# LED Surface Brightness Question



## gcbryan (Mar 9, 2010)

As new Led's come out XP-G, SST 50 and 90 for example what is changing exactly?

For instance a XR-E has a certain surface brightness. A XPG has a larger surface area but it's not quite as bright.

How does a SST90 compare. I know its surface area and therefore hotspot is larger but is its surface brightness as great or greater than that of a XR-E?

Of course I'm talking about it in a flashlight with everything else the same.

I'm not clear as to whether with current technology it's possible for any led to have greater surface brightness than the XR-E.


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## gcbryan (Mar 9, 2010)

If it turns out that the SST 90 does indeed have a greater surface brightness than the XR-E then to cut to the chase to the question (raised in another thread) regarding throw then this is the reason for the excellent throw with Olights SST90 model.

Throw meaning how far a light can be seen by the eye (normal vision no scope involved) is determined by surface brightness, diameter of the optic or reflector (with a greater diameter being better) and how close the optic is to the emitter (focal length) with closer being better.

So if two flashlights have the same diameter aspheric with the same focal length and one uses the XR-E and one uses the SST 90 the SST-90 will out throw the XR-E not because of greater lumen output but simply because of greater surface brightness (if the SST90 has a greater surface brightness).

So...does it? 

I can't check the various data sheets as they are all .pdf format and my older operating system seems to crash even time I try to read those files.


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## Paul Baldwin (Mar 9, 2010)

Hi, I'd like to know the anwser to this question too as I'm thinking of using one in my projector project.
If it helps your research can I suggest trying to use Foxit free reader to open pdf files. http://www.foxitsoftware.com/pdf/reader/reader3.php My pc isn't exactly new and it copes with this perfectly, as opposed to adobe 

Edit. I think the info you are looking for is in this thread https://www.candlepowerforums.com/threads/261915&page=3 Saabluster is the resident guru in these matters


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## bshanahan14rulz (Mar 9, 2010)

Also keep in mind, it's harder to see the distance when closer stuff is lit up too. Small hotspot contributes greatly to throw. 

If you had a friend go out to your target and you shined the SST and XR-E, both with the same surface brightness and aspheric, your friend would see the same brightness light on the target, just bigger or smaller in proportion to the die.

Good question on which LED has the highest surface brightness, though... XR-E might still be pretty far up there. High output with a small die size and a smaller image.


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## gcbryan (Mar 9, 2010)

I found the answer on SAAbluster's thread. I was trying to stay away from that one as he doesn't want questions on that one. He does now have the answer to my question there however.

The surface brightness of the XR-E is still slightly greater than that of the SST-90.

The SST-90 would have a larger spot of course and therefore be more useful in many cases.


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## Linger (Mar 9, 2010)

gcbryan,
Impressed you made a thread for this, and how quickly it got you an answer. Well done.
There are a number of additional variables, leds are not digital, they do not have a simple 'surface brightness.' Power supply and heat are the key determinants, suggesting that an underdriven overheated xr-e is going to perform much poorer than an over-driven super-cooled xr-e. This gets important to you as a diver in that you can eek some performance gains out of your lights that land led users couldn't dream of if you can take advantage of that great big heatsink you'd be swimming in.

If you haven't checked jtr's white led testing, around pg 14 Harry N asked for a 60degree test of a K2tffc. Jtr performs it, and later in the discussion shows the hypothetical adjustment that can be made showing the expected effects of heat increase. You could push the graph the other direction with excellent thermal pathing.


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## JaguarDave-in-Oz (Mar 9, 2010)

I too will ask my question in this thread and not the other less friendly one.

Much seems to have been made of one emitter having "higher surface brightness" than another newer one but from what I've read, the way that the led is driven will determined how much surface brightness it has (up to the maximum level it can cope with, I guess) and if this is the case then would it not be true that in theory a larger led that just happened to be capable of being driven much harder could concievably have a higher surface brightness than the smaller much vaunted earlier version (I think XR-E)?

If yes, does that mean that brute force (ie driving a more modern more efficient larger led harder) might indeed create more "throw" than a smaller one driven to its lower maximum?


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## gcbryan (Mar 9, 2010)

JaguarDave-in-Oz said:


> I too will ask my question in this thread and not the other less friendly one.
> 
> Much seems to have been made of one emitter having "higher surface brightness" than another newer one but from what I've read, the way that the led is driven will determined how much surface brightness it has (up to the maximum level it can cope with, I guess) and if this is the case then would it not be true that in theory a larger led that just happened to be capable of being driven much harder could concievably have a higher surface brightness than the smaller much vaunted earlier version (I think XR-E)?
> 
> If yes, does that mean that brute force (ie driving a more modern more efficient larger led harder) might indeed create more "throw" than a smaller one driven to its lower maximum?



The answer is that Cree emitters can typically handle overdriving as well as anyone so the XR-E is still likely to be the winner if everything else is the same.

It turns out it's just the size of the emitter divided by it's lumen output. Overdriving increases the lumen output and the size stays the same of course. Cooling makes a certain level of output more sustainable that some design that isn't able to be cooled effectively.

