# Focussing multiple LED's Theory



## jashhash (Apr 16, 2008)

I came up with this idea today and was wondering if it would be possible to concentrate a beam of light using multiple LED's. The diagram explains how this could potentially work. If it were possible to use this double lense setup this could potentially help overcome the problems that LED's have with throw. Imagine a true LED 1 million candle power spotlight.


*Update*









These models further illustrate what I'm trying to accomplish. The benefit of combining beams of several LED's is that you get a much more intense spot light without sacrificing throw.


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## Mike Painter (Apr 17, 2008)

It would be expensive and difficult to maintain.
I'm still convinced a good Fresnel lens would be best. They can take a kerosine latern flame and throw it 20 miles.


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## saabluster (Apr 17, 2008)

jashhash said:


> the problems that LED's have with throw.


Well I really don't feel LEDs have a problem with throw.


As to your idea I am not an expert on optics yet so I don't know if it would work. I have my doubts that's for sure. I tried a quick test of your idea and could not get it to work not that it means anything. Have you tried to make a mock-up and test your idea?


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## jashhash (Apr 17, 2008)

Im not sure if this idea would work either, Since I'm not an expert, I was hoping that somone who is an expert might comment. If you can figure out another way to throw an LED beam like an HID that would be awesome.


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## Gomer (Apr 17, 2008)

Without going into ray tracing, you will not be able to columnate quite how you drew it. Also, to a first approximation, every glass/air interface will have a 4% loss at best just from solving normal incident Fresnel equations.. You have 4 interfaces so you are looking at 0.96^4 or 85% power transmitted in the absolute best case scenario. This is one reason why high polished reflectors are nice. You can get 98% mirror finishes without too much trouble.


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## 2xTrinity (Apr 17, 2008)

Gomer said:


> Without going into ray tracing, you will not be able to columnate quite how you drew it. Also, to a first approximation, every glass/air interface will have a 4% loss at best just from solving normal incident Fresnel equations.. You have 4 interfaces so you are looking at 0.96^4 or 85% power transmitted in the absolute best case scenario.


I know a lot of the aspheric lenses used for flashlight mods are AR coated on both sides.



> This is one reason why high polished reflectors are nice. You can get 98% mirror finishes without too much trouble.


Doesn't look like any exist in the flashlight community. Want to know why only 2/3rds of the bubl lumens from incan flashlights actually make it out as torch lumens (confirmed experimentally numerous times), efficiency of real-world aluminized reflectors is somewhere around 65% :green:

Good TIR optics, with AR coated interfaces could well exceed 95% total efficienc, if only we had some good ones available.


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## Gomer (Apr 17, 2008)

If you get bored, it might be worth modeling up in OSLO.


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## Jaz (Apr 17, 2008)

jashhash said:


> Im not sure if this idea would work either, Since I'm not an expert, I was hoping that somone who is an expert might comment. If you can figure out another way to throw an LED beam like an HID that would be awesome.


 
I'm not an expert either, but I've experimented a little with some lenses and my Fenix L2D, and got a pretty impressive result with a lens of about 6cm diameter, the largest I've tried. It increases the throw 10-15 times and creates an almost laserlike beam that's very visible in the night air. 
The best way to get lots of throw is I think to use a big lens with the right focal length, so you can place the lens as far from the LED as possible (the distance has to be the same as the focal length to get maximum throw) while still catching most of the spill, which is what gets concentrated into the beam (the hotspot's light gets directed off to the sides).
I don't think your idea would work as you're thinking it might; you'd be better off just using lens no. 3. Lenses 1 & 2 would (I think, I'm not sure) have a negative effect.

Edit: Oh, sorry, I wasn't thinking properly and forgot about the multiple LEDs part, which I guess is the whole point. I think you'd still get the same or better throw with one led (between where no. 1 and no. 2 are) and one lens, it just wouldn't cover as wide an area.


