LED Surface Brightness Question

[gcbryan]

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.

 

[gcbryan]

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.

 

[Paul Baldwin]

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 http://www.candlepowerforums.com/vb/showthread.php?t=261915&page=3 Saabluster is the resident guru in these matters

 

[bshanahan14rulz]

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.

 

[gcbryan]

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.

 

[Linger]

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.

 

[JaguarDave-in-Oz]

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?

 

[gcbryan]

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.

 

[gcbryan]

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.

 

[JaguarDave-in-Oz]

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..........

 

[JaguarDave-in-Oz]

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).

 

[gcbryan]

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.

 

[gcbryan]

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.

 

[JaguarDave-in-Oz]

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.

 

[JaguarDave-in-Oz]

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.

 

[gcbryan]

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.

 

[JaguarDave-in-Oz]

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.

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).

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............

 

[gcbryan]

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.

 

[JaguarDave-in-Oz]

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.

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?

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.

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.

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.............

 

[JaguarDave-in-Oz]

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).