So, it's always possible that a particular design using something other than a XR-E could out throw an XR-E in a poorer design.

As the SST-90 shows however, you can currently get close to an XR-E in throw and have a larger and potentially more useful hotspot with that throw.


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## gcbryan (Mar 9, 2010)

By the way, I've all for that other thread but it sure got off to a bad start. If you're going to explain throw you should do it rather than draw things out for days on end.

If you understand throw you should be able to explain it in a couple of paragraphs. If you later want to go back and add more time consuming aspects such as beamshots that can be done with the edit button.

The much earlier thread with RA that went on for 14 pages made a similar mistake. Long complicated examples before first specifically stating what throw is and what exactly are the variable...then you explain or use examples.


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## JaguarDave-in-Oz (Mar 9, 2010)

gcbryan said:


> first specifically stating what throw is and what exactly are the variable...then you explain or use examples.


I'm still waiting for their definition of throw to see if it is anything like my own personal definition which is simply the distance at which a particular torch can illiminate a dark target at a distance well enough to identify it wiht my set of eyes. I suspect that this forum's definition is going to be nothing even barely related to mine and that I am never ever going to see a measurement standard that will help me make that assessment when it comes to buying a new torch..........


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## JaguarDave-in-Oz (Mar 9, 2010)

gcbryan said:


> The answer is that Cree emitters can typically handle overdriving as well as anyone so the XR-E is still likely to be the winner if everything else is the same.


ok but in real life from brand to brand everything else is never the same and to my layman's eyes some XR-E torches that are driven less hard are sometimes better throwers than other brands with XR-E's driven harder (and thus with apparently more surface brightness). 

In fact a torch that uses a led at a particular surface brightness can throw heaps better than itself using the same surface brightness - Doesn't sound like it makes much sense does it but my P7 Led lenser fits this bill when shifted from full focus to flood setting. Same surface brightness, different throw.

So what determines the throw? Not just surface brightness obviously. 

(as you can tell I'm clueless and couldn't actually follow much of the convoluted stuff written in that other thread so I gave up).


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## gcbryan (Mar 9, 2010)

How that brightness is focused also determines the throw. You could take a light with a XR-E and just take the reflector out and now you would have all flood and very little throw even though the emitter surface brightness would be the same.

Especially with the XR-E an aspheric lens is effective because the XR-E beam angle is 90 degrees and a lot of it just goes straight out without hitting the reflector. This is just spill. When you use an aspheric with such an emitter you focus that light that was just going straight out and your throw increases.

When you do that with a XP-G it's not the same since the beam angle of that emitter is 125 degrees (or something like that) and there isn't a big improvement in throw with an aspheric.

If you're using an optic it also depends on where it is placed. If the focal length is such that you can place it close to the emitter then it's more effective than if it's an optic with a focal length further away from the emittter.

I have one of the DX flood to throw lights using a XR-E. It has a good flood and then throws pretty far as well when you move the head to the throw position. However throw on this light is when the head is pulled away from the emitter. I'm sure that it would throw even further if the optic was in the throw position when it was closer to the emitter as it would capture more light.

I'm looking to see if I can learn anything new from that other thread if it ever gets completed but it was taking too long so I thought those who want to discuss throw now can at least have a place to do it.


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## gcbryan (Mar 9, 2010)

JaguarDave-in-Oz said:


> I'm still waiting for their definition of throw to see if it is anything like my own personal definition which is simply the distance at which a particular torch can illiminate a dark target at a distance well enough to identify it wiht my set of eyes. I suspect that this forum's definition is going to be nothing even barely related to mine and that I am never ever going to see a measurement standard that will help me make that assessment when it comes to buying a new torch..........



My definition of throw is the same as yours. I need to be able to see the light with my unaided eyes. Throw isn't a laser a mile away that I can't see but it also has nothing to do with how big a beam is as long as I can see it.

If two lights can throw a hotspot 300 meters and no more and I can see them both but one has a large hotspot and one has a smaller hotspot they both have the same throw by my definition.

That's why lumen has little to do with throw except as it relates to brightness/emitter size.


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## JaguarDave-in-Oz (Mar 9, 2010)

gcbryan said:


> If two lights can throw a hotspot 300 meters and no more and I can see them both but one has a large hotspot and one has a smaller hotspot they both have the same throw by my definition.


Agreed.


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## JaguarDave-in-Oz (Mar 9, 2010)

So to come back to a more current and practical aspect could we please look at two torches. The first being the old version of the Eagletac P20C2 It has XR-E R2 led and throws quite well but I have to assume that it's not throwing to the absolute best that an R2 can throw (that bit will be important). Next we have the new version of the same torch which now has an XP-G R5 led and apparently does not throw as far.

My question is - is it possible for a reflector to be designed for version two or three of this new torch that will throw as far or further than the old previous XR-E version given what we know about surface brightness and the new aspect you've mentioned regarding the exit angle of the light? 

