# Reflector Decision for Aspherical Lens



## sonikaccord (Dec 23, 2013)

Hello everyone, I am building a torch from scratch using a Vero 29. I need help deciding which type of reflector yields the best possible performance:

Parabolic + Ashperical
Elliptical + Ashperical
Or only reflectors.

My goal is to have a beam with very little divergence from the light while capturing as much of the spill as possible.


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## Norm (Dec 23, 2013)

:welcome:

An aspherical lens usually has no reflector or one that has been painted black

Norm


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## sonikaccord (Dec 23, 2013)

Thanks!

I reviewed the datasheet again and most of my output is emitted within 120 degrees. Am I correct in assuming that the black reflector is for absorbing the spill? If that's the case, designing the optics would be tons easier.


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## Norm (Dec 23, 2013)

You can try it with a reflector but from my experience you will see a lot of unwanted rings around the main beam.

Norm


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## DIWdiver (Dec 23, 2013)

Yes, the black reflector is to absorb spill. 

Any light that comes directly from the LED and gets into the lens, goes into the hotspot. Any light that bounces around inside the light and then gets into the lens, becomes spill. So to minimize spill, everything in the chamber between the LED and the lens should be not only black, but flat black. This will not increase the hotspot, but only decrease the spill.


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## Dark Laser (Dec 24, 2013)

Why are systems with a condenser / pre-collimator lens not more popular? Spill light is catched and sent into the spot instead of wasting it. I understand that the setup is not the easiest, though.
By the way, has anyone lux numbers for a Maglite-size aspheric lens combined with a XP-G? With the deep reflectors and de-domed LED the lux numbers are quite impressive; so I wonder if an aspheric can beat that.


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## HarryN (Dec 24, 2013)

Dark Laser said:


> Why are systems with a condenser / pre-collimator lens not more popular? Spill light is catched and sent into the spot instead of wasting it. I understand that the setup is not the easiest, though.
> By the way, has anyone lux numbers for a Maglite-size aspheric lens combined with a XP-G? With the deep reflectors and de-domed LED the lux numbers are quite impressive; so I wonder if an aspheric can beat that.



There have been a few lights built with 2 stage optics, but not really that many people are equipped to do it. The precision and custom alignment needed is beyond the tools that most people have.

I built a light with a 12 mm diameter 2 stage setup (reflector plus Fresnel lens) and it was a significant learning experience, and quite costly in test / prototype parts. Optical physics is not a strength of mine and it would have been much cheaper of course if I had the guidance of an expert in this area. For 50mm size designs, it is of course much easier, but still requires both optics knowledge and the tools, or enormous patience.

Lastly, 2 stage optics make the most sense when the apparent light source is very small and high intensity (which was my big downfall at the time). It is much easier to purchase larger area LEDs and build them up with somewhat larger single stage optics, but of course not quite as impressive.

The other path people tend to take is to just use an HID source instead of the LED for these kinds of applications, because those are easier to build up for "super throwers".


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## sonikaccord (Dec 24, 2013)

HarryN said:


> There have been a few lights built with 2 stage optics, but not really that many people are equipped to do it. The precision and custom alignment needed is beyond the tools that most people have.
> 
> I built a light with a 12 mm diameter 2 stage setup (reflector plus Fresnel lens) and it was a significant learning experience, and quite costly in test / prototype parts. Optical physics is not a strength of mine and it would have been much cheaper of course if I had the guidance of an expert in this area. For 50mm size designs, it is of course much easier, but still requires both optics knowledge and the tools, or enormous patience.
> 
> ...


 
I have decent knowledge in optics. I understand the concepts and such. When you say "apparent light source," that means the size of the source before it hits the final lens? I've researched pre-collimators but it would have to be adjustable focus on both lenses as a prototype to get the best output.

Since we're on the topic, the LES (light emitting surface) has a diameter of 29.2mm with no optics. I'll see if I can pull up some equations and such to tighten the beam up in a theoretical sense.


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## alpg88 (Dec 24, 2013)

waiven light colar.


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## sonikaccord (Dec 24, 2013)

I checked out the Waiven light recycling tech. It sounds like a good idea esp since there is so much phosphor in the led that can be excited by that technique. I'll have to try it out once I get the led and build the heatsink.


