# Light guides for combining multiple LEDs to a point source?



## KreAture (Nov 20, 2007)

I have been playing with diff torches and reflectors using 1-9 LEDs.
My biggest issue with multiple led is they are harder to focus.

For immense throwing distance I have been replacing the glass on some torches with lenses colaminating the beam into a 0.5-1 degree spread max. This gives incredible throwing distance but works best on a point source. Using multiple leds tend to create multiple blooms or hotspots at the target.

So, I thought, why not use lightguides!
Some sort of christmastree of 8-10mm lexxan-like material curved and melded together from each led towards a common output. Kind of BIG optical fibre. The output of the fibre could then be focused by a twist-adjusted lense at the tip for custom focus like some maglites have.

Waddya think? Anyone have equipment to try this?


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## saabluster (Nov 22, 2007)

I had the same idea. If you look hard enough you will find some information on the internet but not much. I've been working on this for about 5 months and have yet to get it to work very well. I know its possible but it will just take time to develop the right technique. If I can make it work it could be the one thing that could beat LPS for throw. It will be awhile though. Its all about surface brightness.


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## Duglite (Nov 24, 2007)

I'm really interested in this too. I'd like to be able to combine several LEDs into a single point source, and I came to the conclusion that light guides as described by KreAture would be the best way to do this. Unfortunately, it's beyond my technical ability, and an off-the-shelf device is probably waaay expensive. I'd love to know if anyone makes any progress on this.


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## KreAture (Nov 24, 2007)

OOOOh!
Look what I found!
http://spie.org/x8762.xml

Now this is exactly what I wanted to see.
It's possible, feasible and possibly not too hard to build/mold.


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## saabluster (Nov 24, 2007)

KreAture said:


> OOOOh!
> Look what I found!
> http://spie.org/x8762.xml
> 
> ...



That is a GREAT find. Only one problem. Where do we buy it? This is the problem I had. I found some neat solutions out there and they are either WAY too expensive or not even able to be bought.


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## LukeA (Nov 24, 2007)

You could put each LED at one focus of an elliptical (not parabolic) reflector, and angle the LEDs in reflectors so that the other focus of each ellipse is common and also the focal point of the lens. You will lose a good bit of light as spill from the reflectors, but you'll end up with much more light passing through a single point than by most other methods.


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## Duglite (Nov 25, 2007)

KreAture said:


> OOOOh!
> Look what I found!
> http://spie.org/x8762.xml


I never bookmarked an article so fast in my life!:goodjob:


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## DM51 (Nov 25, 2007)

Very good find indeed. 

This is obviously still pretty much at the research stage, but it isn't too hard to imagine that in only a very few years, this idea will have combined with increasing LED efficiency (= decreasing heat problems) and fiber-optic internal-reflection technology, to the stage where the output from many LEDs could be concentrated into a single tiny point.

This experiment has already worked with 3 LEDs. There is no reason to suppose that it could not in due course be done by 30 LEDs, or 300, as they won’t need to be mounted side by side as in this experiment – they could be widely dispersed, with fiber-optics bringing the light in to the single point. 

The point source is a very significant part of this – the smaller the point, the better it can be focused. 

If this happened with 30 LEDs emitting even only 200 lm each, you already have a point source of 6,000 lm. With 300 LEDs, it would be 60,000 lm…


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## KreAture (Nov 25, 2007)

Exactly DM51. There is no rules as to topology.
Injecting another light source into a fibre/lightguide is not too hard.

LukeA, using the technique you describe will let light pass through a point, but not originate from same point with any degree of colmination. The lightsource will still be big. Trying to focus it to a cominated tiny beam will be very hard.

Next time there is fog here I'll take some beamshots of my cominated 1w Cree. You'll love it. The beam is like a intense light-rod inside a dimmer tube, continuing on in the distance untill it is diffused by the fog.

I have access to some lexxan material in rods and will see if I can fuse them into some beam-combining contraption.