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## uk_caver (Apr 17, 2008)

Looking at the original drawing:
First, unless lenses #1 and #2 are wider/closer to the emitters, they'll be missing out on a lot of the light.
Second, if lenses #1 and #2 spread their light out on lens #3, the resulting beam might have two blotches in it, rather than being circular.

From an optical point of view, within limits of cost, alignment precision and size, I'd wonder if it is actually possible to get a lens 1/2 +3 combination giving a better spot beam than using individual single lenses (or maybe individual twin lenses?).
That is, for a given amount of money, is it easier to focus light to an accurate spot than into an accurate parallel beam?

If a smaller emitter tends to give a tighter beam with a given-sized lens, would a Rebel be the best source for a serious spot beam?


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## uk_caver (Apr 17, 2008)

Actually, thinking again, what the arrangement seems to be is a pair of twin-lens systems, with the second lens of each pair happening to be a section of a large lens.
I'm not sure that would be likely to give a benefit over an inline system with two smaller second lenses.


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## jashhash (Apr 17, 2008)

yes this setup would have to be extremely precise. If you remember back to the times of the Luxeon 5's, and how most people wouldnt want to use them because the large die size made for an unfocusable beam, so the result was an extremely bright wall of light. I know there would be a lot of losses in efficiency with the beam passing through 2 lenses but since LED's are becoming so efficient that's not really the issue. The issue is that I want a really intense straight beam of light without using a huge 5" lense. I'm thinking of something like this:


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## Mike Painter (Apr 17, 2008)

jashhash said:


> yes this setup would have to be extremely precise. If you remember back to the times of the Luxeon 5's, and how most people wouldnt want to use them because the large die size made for an unfocusable beam, so the result was an extremely bright wall of light. I know there would be a lot of losses in efficiency with the beam passing through 2 lenses but since LED's are becoming so efficient that's not really the issue. The issue is that I want a really intense straight beam of light without using a huge 5" lense. I'm thinking of something like this:



I think that we are going to have to ask exctly what you want to do with this light? 

Something like  this is probably as good as you will get without a lot of work and expense. I think it would appear as one beam after a few feet at most.


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## jashhash (Apr 17, 2008)

Hold On I'm creating a solidworks model that will hopefully better clarify what I want to do.


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## 2xTrinity (Apr 18, 2008)

I just thought of what this sort of optics setup would be perfect for -- an RGB, or RAGB* array with perfect color mixing. Or for that matter if oyu wanted to, you could experiment with say mixing three whites with a red to improve color rendition, or all sorts of things, and it will all "look like" one point source.




A = Amber, not necessary for monitors, but helps with color rendition if you use it in a flashlight


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## uk_caver (Apr 18, 2008)

I'm not sure it would be any better for colour mixing than independent parallel lens/optic/reflectors systems.
The different-coloured light would still be coming from different areas of the main lens, and if the final beam really was parallel-sided, the colour would vary across the beam. If the final beam diverged significantly, then parallel beams from separate optical systems would probably blend about as well within a reasonable distance.


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## SemiMan (Apr 18, 2008)

uk_caver said:


> I'm not sure it would be any better for colour mixing than independent parallel lens/optic/reflectors systems.
> The different-coloured light would still be coming from different areas of the main lens, and if the final beam really was parallel-sided, the colour would vary across the beam. If the final beam diverged significantly, then parallel beams from separate optical systems would probably blend about as well within a reasonable distance.



There is also the issue of different source sizes for the different LEDs, i.e RED, Blue with Phosphor (white), Blue, etc.

That said it is not completely crazy and has already been done.... http://www.fraen.com/pdf/Fraen_Corporation_Sheds_New_Light_on_Mysterious_Mona_Lisa.pdf I used to have a picture of the optics design, but I remember it being similar to this concept.

Semiman


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## uk_caver (Apr 18, 2008)

With the Mona Lisa, there's significant divergence in the beam, and having different effective source positions for different-coloured LEDs wouldn't seem likely to matter.
With relatively wide-angle beams, having sources with independent adjacent optics could still give even lighting on the target.