What I'm wanting is not a theoretical answer based on comparison with the best case scenario of what might have been possible with XR-E versus this new torch but more an answer that helps me in a practical way as a buyer of the newer R5 leds being that I want to know if the new ones can be made to throw as well or better than the older already existing not perfectly designed reflector systems in the old R2 versions.

I base the question on an idea that I have that the manufacturers are rushing to XP-G lights without putting time into perfecting the reflectors. I keep hearing excuses that they just won't throw as well as before simply because XP-G isn't as good at that as XR-E so leave it at that. My own experience with it was when I received two Quark Turbos, both with dark centres in the hotpsots. A fault that I was able to either eliminate or moderate simply by shimming the reflector out by varying amounts.


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## gcbryan (Mar 10, 2010)

I don't think it's likely that the new model with the XP-G is going to be able to throw as far as the older model with the XR-E.

I don't have those lights and you mention that you think that the XR-E model could be improved. I don't have any specific info regarding that.

I think as a practical matter you just have to decide what is more important to you...the best throw with a smaller hotspot or good throw with a larger hotspot.

After all as a practical matter it's rarely important to have the absolutely best throw unless it's just for bragging rights.

I'm sure with time you might find a reflector for the XP-G that results in better beam quality but it's not likely to be a big improvement in throw unless you just go to a much larger diameter head.

I'm no expert here but this is just my take on things. Regarding beam quality I'm finding I like TIR optics more and more for beam quality as opposed to reflectors or aspherics.


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## JaguarDave-in-Oz (Mar 10, 2010)

gcbryan said:


> After all as a practical matter it's rarely important to have the absolutely best throw unless it's just for bragging rights.


I don't have anyone to brag to out here but the further I can see with my torch the better off I am, there's actually no doubt about that, it's just the nature of what I do with my torch but it's also unfortunate that I have restrictions in that I must also compromise in having it fit comfortably in my pocket and be able to do some other more mundane tasks. I can't be the only person in that situation. I'm not actually here because I particularly enjoy flashlightaholism, I don't think I do. I just want to find the best torch for my particular use (and have tried about twenty so far) and then get on with it but it's taking a long time.



gcbryan said:


> I'm sure with time you might find a reflector for the XP-G that results in better beam quality but it's not likely to be a big improvement in throw unless you just go to a much larger diameter head.


and I guess that's what happened with the Quark Turbo over its smaller headed elder sibling the R2. The Turbo throws further (very noticeably under the ever more common out here dusty or humid conditions but that's another aspect of throw discussion for later I guess). 



gcbryan said:


> I don't have those lights and you mention that you think that the XR-E model could be improved. I don't have any specific info regarding that.


ok, perhaps for a more commonplace example, look at the Quark 123-2 XP-E R2. It's ok but my similarly driven XP-E Q5 Eagletac P100 craps all over it for throw so the improvement in throw must have come from reflector design.

What I'm trying to say is that most of the the R2 torches were not necessarily designed with anything like maximum throw in mind anyway so why would it not be beyond the realms of possibility to design a reflector for the bigger XP-G in the following versions of those models that will at least equal them in throw so that we get rid of this idea that when a particular brand "upgrades" its model xyz to XP-G R5 that one must accept that one will lose out on throw? I want to have my cake but I want to eat it too............


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## gcbryan (Mar 10, 2010)

JaguarDave-in-Oz said:


> I don't have anyone to brag to out here but the further I can see with my torch the better off I am, there's actually no doubt about that, it's just the nature of what I do with my torch but it's also unfortunate that I have restrictions in that I must also compromise in having it fit comfortably in my pocket and be able to do some other more mundane tasks. I can't be the only person in that situation. I'm not actually here because I particularly enjoy flashlightaholism, I don't think I do. I just want to find the best torch for my particular use (and have tried about twenty so far) and then get on with it but it's taking a long time.



I like to learn about these things more than I care about owning a bunch of flashlights. I came here only because of dive lights. I needed to learn a bit so that I could know how to either buy or build better dive lights.



> and I guess that's what happened with the Quark Turbo over its smaller headed elder sibling the R2. The Turbo throws further (very noticeably under the ever more common out here dusty or humid conditions but that's another aspect of throw discussion for later I guess).


Yes, a larger diameter reflector or optic captures more light and therefore throws further (my understanding anyway).



> ok, perhaps for a more commonplace example, look at the Quark 123-2 XP-E R2. It's ok but my similarly driven XP-E Q5 Eagletac P100 craps all over it for throw so the improvement in throw must have come from reflector design.
> 
> What I'm trying to say is that most of the the R2 torches were not necessarily designed with anything like maximum throw in mind anyway so why would it not be beyond the realms of possibility to design a reflector for the bigger XP-G in the following versions of those models that will at least equal them in throw so that we get rid of this idea that when a particular brand "upgrades" its model xyz to XP-G R5 that one must accept that one will lose out on throw? I want to have my cake but I want to eat it too............


I've seen pictures of the Quark and the Eagletec that you refer to but I can't tell everything about them. What looks different to you? Do they both use reflectors? Do they both have roughly the same diameter head?

You can of course have a XR-E that was designed for more flood and then replace it with A XP-G and reflector that was designed more for throw and out throw it but that doesn't really help you.

