***ered if I can find it.

Lazy. Google. From http://forum.onlineconversion.com/archive/index.php?t-7179.html

400-700 nm portions of blackbody radiation at a few color temperatures:

3000 K: 256 lumens/watt
3400 K: 262 lumens/watt
3600-4100 K: 263 lumens/watt, within 1 lumen/watt.
4500 K: 261 lumens/watt
5000 K: 258 lumens/watt
5500 K: 254 lumens/watt
6500 K: 246 lumens/watt

Yup, that's the sort of numbers I got as well. So assuming 263 lumens/Watt of 400-700 nm truncated spectrum that 200 lumens/Watt led is then more like 76% "efficient". The moment you start modulating your spectrum with "ooooh this here wavelenght is more _special_ *(*)* than the other one" you get all sorts of crap where things like "efficiency" get murky IMO. 

*(*)* And that is precisely what the standard luminosity function does.

At best you can pick a given spectrum and then say how efficient your emitter is at radiating that spectrum... Or just take wall power Watts input, and measure total radiated optical output in Watts, and then calculate efficiency. That lumens crap doesn't make the effiency definition any clearer. As said, at best you can say how efficient the emitter is at giving a spectrum. Whatever that spectrum may be, doesn't have to be black body per se.


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## slebans (Feb 25, 2012)

pretmetled said:


> Mmmmh? I would think a led that does 200 lumens/watt of WHITE light is ever so slightly more than 20% efficient.



We've discussed this issue -in detail- several times over the past year. Here are three relevant threads:

http://www.candlepowerforums.com/vb...40-efficient-how-many-lumens-per-watt-is-that

http://www.candlepowerforums.com/vb/showthread.php?311740-LEDs-waste-75-as-heat

http://www.candlepowerforums.com/vb...rical-efficiency-(watts-gt-photons)-of-an-LED

Stephen Lebans


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## yifu (Feb 27, 2012)

Cree broke the 200 lumen/watt mark 2 years ago when they build a 208 lumen/watt LED at 4579K(warm white), amazing!! So my guess is that they would probably release a 200 lumen/watt LED next year and further efficiency improvements would taper down. They seem to be more concerned with low cost LEDs and LEDs that require very little heatsinking, given the release of the XB-D, the XT-E, which are low cost and are binned at 85 degrees celsius instead of the customary 25 degrees celcius. It seems they are now actively targeting the lighting market, instead of the backlight/indicator LED market, where most of the LEDs go (every computer screen, mobile phone has some form of LED backlight.


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## idleprocess (Feb 27, 2012)

yifu said:


> Cree broke the 200 lumen/watt mark 2 years ago when they build a 208 lumen/watt LED at 4579K(warm white), amazing!! So my guess is that they would probably release a 200 lumen/watt LED next year and further efficiency improvements would taper down. They seem to be more concerned with low cost LEDs and LEDs that require very little heatsinking, given the release of the XB-D, the XT-E, which are low cost and are binned at 85 degrees celsius instead of the customary 25 degrees celcius. It seems they are now actively targeting the lighting market, instead of the backlight/indicator LED market, where most of the LEDs go (every computer screen, mobile phone has some form of LED backlight.



Cree appears to be going to where they think the growth will be. Given the traditional lack of thermal consideration in the general lighting industry relative to LED thermal envelopes, it's no surprise that Cree is tackling high temperatures in their new products. Even at 200 lm/W, LED's will probably be deployed in arrays of high single or low double-digit numbers for general lighting, leaving little room for singlular high-performance cost-is-no-object LED's (unlike the flashlight market).

The indicator and small-LCD backlighting markets appear to be dominated by low-cost manufacturers that make money on volume producing mature, near-commodity products. Even if the products are sufficiently differentiated as to make swapping difficult, the relatively short lifespan (on store shelves) of most products with small LCD's makes everyone compete on price since a new model can be fairly easily designed for someone else's SMD LED.

Until recently, most flatscreen monitors and TV's were backlit with CCFL (Cold Cathode FLorescent).


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