In fact, if you know _how far away_ a target is going to be, it's not even a case of having parallel diverging beams separated by tens of millimetres, and hoping that there won't be any visible imbalance due to the offset, since it'd be possible to tilt the individual beams in so that the beam centres were identical?
Presumably the same would be possible with a single big final lens - the setup would be tweaked such that the different sources weren't firing through precisely the same point, but would be offset slightly such that their light would land in precisely overlapping patches?


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## VidPro (Apr 18, 2008)

the inital hotspot of converged light would be aquired by the first aspherical lens getting FAR from the led (to achieve the focus close). so lens selection would be critical, it would have to be a very low focal point

a converged telescope, is what you need, the led could be right against the diopter, just like the eye would be? 
doesnt a simple telescope use a concave lens (not magnifyer) to concentrate the light to the front magnifyer? i dono , but now i cant get this one back together, oops.

if you have binoculars, or even cerial box telescope, try putting a raw led right up to the eyepiece, you'll see, its like a white lazer, its a bit dim, so you need to be in the dark to see it., or even a cameras zoom lens.


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## VidPro (Apr 21, 2008)

ya know, in a morning i thought about this, and it dawned on me, that it would never be like that?
the big ball of light will never magically form in the shown focal point, because there is nothing that it hits.

each of the beams projected out of the first lens, will CONTINUE on the path they are travelling on, even if there is a tight collision point. 
so each of the beams will shoot to the outsides of the second lens.

without the big converged ball of light point, the second lens isnt projecting anything, there is nothing at the converged focal point, just beams passing on through. the picture caused me total confusion.

but i still couldnt wrap my head around a solution.
a compound lens, or a reflector, a cone or anti cone reflection.
something like a concave (aniti-magnifying) lens would have to be used around the focal point to get a new bent light starting point for the next lens. without bending the light into the second lens, it wont be going into the second lens correctally.

how about a triangle of mirrors,at the focal point, aimed so the light from the lower beams, bounces the light striaght up into the top lens. the light would just be "glancing" off of almost vertical mirrors, to get there.


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## TMorita (Apr 21, 2008)

Mike Painter said:


> I think that we are going to have to ask exctly what you want to do with this light?


 
Look at his avatar. Looks like Darth Vader...

Toshi


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## 2xTrinity (Apr 21, 2008)

> how about a triangle of mirrors,at the focal point, aimed so the light from the lower beams, bounces the light striaght up into the top lens. the light would just be "glancing" off of almost vertical mirrors, to get there.


Good idea, like this:







This compound prism setup is what color video cameras use to decompose incoming images into RGB. Something this this would certainly work "in reverse" for mixing of RGB light sources, such as LEDs, into a single beam.


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## uk_caver (Apr 21, 2008)

I guess it could mix a single red, green, and blue source together.

However, I was wondering whether if you had multiple sources of a single colour, to be able to mix them with such a system, would an optical setup capable of combining sources before passing through the prism be good enough to do the whole beam-combining job without needing the prism?


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## liveforphysics (Apr 24, 2008)

Jashhash- You have an impressive understanding of optics, and I think this method will work. All light hitting the final optic that originates from the focal point should exit columated together. If you could get a large enough final aspherical, you could fit a cluster of 7 LEDs down below, which could yeild a 2000 lumen columated projection beam. You could even make sure to clock the position of the dice to ensure you had a 28point star projected, which would look like a circle rather than a giant square.

Great work! Nice CAD work!

Best Wishes,
-Luke


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## liveforphysics (Apr 24, 2008)

Jashhash- You have an impressive understanding of optics, and I think this method will work. All light hitting the final optic that originates from the focal point should exit columated together. If you could get a large enough final aspherical, you could fit a cluster of 7 LEDs down below, which could yeild a 2000 lumen columated projection beam. You could even make sure to clock the position of the dice to ensure you had a 28point star projected, which would look like a circle rather than a giant square.

