# Constant Ratio found in various LED/reflectors throw comparison



## kosPap (Apr 7, 2011)

Hi all! Title is telegraphic and does not tell the things exact.

While trying to compare LEDs for their “throw” potential I measured light box lumens and hotspot intensity of them in their respective P60 modules.
LEDs where XR-E, XP-E, XP-G, MC-E, XM-L in their own reflectors.
Since the output was not the same I calculated the ratio of hotspot Lux and lightbox Lux, in essence calculating the Lux per Lumen Ratio of the various combionations

Fast forward yesterday where the throw of the expected Armytek Predator XM-L version was discussed in the Greek flashlight forum.

So I started tinkering with numbers and made new measurements of XP-G & XM-L in a DBS, and XR-E & XM-L in a Solarforce Masterpiece Pro-1 head.

It turns out that the Lux per Lumen Ratio is a formidable tool since results were related and I could calculate throw of a given LED based on the rest of the measurements,even among different LEDs. I even want so far as to try it with Selfbuilt’s measurements of the Lumintop TD-15 & TD-15X, only to get the same phenomenon

At that point I was pretty impressed and elated enough to make my own unit, *Throw Potential (THp)*, which is of course the “Lux per Lumen Ratio in a given reflector”

Even installing my XPG & XML pills in an Aurora V6 that has an XR-E SMO reflector gave results close enough. 





By nighttime this was troubling me, ‘cos I can not possibly be a modern day Einstein making a breakthrow in Flashlight Universe Unification Theory! Obviously! But the repeatedly occurring calculation results hinded a hidden parameter. 

So I proceeded in comparing the “Throw Potentials” of the XPG & XML. BAM!
For the sets of measurements I have, their ratio hovers around 2.5. (see the table above again please). So what this tells us is that the XP-G is 2.5 more throwy than the XM-L in similar reflectors. 

No I do not believe in magic, so this 2.5 factor must be coming from somewhere.
Reflector mathematics are in order, but this is where the journey ends for me!

Your measurements are welcome! 

I hope in your input & insight, Kostas


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## saabluster (Apr 7, 2011)

kosPap said:


> At that point I was pretty impressed and elated enough to make my own unit, *Throw Potential (THp)*, which is of course the “Lux per Lumen Ratio in a given reflector”



I have a migraine right now so I'm not going to go into this too much as it hurts to think but I would say you are off-base. Throw potential has absolutely nothing to do with a reflector or any other collimating device. Throw potential is lumens per surface area squared. Sorry to burst your bubble.


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## gcbryan (Apr 8, 2011)

I don't have a migraine but it hurt my head to read the first post 

Just a few thoughts. Potential is the wrong word to use here. In addition relating (ratio) lux to lumen serves no useful purpose as they aren't related (can't determine one from the other).

Divide lumen output by the size of the emitter surface area and the highest number wins...XR-E is still the winner at rated current as I recall.

The reflector does affect throw but it can't increase the "potential". That comes from the emitter size/surface brightness.

Without making my head hurt  I think what you have going on here is just that it's possible to construct a ratio between any two items.


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## HarryN (Apr 8, 2011)

Hi, I have been playing with power leds and optics / reflectors for only 11 years, so I still learn something new and interesting about them all of the time.

KosPap - I am interested to see a little more about your experimental setup to obtain the core readings, as this will help me understand your result, especially the lux hot spot reading measurements.

I am just guessing here, but the ratio might be coming from a combination of features such as emission angle, surface brightness, etc, which formula down to the 2.5 ratio in the analysis. In any event, it is always fun and interesting to see how people learn from playing with light and try to relate it to math. 

Some optical properties are not intuitive, at least for me. I really struggled for several years with the idea of surface brightness and throw being so strongly related, and spent a lot of money trying to work against this.


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## kosPap (Apr 8, 2011)

well HarryN, my thoughts exactly, this is why is stated "I do not believe in magic, so this 2.5 factor must be coming from somewhere.".....there IS a pattern between XPG & XML throw relationship in *similar* reflectors......
now I am just searching for someone that can explain it why.

Regarding my set up is a standard practice....Lux where measured in my shoe box....they do vary from other members boxes but they ARE repeatable within my set...lux hotspot was measured at 1 meter.....both measurements were taken at 15sec from on, with fresh batteries.

gcbryan & saabluster, why don't you crunch some numbers?

here is some more data, though some differences might occur sicne there are various combinations there (OP & SMO). 







regarding throw potentail, I did not know there was a unit for it already.....so I better coin another term


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## gcbryan (Apr 8, 2011)

How many times bigger is the XM-L die than the XP-G die?