If you buy a XR-E that was well designed for the throw that you want and then the XP-G comes out and now you want to upgrade then the throw will be less. If you want throw then just don't get the newer XP-G. If throw is the most important why get the XP-G?

I understand that you want the bigger hotspot of a XP-G and the throw of a XR-E but that's not going to happen. You have to go for a compromise.

If you really just care about throw just go with a HID light or something like that. It sounds like you live in a place where that might be useful.


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## JaguarDave-in-Oz (Mar 10, 2010)

gcbryan said:


> You can of course have a XR-E that was designed for more flood and then replace it with A XP-G and reflector that was designed more for throw and out throw it but that doesn't really help you.


no, that's true, it won't help me until the the designers of the new models of the torches do it for me. And they should.



gcbryan said:


> If you buy a XR-E that was well designed for the throw that you want and then the XP-G comes out and now you want to upgrade then the throw will be less.


but that's my point - Why must this be so? Why not just refine the reflector some more at the same time as upgrading the led?



gcbryan said:


> If throw is the most important why get the XP-G?


In one particular torch's case there's 2 reasons, 1. It's brighter and more efficient and 2. the torch I'm looking at (P20C2) has had a significant improvement to what was previously a **** poor UI in the XP-E model that now means I can have one where before I would not entertain the previous one because of the crappy UI.



gcbryan said:


> I understand that you want the bigger hotspot of a XP-G


 actually no, I want a smaller hotspot (smaller seems to help cut through dust and humidity) and it's my understanding that the size of the hotspot in practice at say a hundred yards is merely a function of the reflector. That certainly seems to be the case when comparing my various brands of XP-E R2's, also when comparing my Quark R5 turbo (which after my reflector shimming has a nice small hotspot, proving adjustment to reflectors can do the job with XP-G) to my Quark R5 regular.



gcbryan said:


> If you really just care about throw just go with a HID light or something like that. It sounds like you live in a place where that might be useful.


I have all that stuff for when I really need it (after all I've been shooting ferals for money for thirty five years) but I want to take advantage of the pocket sized led revolution for my around the property life.

I also want my medium range pocket throwing torch to be able to do more mundane tasks as well as throw a distance and a modern high power pocket spot/spill torch should be just perfect for that arrangement, I'd just like twenty five yards further than the Quark Turbo. In fact I actually do have a torch that throws easily far enough and floods wide enough, my Led Lenser variable focus P7 but it lacks a few modes, a clip and is a bit "girthy" for the top pocket.............


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## JaguarDave-in-Oz (Mar 10, 2010)

Another thing I noticed and I'm not sure where it comes in between brightness and throw. Bare with me while I tell the story.

A fair while ago I gave my wife one of those five dollar eight led 3xAAA torches.

I was out mowing in a paddock about a hundred and fifty yards from our house yard fence. It's dark, I'm using the headlights on the mower (it's a big one). My wife wanted me to come in for a cup of tea so she came to that fence and started waving the multi led torch at me. Now that torch couldn't lightup the ground more than a few yards in front of her but it sure looked like a really bright ball of light waving around in her had from my position looking back at it.

So what's the go? It's not a throwy torch but the light is obviously travelling quite strongly a hundred and fifty yards out to where I was cos I could see it but she'd have been able to see nothing of me at that distance (other than the two big lights of my mower).


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## Th232 (Mar 10, 2010)

JaguarDave-in-Oz said:


> but that's my point - Why must this be so? Why not just refine the reflector some more at the same time as upgrading the led?



I *think* I get what you're saying, but I'm not entirely sure, so please tell me if I'm going in the wrong direction. For reflectors, the fundamental shape behind most of them is a parabola, the shape required to take light from an infinitely small point and project it with all rays parallel to its axis. Mathematically, that's the most efficient shape, so for a given size, improving on it in that respect is impossible as far as I know it, short of rewriting the laws of physics.

That said, LEDs aren't a point source, and so there's the question of juggling how all the die images get reflected and in which directions they go. This has been worked out quite well, so there really isn't much space, at least not that I can see.

The most innovative reflector I know of is more of a hybrid, made by Polymer Optics. Here's the datasheet for the XR-E version. It takes the part of the LED output that you fundamentally can't focus for a given size reflector (the spill), and instead captures it with a lens and projects that forward. Disadvantages, it's now more than one pieces (it's 8 now), and from my experience the lens detaches quite easily, so you have to glue it in place (fortunately an easy task). I'd love to see more that type though.

Regarding the story of your wife using the multi-led torch, you can see your wife because:

* Light travels straight towards your eyes. Some is reflected off the ground then on to you, but that's minimal. Grass, humans and so on aren't exactly very reflective.

Your wife can't see you because light has to:

* Travel to you, noting that a lot of that light will miss you altogether. This is the same as above, but then it also has to:
* Reflect off you, and as said, grass, dirt, humans &c. aren't very reflective.
* Reflect off you in the correct direction and not get bounced back to the left, right, above or below of her, or even a couple of cm away from her eyes.