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## DIWdiver (Dec 24, 2013)

A source with a 29mm diameter is only good for flood lighting. Any optic, either lens or reflector, large enough to create any kind of tight beam would be huge. If you want a flood, then you want a shallow reflector just to push the widest of the spill toward the front. If you want any kind of beam, pick another emitter.


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## sonikaccord (Dec 24, 2013)

Thanks for that advice. I will still get the emitter to experiment with, but I won't have my hopes up for a tight clean beam. I've looked up emitter sizes and they should be as close to a point source as possible for max throw.

However, could I use a converging lens to shrink the "apparant source?" Then have the aspheric take over? I realized that matching the focal points would result in a large system, just wondering if it's possible.


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## inetdog (Dec 24, 2013)

No it is not. You cannot get rays in all directions from all parts of the emitter to converge in one place. If the emitter beamed the light strongly in one direction you could do better, but not with an omnidirectional emitter surface.

Sent from my XT1080 using Tapatalk


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## sonikaccord (Dec 24, 2013)

Awesome, I have more research to do. You guys have been great.


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## HarryN (Dec 25, 2013)

Sonikaccord - I spent a great deal of money and time on exactly trying to accomplish exactly what your question asks. Of course others told me that it would not work, and I still tried anyway. Yes, I read the physics books that explain it, but I still could not bring myself to intuitively accept the answer.

What I can say about it, is that while I still don't intuitively understand "why" it is true, my experiments (and wallet) made me a believer that the key to "throw" is a high surface brightness, compact light source. I just could not get a similar "total lumens", but larger light source to achieve high lux levels, even with multi stage optics.

OMG is a custom flashlight company that makes some flashlights with amazing throw. While not cheap, buying one of those is still likely cheaper than attempting to build your own, of course, not quite as satisfying though.


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## sonikaccord (Dec 26, 2013)

I have seen the OMG DEFT-X and it is a beautiful work of art. That's also where I saw the Waiven RLT used. I think this will end up turning more into a learning experience than anything. I have built my own LED flashlight from off the shelf parts, but I think it will be very educational to build my own from scratch, play with a couple of lens designs and see the theory in action. 

I have been searching through other people's threads seeing what mistakes they made, what worked, what they would've done differently, etc. Experiences like HarryN's really help because they have done it already.


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## TEEJ (Dec 26, 2013)

The only ways I'd see an increase from standard uses:


if the LED was aimed BACK at the reflector, and the reflector focused a point source where the aspherical lens could then project it from the flashlight. IE: Use the reflector to simulate a smaller point source than otherwise possible.

if the LED was projected as a SMALLER image onto a second aspherical lens that then used THAT image as a smaller point source, and so forth.


As mentioned though, that's a lot of precision aiming going on.


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## DIWdiver (Dec 26, 2013)

From what I've read, the consensus is that you cannot create a smaller image of the original source with increased intensity. It's not just impractical, it's theoretically impossible.


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## TEEJ (Dec 26, 2013)

DIWdiver said:


> From what I've read, the consensus is that you cannot create a smaller image of the original source with increased intensity. It's not just impractical, it's theoretically impossible.



Tell that to the ants I popped with a magnifying glass.




What if I simply mounted the LED at an angle, so instead of a flat block, it was at a 45º angle. The intensity would be the same, but the apparent size would be cut in half. It would also tend to send more photons at the reflector wall and fewer out the front as spill.


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## sonikaccord (Dec 26, 2013)

That's what I was saying earlier. Minify the apparent size of the source so that the focal point of the first lens is at the focal point of the second lens.

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## Esko (Dec 27, 2013)

TEEJ said:


> What if I simply mounted the LED at an angle, so instead of a flat block, it was at a 45º angle. The intensity would be the same, but the apparent size would be cut in half. It would also tend to send more photons at the reflector wall and fewer out the front as spill.



First of all, it wouldn't be cut in half but in ~70% (if dedomed - something like 80% if not). The output is degreased to some ~70%, too. You can check (for example) the XM-L data sheet for typical spatial distribution here:

http://www.cree.com/~/media/Files/C...d Modules/XLamp/Data and Binning/XLampXML.pdf

Perhaps you should have suggested that the led should be mounted at a 90º angle (or 89,999º angle)? It would make the "apparent size" infinitely small, right? (Used in Spark SP6, btw). This aproach doesn't make the light infinitely throwy, though. It just means that the light is emitted to another direction (to the side).