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## DM51 (Nov 25, 2007)

KreAture said:


> Next time there is fog here I'll take some beamshots of my cominated 1w Cree. You'll love it. The beam is like a intense light-rod inside a dimmer tube, continuing on in the distance untill it is diffused by the fog.


Sounds excellent. What lens are you using? Have you seen the other threads on aspheric lenses?


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## KreAture (Nov 25, 2007)

I haver this huuuge 4" dia lense that I use to see what effects I can get with lensing the torch. Then I look to see what f number I will need. If I am lucky I can just pick up a pair of cheap circular glasses at bestbuy or similar for $2 to fit instead of the torch original glass. (plastic lenses, easy to trim...)

I also found my local ee shop has lightguides!
http://www.elfa.se/images/highres/h10859.jpg
They come in strips of 10 and cost $1 a strip. 3mm round tips, 15, 30 or 45mm long.


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## DM51 (Nov 25, 2007)

If you have a very small point source of light, the best result will be achieved by putting the lens at a distance from it equal to its focal length. 

You can get a good idea of the focal length of a lens on a sunny day by measuring the distance from the lens at which the sun focuses into a point having passed through it. 

I'm very much looking forward to hearing about your further experiments with light-guides.


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## KreAture (Nov 25, 2007)

Jusr remembered, I havce some coctail sticks here!
They are crystal clear plastic with polished edges and triangular.

One end has sides 5x5x5mm while the other has 1x1x1mm and they are 90mm long. I bet those could be made to collect light from multiple LEDs and simply merge to a point.


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## saabluster (Nov 25, 2007)

KreAture said:


> Jusr remembered, I havce some coctail sticks here!
> They are crystal clear plastic with polished edges and triangular.
> 
> One end has sides 5x5x5mm while the other has 1x1x1mm and they are 90mm long. I bet those could be made to collect light from multiple LEDs and simply merge to a point.


I highly doubt the plastic used would be of a high enough quality to work for light transmission. The plastics used for optics is not your everyday clear plastic.


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## DM51 (Nov 26, 2007)

The main problem you will have is heat - it will melt the plastic. LEDs get very hot, so you will need glass. 

Another point is that the ideal fiber-optic configuration is a thin cylindrical tube. A tube with a triangular cross-section will be only half as efficient at transmitting light, as there are 4 escape surfaces rather than just two. The amount of light that will escape from each surface is equal. Only a quarter of the light will reach the far end of the stick, rather than half of it.


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## frenzee (Nov 26, 2007)

This is a fascinating subject. I looked at LPI's patent copy and it looks like the key to their design is an "SMS" or Simultaneous Multiple Surface optic which looks like a combination fresnel lens on one side and an asymetrical refractor type lens on the other side. Very interesting, but I still haven't figured out how it's supposed to work, but if it does work as they claim, which sounds like it does, this would be holy grail of RGB lighting and flashlight optics, not to mention automotive lighting, solar lighting, etc. I wonder why we haven't heard more about them. (I wish Google's Sci/Tech section would cover more real science like this instead of game consoles and social networking sites...grrrr). Thanks KreAture for digging this stuff up.


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## saabluster (Nov 26, 2007)

DM51 said:


> The main problem you will have is heat - it will melt the plastic. LEDs get very hot, so you will need glass.



You don't need glass. There are tons of plastic optics and plastic reflectors used with LEDs.



DM51 said:


> Another point is that the ideal fiber-optic configuration is a thin cylindrical tube. A tube with a triangular cross-section will be only half as efficient at transmitting light, as there are 4 escape surfaces rather than just two. The amount of light that will escape from each surface is equal. Only a quarter of the light will reach the far end of the stick, rather than half of it.


 
"escape surfaces" Where did you get this idea? What we are discussing would be TIR optics.


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## DM51 (Nov 26, 2007)

saabluster said:


> You don't need glass. There are tons of plastic optics and plastic reflectors used with LEDs.


 In this case the material would need to be in very close proximity to the LED surface, if not in actual contact with it. I don't think there is a plastic material that could withstand the heat involved.





saabluster said:


> "escape surfaces" Where did you get this idea?