I think it's that, but I could very well be wrong.


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## gcbryan (Mar 10, 2010)

JaguarDave-in-Oz said:


> ...
> 
> but that's my point - Why must this be so? Why not just refine the reflector some more at the same time as upgrading the led?



You can't refine the reflector to the point of creating greater brightness that the led can emit in the first place. The XR-E is brighter than the XP-G. If you take away both reflectors and just stare at the bare led the XR-E is brighter.

A reflector can't make it any brighter than it is. If you have a lousy reflector you can of course make a better one but if the XR-E had a good reflector then you can't make the reflector for a XP-G so much better to make up for the greater brightness of the XR-E.

Throw starts with led surface brightness which is determined only by the led itself.


> In one particular torch's case there's 2 reasons, 1. It's brighter and more efficient and 2. the torch I'm looking at (P20C2) has had a significant improvement to what was previously a **** poor UI in the XP-E model that now means I can have one where before I would not entertain the previous one because of the crappy UI.



The torch may be brighter if it's being driven harder than the older torch but if everything else is the same the XP-G isn't brighter, it's just got more lumens...bigger hotspot...more spill, etc.

The UI is not really a technical problem it's just a marketing problem which drives us all nuts when there is a product that could be made a lot better but no one is doing it.

That's why I look at building my own dive lights...because I don't like they way others are doing it.



> actually no, I want a smaller hotspot (smaller seems to help cut through dust and humidity) and it's my understanding that the size of the hotspot in practice at say a hundred yards is merely a function of the reflector. That certainly seems to be the case when comparing my various brands of XP-E R2's, also when comparing my Quark R5 turbo (which after my reflector shimming has a nice small hotspot, proving adjustment to reflectors can do the job with XP-G) to my Quark R5 regular.



The hotspot is determined by the size of the led and the reflector. When you keep everything else the same and just switch the led from XR-E to XP-G you will be a larger hotspot because there is more light with the XP-G that hits the reflector (light that hits the reflector goes to the hotspot and the light that doesn't hit the reflector is the spill). It's not quite as bright but it's larger. If it was just as bright then the larger hotspot would throw just as far as the smaller hotspot.



> I have all that stuff for when I really need it (after all I've been shooting ferals for money for thirty five years) but I want to take advantage of the pocket sized led revolution for my around the property life.
> 
> I also want my medium range pocket throwing torch to be able to do more mundane tasks as well as throw a distance and a modern high power pocket spot/spill torch should be just perfect for that arrangement, I'd just like twenty five yards further than the Quark Turbo. In fact I actually do have a torch that throws easily far enough and floods wide enough, my Led Lenser variable focus P7 but it lacks a few modes, a clip and is a bit "girthy" for the top pocket.............



I don't know if the P7 has any modes but there are cheap lights on DX (I have one) that do more or less the same thing as the P7 as it understand it. I'm talking about the so called "flood to throw" lights using an aspheric lens. Mine throws pretty well and the flood is good and it has 2 modes (high and low) as well as the usual (for DX lights) strobe.

There's nothing fancy about it (it's a $15 light) but it uses the XR-E and an aspheric. It probably isn't driven quite as hard as your P7 so yours may throw even further.

I understand your frustration...it's hard to find the perfect light. The people on here who are really into lights have many lights (not me) for just that reason in my opinion...no one ever finds the perfect light.

There really aren't many adjustable focus lights (like the P7) that have a great UI and that have more output. They usually have in the 100-220 lumens range.

I think in general it's just easier to find a light that you feel is the best for throw and another one for all around use and as long as they are small just carry both


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## gcbryan (Mar 10, 2010)

JaguarDave-in-Oz said:


> Another thing I noticed and I'm not sure where it comes in between brightness and throw. Bare with me while I tell the story.
> 
> A fair while ago I gave my wife one of those five dollar eight led 3xAAA torches.
> 
> ...



It tells us that we can see a light equally when it's either big and not so bright or bright and not so big. It's kind of like the concept of a laser I suppose. It doesn't illuminate much but you can see it from a long way off.

The light isn't throwing the way we usually use the term in flashlights because by throw we mean illuminate something while we are holding the light. 

When all you have to do is spot the source of a light you can do that from a much greater distance. At night in the city (I'm on a hill) I can see a window in a house probably a mile away that can't be lit by anything more than a 100 W bulb. That same bulb screwed into my back porch socket would only illuminate my porch.


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## gcbryan (Mar 10, 2010)

Th232 said:


> I *think* I get what you're saying, but I'm not entirely sure, so please tell me if I'm going in the wrong direction. For reflectors, the fundamental shape behind most of them is a parabola, the shape required to take light from an infinitely small point and project it with all rays parallel to its axis. Mathematically, that's the most efficient shape, so for a given size, improving on it in that respect is impossible as far as I know it, short of rewriting the laws of physics.
> 
> That said, LEDs aren't a point source, and so there's the question of juggling how all the die images get reflected and in which directions they go. This has been worked out quite well, so there really isn't much space, at least not that I can see.
> 
> ...