TEEJ said:


> Tell that to the ants I popped with a magnifying glass.



According to this source, the total radiation power of Sun surface is 62,9MW/m^2 or 6,3kW/cm^2. I think that this (or the amount of visible light which is roughly 50% of it) should be the base for your comparison.


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## TEEJ (Dec 27, 2013)

Esko said:


> First of all, it wouldn't be cut in half but in ~70% (if dedomed - something like 80% if not). The output is degreased to some ~70%, too. You can check (for example) the XM-L data sheet for typical spatial distribution here:
> 
> http://www.cree.com/~/media/Files/C...d Modules/XLamp/Data and Binning/XLampXML.pdf
> 
> ...



Thanks for the corrections - and yes, I hate when the phone auto corrects and truncates things...but, it happens. 

So as a wavien collar is simply reflecting light back at the led...The concept of an off angle led bounced to where the photons need to go...maybe a tented led etc...could be used to have more lumens in a smaller footprint. 

I think the limiting factor, as you alluded to, is that the lenses can only compress the image, but not the lux.

That leaves the image with the same or less lux, albeit in a smaller area. 

So a side or rear throw led setup might have some promise. ..but the reflector for it would be interesting


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## DIWdiver (Dec 27, 2013)

I think you'll find once you do the math, that you still can't make an image with higher intensity. It's been discussed at great length by experts, and they ended up agreeing it's impossible. Using reflectors doesn't get you around the laws of physics.


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## Esko (Dec 27, 2013)

Of course, one could plate most of the led primary optics with reflective surface, leaving only small part transparent. Perhaps the optics could be modified, too (a truncated cone for example). Some light would go straight through (like in a stock led), some would be reflected back to the phosphors (wavien collar effect) and some would be reflected from the plated surface and escape through the transparent top. Of course, plenty of light would be lost in internal reflections but the tiny spot would be brighter. What is the optimal shape of the optics and the optimal size of the transparent part and would it be brighter than a smaller sized stock led with high surface brightness? Those are the key questions and I don't have any answers to them.


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## inetdog (Dec 27, 2013)

TEEJ said:


> Tell that to the ants I popped with a magnifying glass.
> 
> 
> 
> ...



As far as the ants are concerned, the critical difference is that the sun is for all practical purposes at infinity. All of the rays hitting the reflector from one part of the sun are effectively parallel. 
When the large LED emitter surface is close to the lens you cannot focus all of the light from one part of the surface to the same point where the light from the other parts of the surface will be focused.
That is the problem you cannot avoid or work around.

Sent from my XT1080 using Tapatalk


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## TEEJ (Dec 27, 2013)

inetdog said:


> As far as the ants are concerned, the critical difference is that the sun is for all practical purposes at infinity. All of the rays hitting the reflector from one part of the sun are effectively parallel.
> When the large LED emitter surface is close to the lens you cannot focus all of the light from one part of the surface to the same point where the light from the other parts of the surface will be focused.
> That is the problem you cannot avoid or work around.
> 
> Sent from my XT1080 using Tapatalk



I agree.

I'm throwing stuff against the wall to see if anything sticks. Sometimes that illuminates a direction to go.

Right now, the throw is mostly limited by a lack of collimation, for the same reasons. As most of the lumens thrown forward by the LED that miss the reflector, ironically, are the ones LEAST likely to end up in the hotspot, I'm just playing with ideas that might get them back in line.

If the LED is angled back at the bowl at a 45º angle for example instead of on a flat block, and the bowl has a wavien collar-like bulge to redeirect the light to intensify the output, and then aim it OTF, it might work to better salvage the missing lumens.

If more LED are added, in a tent-like arrangement, they could fit more compactly, and distribute the light more evenly to start with, with none aimed straight out of the bowl w/o being collimated. 


IE: If four LED are focused onto one point, and that point is then the effective emission source, it could be brighter than 1 LED even if the same size.


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## sonikaccord (Dec 27, 2013)

^^^This. You can only focus some of the light. The rest goes to some place where you don't want it to. My goal was to collect as much as possible and redirect it to the aspheric, hence the idea for the reflector to gather the light. I got the idea from hid car headlamps but I don't think it can translate to a focused beam.