 I think you may need to read up on how fiber-optics work. 





saabluster said:


> What we are discussing would be TIR optics.


 In fact we were talking about fiber-optics. Not quite the same thing.


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## 65535 (Nov 26, 2007)

I don't know about glass, but most plastics soften and warp around 80C so majority of them are out of the question.


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## saabluster (Nov 26, 2007)

DM51 said:


> In this case the material would need to be in very close proximity to the LED surface, if not in actual contact with it. I don't think there is a plastic material that could withstand the heat involved.


Close yes. In contact no. You would ruin the led. You would need to use an optical gel in between the LED and optic. I do know there are plastics that can handle the heat. I work with plastics all the time prototyping and molding my own parts.




DM51 said:


> I think you may need to read up on how fiber-optics work.


I know exactly how they work. You still did not answer the question. 



DM51 said:


> In fact we were talking about fiber-optics. Not quite the same thing.


Fiber optics use TIR. The 3 LED combiner we were talking about is a TIR optic. It is made from plastic.


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## DM51 (Nov 27, 2007)

saabluster said:


> Close yes. In contact no. You would ruin the led. You would need to use an optical gel in between the LED and optic. *I do know there are plastics that can handle the heat. *I work with plastics all the time prototyping and molding my own parts.


 That is very interesting. Plastic would certainly be a great deal easier to work with, if it can handle the heat.





saabluster said:


> I know exactly how they work. You still did not answer the question.


 Light escapes equally from each surface. A cylinder has 3 surfaces – one at each end, and one cylindrical-shaped surface along its length. One end is the input for the light. Half of the light will escape equally from the other two, so allowing for absorption and other inefficiencies, approaching 50% comes out of the other end of the fiber-optic, almost irrespective of its length.

A filament with a triangular cross-section, such as the cocktail sticks, has 2 additional surfaces, so the internal reflection would only be half as efficient.





saabluster said:


> The 3 LED combiner we were talking about is a TIR optic. It is made from plastic.


 I think we may be talking at cross-purposes. I was discussing combining the output of many more than 3 LEDs, but the principle would be the same.


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## saabluster (Nov 27, 2007)

DM51 said:


> Light escapes equally from each surface.



TIR = Total internal reflection. It works by not allowing light to escape until you want it to. Its not about how many sides it has.


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## DM51 (Nov 28, 2007)

I know what TIR stands for. However in applications discussed in CPF, it usually refers to optics where the LEDs / other light sources are positioned facing backwards, so that none of the light escapes directly through the front on the lens, but is instead pointed back into the reflector. All the light is gathered by the reflector and by this method it is collimated more accurately and efficiently. There is an interesting thread somewhere in which Ra shows a ~95% efficient optic of this type. 

Are you saying that a fiber-optic with a triangular cross-section will be as efficient as a circular one?


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## saabluster (Nov 29, 2007)

DM51 said:


> I know what TIR stands for. However in applications discussed in CPF, it usually refers to optics where the LEDs / other light sources are positioned facing backwards, so that none of the light escapes directly through the front on the lens, but is instead pointed back into the reflector.


 I don't think it usually refers to backwards facing LEDs. I have seen quite the opposite here. The ones in Inovas and Coast flashlights(just to name a couple) are not back facing. And all of the ones that I have seen for sale on Cutter, DX, and the like are all normal LED facing forward designs. Not trying to fight this is just what I've seen. 


DM51 said:


> Are you saying that a fiber-optic with a triangular cross-section will be as efficient as a circular one?


 To be honest I don't know. I doubt it would be AS efficient but I don't see there being a huge difference. Just a guess. I haven't seen any papers on it. I doubt there would be much information on this as it would seem very difficult to manufacture(having seen a show on how fiber optics are made). If you know of some research into this please provide a link. I'm always ready to learn more.


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## DM51 (Nov 30, 2007)

Interesting discussion. I don't know the lights you mention. The optic that caught my attention was the one Ra made - I'd like to be able to give you a link to that thread, and will try to find it.