I think the general type of "reflector" you are talking about (correct me if I'm wrong) is TIR (total internal reflection). I'd refer to it as an optic...it's just not an aspheric.

Maybe you are talking about something else though.

I have a few cheaper TIR type of optics and I've replace several reflectors with them and I like the result. It does have a little collimating lens that would capture that part of the emitter light that would have gone straight out missing the reflector.

The rest of the light is reflected within the lens or optic (I'm not clear on all the details). The result for me is that it makes the hotspot a little brighter and in my case a little smoother and it takes away some of the brightness of the spill and takes away most of the hard outer edge of the spill.

I use it in one of my dive lights where a brighter hotspot cuts through the limited viz water better and the spill in some cases would just create backscatter so less is better.

The optic I use is just a direct snap-on replacement for a reflector and it snaps on to a XR-E die.

It this more or less the same type of design you are talking about?


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## JaguarDave-in-Oz (Mar 10, 2010)

Th232 said:


> I *think* I get what you're saying, but I'm not entirely sure, so please tell me if I'm going in the wrong direction. For reflectors, the fundamental shape behind most of them is a parabola, the shape required to take light from an infinitely small point and project it with all rays parallel to its axis. Mathematically, that's the most efficient shape, so for a given size, improving on it in that respect is impossible as far as I know it, short of rewriting the laws of physics.


alright yes, you're getting me and I'm getting what you're saying and I'm assuming that in a perfect world the parabola might be the optimum shape for the reflector.

The next question then is that while they are all apparently "based" on parabolas, are they actually true parabolas or just Fred Nerk the torch designer's personal modified version of a parabola adapted to the non perfect ligth source, being that some reflectors project what I call "tightly focussed beams" and others of apparently similar size project very dispersed beams? If that's true then maybe some may be further from parabolas than others and thus have room for "tuning" or another personal adaptation from the designer? What's the tighttest possible beam able to be attained via a reflector from say an XP-E? is there a way of calxculating that given the non perfect point source arrangement or is it always just trial and error? Do any reflector torches on the market actually have beams with absolutely optimum focus?

I'm still trying to undertsand the actual mechanics of how one might change a reflector design to influence the angle of the centre beam so maybe I need to look at it in reverse, what if I wasn't looking for the designers to make the new beams more focussed, what if I wanted them to spread them out more. How might they change the reflector to do that?

I had read so many times with reviews of so many different torches that one reviewer or another believed it would have extra floodiness or extra throw based on his perception of whether the particular torch's reflector was really deep or really shallow. Was that theory wrong and also inapplicable to the XP-G?


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## JaguarDave-in-Oz (Mar 10, 2010)

gcbryan said:


> I don't know if the P7 has any modes but there are cheap lights on DX (I have one) that do more or less the same thing as the P7 as it understand it. I'm talking about the so called "flood to throw" lights using an aspheric lens. Mine throws pretty well and the flood is good and it has 2 modes (high and low) as well as the usual (for DX lights) strobe.
> 
> There's nothing fancy about it (it's a $15 light) but it uses the XR-E and an aspheric. It probably isn't driven quite as hard as your P7 so yours may throw even further.


I have the upgraded Romisen rc-c6 II Q5 from Shiningbeam and it's what got me started on this business of wanting to see focussing of the led done better. Even small changes to the focus on that torch make a noticeable difference to how far I can see with it. Both it and the LLP7 have shown me that even with lowly lumen output a well focussed beam can help me see a lot further than a brighter less focussed one.



gcbryan said:


> I understand your frustration...it's hard to find the perfect light.


but crikey I'm so darned close..... The quark 2-123 turbo has almost everything I need (now that I've fixed its hotspot), it's got momentary on high and low, protruding switch, head twist mode switching between high and low, hidden strobe, decent throw, grippy knurling and pocketability. Alls I really need to have it perfect is twenty five yards extra throw (to reach from fence to fence in my little paddocks) and about a quarter inch less head diameter. In theory that describes the P20C2 XP-E R2 but with the mkII UI so I have to take a punt on the throw of the XP-G. If the P20C2 doesn't work out then I won't kill myself cos the QTurbo will do for now, it's just that I want that cake.....


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## Th232 (Mar 10, 2010)

gcbryan said:


> I think the general type of "reflector" you are talking about (correct me if I'm wrong) is TIR (total internal reflection). I'd refer to it as an optic...it's just not an aspheric.
> 
> Maybe you are talking about something else though.
> 
> ...



Nope, this one's a true hybrid, no TIR component. There's an opaque metallised plastic component, which is the reflector component and will reflect light no matter the angle of incidence (well, for all practical purposes), then a fresnel lens over it, which captures any side spill. Here's a picture of one I have (looks different from the datasheet because I trimmed down), fully assembled, and with the fresnel lens removed (observe that you can't see the table at all through it, as you would with a TIR):









JaguarDave-in-Oz said:


> alright yes, you're getting me and I'm getting what you're saying and I'm assuming that in a perfect world the parabola might be the optimum shape for the reflector.
> 
> The next question then is that while they are all apparently "based" on parabolas, are they actually true parabolas or just Fred Nerk the torch designer's personal modified version of a parabola adapted to the non perfect ligth source, being that some reflectors project what I call "tightly focussed beams" and others of apparently similar size project very dispersed beams? If that's true then maybe some may be further from parabolas than others and thus have room for "tuning" or another personal adaptation from the designer? What's the tighttest possible beam able to be attained via a reflector from say an XP-E? is there a way of calxculating that given the non perfect point source arrangement or is it always just trial and error? Do any reflector torches on the market actually have beams with absolutely optimum focus?
> 
> ...