Great work! Nice CAD work!

Best Wishes,
-Luke


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## uk_caver (Apr 24, 2008)

How much better is the beam going to be in terms of collimation or 'lumpiness' than if just using an aspheric per LED?

In terms of collimation, isn't the setup equivalent to a set of lens pairs, the first focussing light to a [near] point (a patch the size of the original LED?), and the second refocussing that light into a [nearly] parallel beam.
Does that setup work better than using a single lens (ie is it somehow optically equivalent to using a relatively larger single lens, or something like that)?
Optically speaking, is there some gain from having the second lens being an area of a larger lens, rather than just a small lens?


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## LukeA (Apr 24, 2008)

uk_caver said:


> How much better is the beam going to be in terms of collimation or 'lumpiness' than if just using an aspheric per LED?
> 
> In terms of collimation, isn't the setup equivalent to a set of lens pairs, the first focussing light to a [near] point (a patch the size of the original LED?), and the second refocussing that light into a [nearly] parallel beam.
> Does that setup work better than using a single lens (ie is it somehow optically equivalent to using a relatively larger single lens, or something like that)?
> Optically speaking, is there some gain from having the second lens being an area of a larger lens, rather than just a small lens?



It should end up focusing the light from all the emitters into an area roughly the size of one die, and then throw all that light with the large lens.

SolidWorks has better rendering capabilities than anything Autodesk makes.


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## uk_caver (Apr 24, 2008)

LukeA said:


> It should end up focusing the light from all the emitters into an area roughly the size of one die, and then throw all that light with the large lens.


Yes, but even though the beams should ideally overlap in a one-die-sized spot, what would then happen is each beam carries on to its own (nonoverlapping?) section of the large lens. (I *think* the geometry means that beams will each end up passing through their own section of the main lens).

I'm just curious as to what, optically speaking, makes using a chunk of a large lens as a secondary lens a better move than using an individual dedicated second lens for each LED, or not using a secondary lens at all, but just an initial one-stage collimating optic.

There may well be advantages - I'm no optical expert - but I'd just wonder what they may be.


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## frenzee (Apr 25, 2008)

I wish your design would work, jashhash. It would solve a LOT of problems. But unfortunately I don't think it will because of inefficiencies, not in the lenses themselves, but in the LED-to-Lens path. An LED is not a point source, so no matter what optics you use, you can never get back to a point source at the other end because it is not a matter of optics - it is a violation of the entropy law. Secondly, you can never get all the light coming out of the dye to go into the lens, any lens, no matter where or how you position it. Furthermore, at least in theory, you can't "combine" two light rays, unless they have different polarizations and LED light is not polarized. The most promising development I have seen in the vein of what you are trying to accomplish was discussed in this thread:

http://candlepowerforums.com/vb/showthread.php?t=180770

I tried to get some samples from LPI, the company that makes and holds the patents on the "light combiner", and do some testing with LEDs and post the results here, but they weren't very, let's say enthusiastic.


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## uk_caver (Apr 25, 2008)

Could I clarify something?
It is possible to focus an image of an LED to be smaller than the LED, in the same way that it's possible to focus an image of the sun to be a lot smaller than the sun.

However, is it the case that the way the geometry works, the image can't have a greater point intensity than the source, or something like that?


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## GalvanickLucifer (Apr 25, 2008)

When I first saw the title of this thread, I thought maybe it was going to be about using something similar to phased-array radar to focus multiple LEDs. Would something like that even be possible with light? Now that would be cool - focusing a beam without optics!


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## lyrrag (Apr 25, 2008)

Wow you think like Nikolai Tesla. Great idea.

lyrrag


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## clint999 (May 3, 2008)

*Im not sure if this idea would work either, Since I'm not an expert, I was hoping that somone who is an expert might comment. If you can figure out another way to throw an LED beam like an HID that would be awesome.*


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## saabluster (May 4, 2008)

clint999 said:


> *Im not sure if this idea would work either, Since I'm not an expert, I was hoping that somone who is an expert might comment. If you can figure out another way to throw an LED beam like an HID that would be awesome.*


Is there an echo in here?