I am 95% sure about this business of the 'escape surfaces' (or whatever the tech term is) but you seem to be quite knowledgeable and your posts have given me cause to question my assumption. I can't remember where I read about this, but I will try to find some reference material. Likewise, if you find anything, please let us know. 

This is an extremely interesting subject, and the further development of TIR/fiber-optic technology has huge potential for us.


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## Sub_Umbra (Nov 30, 2007)

KreAture said:


> OOOOh!
> Look what I found!...
> http://spie.org/x8762.xml


That's interesting. The idea of feeding an LED 'combiner' into an *undershot parabolic reflecter* is overdue. _Any_ undershot recoil design will *greatly reduce* spill coming out of the combiner.

I think the parabolic reflecter is used with the combiner to unify the mess that comes out of it. When I first read the Subject line all I could think of was the Lumaray lights with arrays where each LED must be focused by hand at the time of manufacture. With the inherent variation from LED to LED in current manufacture, the combiner/reflector combo is a great idea to cut labor costs in assembly. It's a great idea. 

I was trying to get people interested in Recoil lights with undershot parabolic reflectors in *this thread* back in early 2004.


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## KreAture (Nov 30, 2007)

Thanks for the interest ppl.
As for the actual plans I can tell you I feel some haven't grasped it.
The angle that light strikes an internal surface in a lightguide must be lower (relative to the surface) than the TIR-angle. If it is, you get reflection with little or no loss. Almost all clear materials have this angle, but it varies. Depending on the material you also get losses in transmission from absorption in the material itself. However, the goal is to add as much light as possible to a single point to give an apparant higher prightness. This will be doable regardless of losses.

I have been playing around with my coctail sticks but haven't had time to polish em up after joining the tips with Acrifix. (Acrylic glue.)
I have tried shining light into the 5 bases and I do indeed see the light being guided up to the tips and combined into a brighter and smaller area than the emitting led's. (The sticks are tapered so they do this naturally.)

I use a laser to test the scattering/leakage and it gives a good idea at where light will leak relative to the input angle. Dunno if anyone has done this before, but I just found it the simplest way.

I do have an idea for a lightguide for collecting light from multiple luxeons without making a very long torch. It's a quite "out of the box"-thinking design, and I'll post a picture here when I have finished the prototype. It should be possible to make at home. Atleast a rough proof of concept.

Right now I am looking for software that can help me analyse refraction-paths based on cross-sectional cad-drawings of optical paths.
I tried the demo of OpTaliX and it's horrible.
What is needed is something that will allow me to combine freehand and defined shapes in a 2D environment and test. 3D tests will be nice but I can survive with 2D.


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## KreAture (Nov 30, 2007)

OOOOh!
I just had another brainfart!

Imagine you make your lightguide but find you can't get it optimal in size if you have to adhere to the TIR angles. What do you do ?
Well, if your lightguide has an optical finish why not just coat it with a reflector! It just hit me. I think using this could let me complete my odd lightguide in even less space!

Just a thought...


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## KreAture (Nov 30, 2007)

We have FOG!
Wohooo. There was fog the other day and I took some pics. Not really relevant to this thread but it shows the diff between just a reflector and a carefully colminated beam...
Images were taken by hand so there was some movement in beam and cam. However, the principle is visible.
http://kreature.dynu.com/ee/led/1w_cree_normal.jpg
http://kreature.dynu.com/ee/led/1w_cree_lensed.jpg

Remember, you can't see the entire beams due to difraction angles in the water droplets making up the fog. Without the fog I can project the image of the LED with reflector over 500ft. This is a 1w torch btw...