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## HarryN (Dec 30, 2013)

I don't claim at all to be an optics expert, but the way I understand it, the reason that using the sun and a magnifying glass works is that the sun is actually quite a high surface brightness source. Yes it also helps a lot that the rays reaching the earth are essentially parallel, but I think the surface brightness effect dominates the question. This might be only partially correct though.

In the particular case I was working on, (some time ago), I used a Philips Lux III (1 die, around 100 lumens at that time I think) vs a Lux V (4 die at around 200 lumens). The surface brightness of the Lux III was higher, and the total lumens from the Lux V was higher. My idea was conceptually similar, use 2 stage optics to capture and direct the light into a high Lux beam.

The approach also followed concepts from existing lights, such as car headlights (which routinely include a reflector and lens), as well as stage lights. I won't say that it cannot be done, but I was never able to make the lower surface brightness LED (even with more lumens) have the lux / throw of the higher surface brightness part, although I did achieve reasonable results. 

I have been told that this is an intrinsic optical property, and my wallet agrees with that concept, but that does not mean I really understand it. Someday I hope to though.


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## HarryN (Dec 30, 2013)

HIDs are quite high surface brightness sources, which is what makes them so interesting. If package size is not really an issue for you, you can start with some pretty reasonably priced auto HID lights and accomplish amazing things.


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## dc38 (Dec 30, 2013)

HarryN said:


> HIDs are quite high surface brightness sources, which is what makes them so interesting. If package size is not really an issue for you, you can start with some pretty reasonably priced auto HID lights and accomplish amazing things.



I think it's also important to take into account the light source's distribution angles. With a reflector, the light is captured and thrown forward out the front at many different angles. With an aspheric, only the light that hits the lens will get thrown forward. With a TIR, there is still loss of light, but is an attempt at combining a reflector shape with optic throw. If you want more light OTF, you can try chroming the slopes of the TIR to act as an actual reflector. It really does increase OTF light.

*/
=)
*\
pretend that's a right facing TIR and the = is the LED. Chrome the slopes where the asterisks * are.


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## TEEJ (Dec 30, 2013)

dc38 said:


> I think it's also important to take into account the light source's distribution angles. With a reflector, the light is captured and thrown forward out the front at many different angles. With an aspheric, only the light that hits the lens will get thrown forward. With a TIR, there is still loss of light, but is an attempt at combining a reflector shape with optic throw. If you want more light OTF, you can try chroming the slopes of the TIR to act as an actual reflector. It really does increase OTF light.
> 
> */
> =)
> ...



This DOES look like my idea of reflectors angled back at the LED/Bowl to salvage more light, etc.


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## sonikaccord (Dec 30, 2013)

HarryN said:


> I don't claim at all to be an optics expert, but the way I understand it, the reason that using the sun and a magnifying glass works is that the sun is actually quite a high surface brightness source. Yes it also helps a lot that the rays reaching the earth are essentially parallel, but I think the surface brightness effect dominates the question. This might be only partially correct though.



I've been looking at solar collectors during my search where they attempt to take advantage of the sun's surface brightness by "condensing a divergent light source." I think this is key for larger die sizes where imaging optics are becoming less efficient at producing more lux.

Fresnel reflectors and compound parabolic concentrators have some positive properties that we can probably exploit.


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## dc38 (Dec 30, 2013)

TEEJ said:


> This DOES look like my idea of reflectors angled back at the LED/Bowl to salvage more light, etc.



You means teh RLT 'tech'? nono, I have an L-Lenser which I chromed the sloping sides of the TIR to throw light forward, not 'recycle' the light XD


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## HarryN (Dec 30, 2013)

sonikaccord said:


> I've been looking at solar collectors during my search where they attempt to take advantage of the sun's surface brightness by "condensing a divergent light source." I think this is key for larger die sizes where imaging optics are becoming less efficient at producing more lux.
> 
> Fresnel reflectors and compound parabolic concentrators have some positive properties that we can probably exploit.



Well, if you would like to test some similar ideas, I have some very similar parts like this from the past that I am willing to sell. It included various sizes, types, and shapes of reflectors with various Fresnel lenses.


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## sonikaccord (Dec 30, 2013)

I may be interested, do you have a fs thread or is it better to pm me

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## sonikaccord (Jan 17, 2014)

I may have found a fresnel lens that could work. I have used imaging optics at low power and I get a cool yellow phosphor and blue image


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