The constant in this whole scenario is that as die size (and lumen) increases the surface brightness stays fairly constant.


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## phantom23 (Apr 9, 2011)

gcbryan said:


> How many times bigger is the XM-L die than the XP-G die?



4 mm^2 (XM-L) vs. 2 mm^2 (XP-G)


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## gcbryan (Apr 9, 2011)

There's your answer.


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## blasterman (Apr 10, 2011)

> Throw potential is lumens per surface area squared. Sorry to burst your bubble


 
Maybe we're thinking different things, but my understanding of the term 'throw' is simply the collimation factor of a given light source *and* optic. I fail to see how just a light source by itself has anything to do with throw. If it's just a matter of squares, than any light source four times brighter than another one has the same throw. Also, to compensate for the larger size of certain new dies like the XM-L you need a larger/deeper reflector to achieve the same collimation angle, correct? Or, is it a given that reflector size *is* a constant....reading above I'm not clear on that.

Light houses in the 1800's didn't exactly have pinpoint high intensity light sources but were capable of pretty darn good throw (dozens of miles) by the basis of having pretty large lenses.


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## gcbryan (Apr 10, 2011)

blasterman said:


> Maybe we're thinking different things, but my understanding of the term 'throw' is simply the collimation factor of a given light source *and* optic. I fail to see how just a light source by itself has anything to do with throw. If it's just a matter of squares, than any light source four times brighter than another one has the same throw. Also, to compensate for the larger size of certain new dies like the XM-L you need a larger/deeper reflector to achieve the same collimation angle, correct? Or, is it a given that reflector size *is* a constant....reading above I'm not clear on that.
> 
> Light houses in the 1800's didn't exactly have pinpoint high intensity light sources but were capable of pretty darn good throw (dozens of miles) by the basis of having pretty large lenses.



The "potential" isn't increased by anything you do after the emitter meaning that you can't make it any brighter than it is at the source with anything that you do. You can do a more effective job of using what you're given at the light source by doing a better job of collimation...larger reflector for example.

A light house in the 1800's with a higher intensity light source than another light house in the 1800's would have had more "potential".

In the example given by the OP the diameter of the reflector was to stay the same size. A larger reflector will always be able to do a more effective job with the light source potential that it is given. You can make a thrower out of a XM-L if you use a reflector that is twice as big. If your example is to use the same reflector you get the scenario in the OP with the 2.something ratio.

I don't know that the OP's question can totally be answered by the size difference but I think it explains most of it. There is another (almost) constant and that is that many of the chips are relatively close to the XR-E at the top of their performance spec...they can handle much more current. So if you slightly overdrive a particular new chip you may get the surface brightness of a XR-E driven within it's much lower specs.

It's what we've all noticed...as each chip comes out they are never as "bright" as we expect because the lux isn't increasing. The increases are coming in the lumen output. The hotspot is larger but it doesn't throw any further (or as far). So there is a sort of constant of surface brightness not improving as lumen output does improve.

On an intuitive level (please correct me if I'm wrong) I think that surface brightness remaining relatively constant and increasing die size being proportional to increasing lumen output is the explanation of the 2.. ratio in the OP. It's not really any connection between lumen and lux since those two concepts aren't related (you can't get one from the other).


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## saabluster (Apr 10, 2011)

blasterman said:


> Maybe we're thinking different things, but my understanding of the term 'throw' is simply the collimation factor of a given light source *and* optic. I fail to see how just a light source by itself has anything to do with throw. If it's just a matter of squares, than any light source four times brighter than another one has the same throw. Also, to compensate for the larger size of certain new dies like the XM-L you need a larger/deeper reflector to achieve the same collimation angle, correct?
> 
> Light houses in the 1800's didn't exactly have pinpoint high intensity light sources but were capable of pretty darn good throw by the basis of having pretty large lenses.


 
It's a good question. To be certain there are different uses of the word throw and thus some subtle variations in definition but he did not use the term throw alone. He said throw potential. Throw potential starts with one basic thing and that is what we have come to call here surface brightness. Everything else branches off of this. 

It is true that for throw to happen it requires both a light source and a method of collimating that light. So why would we say that surface brightness is _more_ important than the collimator? 

Let's take it from two angles. 