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## LedLad (Nov 30, 2007)

hmmm....interesting discussion....For my $.02 ...I worked with plastics for many years and contrary to what seems to be popular opinion there are types of plastics which have very high transparency and are VERY resistant to heat...the best I think would be polycarbonate. I havent worked in the field in years but I would nearly bet that a simple internet search would come up with a source for cheap polycarb 'rods' which might be perfect for this app. On another note ...I'm not sure that you're going to see the gains you might expect with something like this since every time a beam of light passes from one medium to another there are major losses...

emitter/air to light guide Loss 1 +
light guide to air Loss 2 +
Air to combiner/optic Loss 3 =


Just my $.02


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## saabluster (Dec 1, 2007)

KreAture said:


> The angle that light strikes an internal surface in a lightguide must be lower (relative to the surface) than the TIR-angle.


You are absolutely right. This is key.

I guess I haven't been forthcoming on some of my ideas. But I really would like to see this move forward and I could use help from you guys. Here is a drawing of the basic idea that I have.
You would need to remove the glass dome on the Cree LED so that the fiber optic could get as close as possible. Interestingly enough you would need optical gel to get the light in the fiber optic and the cree comes ready made in that regard. The gel is just under the lense. So just press the fiber optic up against the gel.

The little plastic barrel you see is the top of a pencil that just so happens to fit perfectly over the metal ring on the cree. The hole in the top allows the fiber optic to pass through and will hold it in place over the LED die(with appropriate mods which I don't feel like going into now). Then the many fiber optic leads would all be sent to the Fiber Optic Taper. That in turn could be collimated with an aspheric for unbeliveable throw. This design should allow for a decent percentage of the light output from the LEDs to make it to the Aspheric. This could be WAY better than Low pressure sodium for throw. 

The problem? Look at the price of the Fiber optic taper. These are used in many devices so we might be able to find something we could scavenge one out of. Second problem is finding one with a small 1mm or less output size. If we can overcome this though we could be building the craziest flashlights this world has seen. Imagine a small EDC with the throw of a large spotlight.


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## saabluster (Dec 1, 2007)

LedLad said:


> On another note ...I'm not sure that you're going to see the gains you might expect with something like this since every time a beam of light passes from one medium to another there are major losses...
> 
> emitter/air to light guide Loss 1 +
> light guide to air Loss 2 +
> ...


 True. But thats why you use optical gels. It keeps this from happening.


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## KreAture (Dec 1, 2007)

saabluster, that wasy my original idea too.
Then I thought why not twist the entire design up a bit...

Here's my first prototype without any angles clauclated. It still shows the basic idea.






I shine a laser into the bottom right peg on this image.
In theese I shine into the diff pegs in sequence:
http://kreature.dynu.com/ee/led/guide1_2.jpg
http://kreature.dynu.com/ee/led/guide1_3.jpg
http://kreature.dynu.com/ee/led/guide1_4.jpg

As you can see, the angles are all off, but it was not that difficult to cut.
If I can get Zemax or similar app to aid me in adjusting the angles I think this could work well. If one coated it with reflective silver-laquer or somehting it could reduce leakage even further. I do switch the direction of light vs layout of torch but I thought it's about time someone decided a torch doesn't have to be long, thin and circular.

I used regular lexxan, polished up to something shiney.


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## KreAture (Dec 1, 2007)

This looks very expensive btw, and requores colminated light to work:
http://www.lambda.cc/PAGE268.htm


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## saabluster (Dec 2, 2007)

KreAture said:


> If one coated it with reflective silver-laquer or somehting it could reduce leakage even further.


Lacquer based anything will not work. Nothing you could go buy at the store will work. It will only make it worse. It would need to be coated with a thin layer of metal such as is done for flashlight reflectors.


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## saabluster (Dec 2, 2007)

KreAture said:


> I used regular lexxan, polished up to something shiney.


I like this idea. I've got a whole 4x8 sheet of clear acrylic to play with.:thumbsup:


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## KreAture (Dec 2, 2007)

I was talking about metallizing, but varnish/laquer was the only word I could think of. It would help in the reflection though, and allow sharper angles than otherwise possible. This would reduce the size of the combiner.

Having some silver-paint lying around I decided to coat the top of my prototype. It's drying now. I don't expect any improvement. IN fact I think it will kill the TIR.


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## nein166 (Dec 2, 2007)

Instead of trying to paint or adhere a reflective surface could you put a reflective sheet like mylar against the curve with the optical gel in between.