*Short version*
For better throw you want:
As perfect a parabola as you can get
A larger reflector to reduce the error arising from a finite die size.
A deeper reflector, but I guess there's a limit to that.

*Long version*
I would expect that no reflectors are perfect parabolas because of surface finish. Apologies if I'm repeating something you already know, but to increase beam quality, an orange peel finish is often used, but by smoothing out the beam, you reduce throw, hence why smooth reflectors throw better than their OP equivalents. As such, even though the original shape may be a parabola, it most definitely isn't once you take the finish into account. Likewise, even for smooth reflectors, the surface isn't going to be perfect, so there will be issues. In that case, the question is how much do you want to pay for such a reflector? We're building a polishing system at work that should get us a 3.25 nanometre surface roughness, but the cost will naturally be quite expensive.

On the design aspect of things:

To throw better, if you take a reflector and scale it up, it will throw better because the LED die will more closely approximate a point source, thus leading to better collimation. For a given diameter, a deeper reflector will collect more light, which will also help. While a narrower reflector sounds like it might be better, bear in mind that courtesy of the finite die size there will be a point where you're catching light that's already been reflected, and sending it off in a direction that's decidedly not parallel to the reflector's axis. Simply put, you're stuck with a hole at the end which will let out a certain amount of light whether you like it or not.

I just remembered this and should correct my earlier statement, there are also some conical reflectors out there, but those are more for creating an even flood than any kind of throw. I suspect that to create a floodier beam, you change the reflector cross-section from a parabola to a cone, but I'm not entirely sure about that.


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## JaguarDave-in-Oz (Mar 10, 2010)

Thanks, my brain is accomodating that information better than I expected (especially the bit about the larger reflector making the led seem a bit more like a point than the same size led in a small reflector). 

And no, you're not really telling me anything I already knew as I'm pretty much flying blind here (and certainly out of my depth).

Which leads me to something else that was mentioned earlier. It was said that one or other of the LED versions lets out light over an angle of 120 degrees and the other at ninety. My experiment some time back with my TK20 showed me that I could blank out the spill by putting a silver dot in the middle of my lens so therefore I assume that the middle angle of the led is where the spill comes from, perhaps because that's the part that does not get reflected by the reflector and thus does not get focusssed.

If that's the case does the led that lets light out at 120 degrees get more light in the spot due to more light hitting the reflector and thus beinfg focussed or is that an oversimplification?


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## Th232 (Mar 10, 2010)

You're pretty close there. I'd say the 120 deg LED would be one with a Lambertian distribution (SSC P4, Lux 3 or any other number), while the 90 deg would be an XR-E.

The way I view it, there're three parts to a beam coming from an LED/reflector combination.

First, the beam parallel to the axis, or nearly so. This is from 0 degrees to however wide the hotspot is. This light goes straight, and contributes to the hotspot.

As you move further, you've got an area where the light isn't being reflected, but is outside of the hotspot, creating the spill.

Note that your silver spot would have been reflecting both of the above, I'm not sure how much a difference the first part makes, did you notice any change in brightness of the hotspot when you had the spot?

Third part, the light that gets reflected. As you can guess, this would ideally go straight forward, but doesn't. This also contributes to the hotspot. I haven't actually thought about the ratios, so I can't really say anything as to how much either contributes to the hotspot relative to the other.

Note that the hotspot and the spill expand at different rates, so in the case of my Quark, the contribution of part 1 to the hotspot will decrease the further you go out, or at least it looks like that from my close-range tests. I think this is universal, but I'm not entirely sure?

As such, I believe an ideal LED would have all its light in parts 1 and 3, but with the above statement, part 3 would be ideal, assuming the reflector would perfectly reflect the image of the die from any angle. That said, it won't perfectly reflect the image of the die, and unfortunately it's about 2330 at the moment and my brain's kinda shut down, so I'm not sure about how it goes from there. Hopefully someone else can chime in while I'm off to sleep.


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## JaguarDave-in-Oz (Mar 10, 2010)

Th232 said:


> Note that your silver spot would have been reflecting both of the above, I'm not sure how much a difference the first part makes, did you notice any change in brightness of the hotspot when you had the spot?


Yes indeed, I found that the hotspot's intensity was noticeably diminished which is why it actually ended up merely being an experiment rather than a permanent mod..............


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## bshanahan14rulz (Mar 10, 2010)

Reflectors are like TIRs, except the extra light is spilled instead of redirected into the hotspot.