First is the simple fact that light is the first thing required in the entire sequence of events. Without the light source nothing after matters one bit. In fact if you strip everything down to the basic elements even a bare bulb can be said to throw light on an object even if the usage of the term there does not follow the more common form. Try as a reflector or lens might it is utterly helpless to produce anything that might be called throw without a light source.

Second is the idea that "potential" brings to the table. It gives the sense of the outer limits of what's possible. Any given type of collimator is given natural bounds to its potential largely by the size of the collimator. Then too there are the bounds placed upon the size of the collimator by the need for something practical. Sure a reflector the size of Jupiter would throw better than the DEFT's lens but it's not terribly portable. There are not as stringent and unchanging bounds placed on surface brightness however. Sure current technology does place some bounds but they continue to loosen as time goes by. I think most rational people who are familiar with the technology can see the day when battery technology and emitter technology will allow levels of current density/surface brightness unthinkable today. 

So since the collimating device can only get so big the real factor that will determine throw is how bright a source you can give that collimator.


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## kosPap (Apr 10, 2011)

saablaster, you are missing this:
"to make my own unit, Throw Potential (THp), which is of course the “Lux per Lumen Ratio *in a given reflector*” 



gcbryan said:


> How many times bigger is the XM-L die than the XP-G die?
> 
> The constant in this whole scenario is that as die size (and lumen) increases the surface brightness stays fairly constant.


 
but there is one more factor when we discuss "throw" L:ED construction and to be specific teh lens on teh substrate....

se the XRE and XPes, same die size, same surface brightness but different beam....

I will have to remind all teh purpose i am dividing hotspot lux by lightbox lux ergo lumens...to even out the difference of LED output since i do not have the means to drive all of them at the exact same OTF lumen output.

Now can anyone explore the notion more by driving, say an XPG & an XML in a mag reflector, at say 250 OTF lumens and then measuring throw? aka Lux at 1m?


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## ma_sha1 (Apr 10, 2011)

My head hurts too, is this Einstein's way of saying if everything being equal, XPG will throw better than XML? 

The XPE has wider beam spread than XRE, in theory, it should throw better than XRE in reflector as more light goes sideways to hit the reflector. In Aspherics, XRE will win as more lights goes toward front. Such difference are due to dome geomnetry, as they have same die size & R2 binning. 

In p60 drop ins, I also noticed some reflector bottom hole is too small & xpe sit too far back & blocked some lights, it might artificially reduced the lumens & thus inflated your lux/lumen ratio. I would not expect that much of difference between XRE/XPE on the ratio. Your light box lumen number is lower on XPE than XRE, which reflects what I observed, i.e. some XPE lumens never made it through the reflector hole.


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## SemiMan (Apr 10, 2011)

Hate to burst your bubble, but lens manufacturers have been using a figure of candela/lumen or lux/lumen at a given distance as long as high powered LEDS and the associated optics have been around. It is somewhat useful to estimate how bright you will illuminate a surface.

Throw potential is really not "potential" but an indication of whether the flashlight will be purely a thrower or have some flood to it. However, that would only work in a reflector where the beam pattern is fairly consistent. With an optic, this goes out the window.

Semiman


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## gcbryan (Apr 10, 2011)

kosPap said:


> saablaster, you are missing this:
> "to make my own unit, Throw Potential (THp), which is of course the “Lux per Lumen Ratio *in a given reflector*”
> 
> 
> ...



I don't think I get the point in all this. The XML die is twice as big as the XPG so if we limited the lumens to 250 the surface brightness of the XPG will be twice that of the XML and it will throw twice as far using the same reflector unless there are major differences in the beam angle of XML vs XPG.


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## kosPap (Apr 11, 2011)

and this is where i predict that it will be 2.5x and not 2x

to me all these are an empirical observation that leads to a tool...

say lets see if the Armytec predator comes over the 13800 lux mark

ma_sha1

indeed....when i got my XPG DBS I did it with the purpose to use the reflector for the SST-50 too...I opened up teh hoel to fir an XRE and I got a 7% increase on the XPG output.....


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## beamis (Apr 29, 2011)

gcbryan said:


> It's not really any connection between lumen and lux since those two concepts aren't related (you can't get one from the other).



They are directly related. One lux is equivalent to one lumen spread out over one square meter. We can use that known relationship to calculate the effectiveness of a light's optics. For example, the TK41 is able to generate a spot intensity of 5175 lux at one meter. That's the equivalent intensity as directing all of the XM-L's 910 emitter lumens onto a circle 24 cm in diameter 1 meter distant.


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