I thought about the fiber optic system as well, but I was going to use the optic injectors to get the light into the fiber optic cable then bundle them all together behind the aspheric in a ziptie or the like. I saw the injector on Cutter.com.au The pen cap idea seems more compact, one could easily put 6 cree side by side and make an extreme point source of light. Put that all on a heatsink in the body of a mag just above the switch behind a 52mm aspheric and you got a retina scorcher!


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## KreAture (Dec 6, 2007)

I haven't gotten much further as I can't seem to find a simple program to simulate the angles for TIR for me. The apps are either overly complex and expensive or only handles simple lenses.

It looks like the shape I need could fit within approx 1" high space making for quite an oddly shaped light. If I place the LED's and lightguide standing there would be room for two 18650's next to it in a square-ish housing. First I'll have to get the lightguide right. I'll try using something reflective but do not have any gel... Anything I might have that can do the job?

As for polishing, I have "sandpaper" in 150, 300, 600, 800, 1200, 2400 and 4800 grit as well as polishing agent for plexi/lexxan so I can get the surfaces really nice and clear. The higher grades aren't really what I'd call sandpaper. It's after all finer grit than regular printing paper and used for finishing polish on manual optical fibre termination by those insane enough.

On a sidenote I got a XR-E Q4 WG to play with


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## DM51 (Dec 6, 2007)

Polishing will be THE major problem - the slightest imperfection, even a microscopically small one, will create a node for light to escape. I'm not sure how this problem can be surmounted.


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## KreAture (Dec 6, 2007)

Actually, you need a quite sharp imperfection before it becomes a problem. The polishing process I use smoothes out minor flaws very well causing only slight changes in angle on a otherwise smooth surface. (As seen from the lights perspective ofcource.)
As you can see in my laser-tests the major leaks I am having are due to internal angles. Filing down the corners and polishing up should reduce the edge glare you see.


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## saabluster (Dec 6, 2007)

KreAture said:


> As for polishing, I have "sandpaper" in 150, 300, 600, 800, 1200, 2400 and 4800 grit as well as polishing agent for plexi/lexxan so I can get the surfaces really nice and clear.


Glad to see your still working on it. As for polishing the edges I find that after sanding to remove the ridges you can run a mini torch along the edges to "polish" the edges. Your way works just fine but this might save some time.


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## frenzee (Dec 7, 2007)

I got in touch with LPI to see if they can give us some samples to test their collimator concept (fingers crossed). I was pleasantly surprised to get a personal email back from the preseident in response to my inquiry. He said they license their technology exclusively to a couple of flashlight manufacturers (no one I had heard of before). Interestingly, when I checked out their websites, I couldn't find a single flashlight that used LPI's so-called SMS folded collimator. Well anyway, I am waiting for hear back rignth now. I can't wait to put this thing to the test with three Crees or Rebels.


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## KreAture (Dec 7, 2007)

Yeah. But I still wany 6+ not 3 LEDs...
Anyone know of any software that will easily allow me to CAD some simple 2D or wireframe shapes to simulate TIR lightpaths?
So far I have tried Zemax and Oslo and they are both almost identical and both terrible. They are more for optics like lenses than lightguides and designing curves like we need seems mayhem in them both.

Theres gotta be a simple tool that will allow us to join diff shapes to form a 2D path. 2D would be enough to start off with and NO I am not sitting down with tracingpaper...


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## saabluster (Dec 19, 2007)

KreAture said:


> Right now I am looking for software that can help me analyse refraction-paths based on cross-sectional cad-drawings of optical paths.


Looky what I found. It would appear to be the very program used to make that 3 LED combiner.


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## saabluster (Dec 19, 2007)

KreAture said:


> If I can get Zemax or similar app to aid me in adjusting the angles I think this could work well..


 I reread all the posts and just noticed you mentioned Zemax already.


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## KreAture (Dec 19, 2007)

The user interface was horrid and the demo wouldn't allow me to change anything.


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