For a reflector beam pattern, imagine a circle the size of the reflector opening cut in paper. Put that paper with a hole over a naked LED right where the outer rim of the reflector would be, and you have the "spill" component of the beam. An even circle of light.
The reflector takes the light that was blocked by the paper with a hole in it, and redirects it forward into the hotspot.


larger source increases divergence if using the same optic
larger optics are able to decrease divergence more than smaller ones if using the same source

Many reflectors and optics are designed for a point source. I believe (this is just speculation, btw) that some TIRs are engineered with a square source in mind. I say this because I have a LisaXP optic for a cree xp-e, and there are artifacts in the central column that shouldn't be there if they are trying to create a perfect beam from a point source. almost looks like a 4-leaf clover.

But yeah, very nice discussion, you two! Where's that stupid I <3 cpf smiley....


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## gcbryan (Mar 10, 2010)

I have a reflector question as it relates to throw and yes I do understand that the part of the emitter beam not reflected is the spill.

The question is in regards to reflector depth. Reflector width (diameter) collects more of the emitter light beam with increasing diameter and that contributes to throw.

Does reflector depth also contribute to throw or simply to something else such as less spill or something. I'm not entirely clear on this aspect of reflectors. I would think it would collect more of the forward directed beam that if not collected would result in spill. I would think this would result in greater throw as well. Somewhere I seem to remember reading that this is not the case but that doesn't sound right to me.


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## uk_caver (Mar 10, 2010)

gcbryan said:


> The question is in regards to reflector depth. Reflector width (diameter) collects more of the emitter light beam with increasing diameter and that contributes to throw.
> 
> Does reflector depth also contribute to throw or simply to something else such as less spill or something. I'm not entirely clear on this aspect of reflectors. I would think it would collect more of the forward directed beam that if not collected would result in spill. I would think this would result in greater throw as well. Somewhere I seem to remember reading that this is not the case but that doesn't sound right to me.


I'm not sure I'd say that increasing width captures more light.
For a given shape (ie given focal length) of parabola, increased _size_ captures more light, but that's by the front rim going forwards as well as sideways as the reflector gets larger.

A deep/narrow reflector will have good 'capture', but might not have amazing throw if the beam doesn't end up being very tight.

The way I think about it is imagining being at a point on a reflector, looking back towards the LED, with the LED being thought of as a flat emitting surface of a certain width.
With a deep+narrow reflector, from a point 'P' some way out on the reflector, looking back towards the LED, it's being looked at from _relatively_ square-on, and from a short-ish distance, so light coming from one side of the LED is arriving at a somewhat different angle than light coming from the other side of the LED.
Because the light from the LED is coming in at reasonably different angles, light bouncing off the reflector is leaving at a range of angles, and the beam has a fair spread to it.

Imagine a parabolic reflector of the same depth, but wider. At a point on that reflector at the same distance forwards as point P on the narrow reflector, looking towards the LED, the LED is further away, and appears more edge-on - the difference in angle between incoming light coming from one side of the LED and from the other side of the LED isn't as great, so the light reflected off the reflector at that point has a smaller spread of angles to it. The beam diverges less, and so doesn't spread out and lose intensity as fast with distance.
Even imagining going closer to the LED along the reflector, shortening the distance, the LED then seems even more edge-on, so the variation in angle of incoming light is still small.

Though for a given depth of reflector, less light will hit a wider reflector, the wider reflector could give a beam that's more nearly parallel.


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## gcbryan (Mar 10, 2010)

Th232 said:


> ...
> 
> To throw better, if you take a reflector and scale it up, it will throw better because the LED die will more closely approximate a point source, thus leading to better collimation. For a given diameter, a deeper reflector will collect more light, which will also help. While a narrower reflector sounds like it might be better, bear in mind that courtesy of the finite die size there will be a point where you're catching light that's already been reflected, and sending it off in a direction that's decidedly not parallel to the reflector's axis. Simply put, you're stuck with a hole at the end which will let out a certain amount of light whether you like it or not.



That's the kind of explanation I was looking for! Particularly the comments about scaling up makes the emit for like a point source.

Thanks.


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## gcbryan (Mar 10, 2010)

JaguarDave-in-Oz said:


> but crikey I'm so darned close..... The quark 2-123 turbo has almost everything I need (now that I've fixed its hotspot), it's got momentary on high and low, protruding switch, head twist mode switching between high and low, hidden strobe, decent throw, grippy knurling and pocketability. Alls I really need to have it perfect is twenty five yards extra throw (to reach from fence to fence in my little paddocks) and about a quarter inch less head diameter. In theory that describes the P20C2 XP-E R2 but with the mkII UI so I have to take a punt on the throw of the XP-G. If the P20C2 doesn't work out then I won't kill myself cos the QTurbo will do for now, it's just that I want that cake.....



Well, except for the size of the head you could make the Quark even closer to your perfect light by simply switching the XP-G R5 emitter with the XR-E R2 emitter and you'll get extra throw. If the reflector is OP changing that to a smooth reflector will improve throw as well.

It sounds like you could get the throw you want in your almost perfect light. The head would still be the same size however but that contributes to throw as well.


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