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## Sub_Umbra (May 4, 2008)

I think it's far more possible than not. Lumaray has done a bang up job of focusing arrays of 5mm LEDs running at their sweet spot into tight, efficient beams. There would seem to be no reason why this can't be applied to higher powered devices. Look at the *LumaRay FL6-2006.* I think the biggest impediment to building a higher powered version is inertia..._for the most part._ The cheap imported 'showerheads' are giving hi-tech arrays a bad name.


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## snarfer (May 4, 2008)

I think this patent application is of relevance:

Isotropic collimation devices and related methods
[SIZE=-1]US Pat. App 11/370,395 - Filed Mar 7, 2006 - Luminus Devices, Inc.


[/SIZE]


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## uk_caver (May 5, 2008)

Sub_Umbra said:


> I think it's far more possible than not. Lumaray has done a bang up job of focusing arrays of 5mm LEDs running at their sweet spot into tight, efficient beams. There would seem to be no reason why this can't be applied to higher powered devices.


Are the Lumarrys effectively the same as the various multi-high-power-emitter torches - running parallel beams and relying on the LED/focussing units being closer together than the spread of the beam at a reasonable distance, meaning the beams effectively overlap?


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## Sub_Umbra (May 5, 2008)

uk_caver said:


> Are the Lumarrys effectively the same as the various multi-high-power-emitter torches - running parallel beams and relying on the LED/focussing units being closer together than the spread of the beam at a reasonable distance, meaning the beams effectively overlap?


Yes. In the FL6 each LED/lens is focused individually at assembly time for one very tight, throwy beam. Because the small LEDs are running at their sweet spot the beam is produced with less juice than a single higher powered emmiter would require for the same output. (The FL12 has six 5mm LEDs arranged behind lenses just like the FL6 but it also has 6 more 5mm LEDs without lenses clustered tightly in the center for a more floody beam.)


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## jashhash (May 5, 2008)

I'm having some serious doubts about this theory right now too... For some reason I'm not willing to throw in the towel just yet. I wish there were some cad program out there somewhere (like solidworks) which could correctly calculate the physics of light reflection. I wish I could build an actual working model but I just dont have the cash to drop a couple thousand just to make a test rig.

Edit:


It seems there is a cad software capable of calculating light reflection if optics: http://www.motorsportsengineering.org/automag/cad/10.htm


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## 2xTrinity (May 6, 2008)

Sub_Umbra said:


> Yes. In the FL6 each LED/lens is focused individually at assembly time for one very tight, throwy beam. Because the small LEDs are running at their sweet spot the beam is produced with less juice than a single higher powered emmiter would require for the same output.



If you look at the analysis in the white LED lumen testing thread, the sweet spot for most 5mm LEDs is around ~5mA with a peak efficiency of generally no higher than 100 lm/w (ie, the Nichia GS) Run a Cree R2 or Rebel 100 at 30mA (5mA * 6) and it will be running at its exact sweet spot, producing 150 lumens per watt. Even with TIR with 20% losses, the high power LED woudl be ahead for lumens. Although the 5mm LEDs will certainly be cheaper.


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## Sub_Umbra (May 7, 2008)

2xTrinity said:


> If you look at the analysis in the white LED lumen testing thread, the sweet spot for most 5mm LEDs is around ~5mA with a peak efficiency of generally no higher than 100 lm/w (ie, the Nichia GS) Run a Cree R2 or Rebel 100 at 30mA (5mA * 6) and it will be running at its exact sweet spot, producing 150 lumens per watt. Even with TIR with 20% losses, the high power LED woudl be ahead for lumens. Although the 5mm LEDs will certainly be cheaper.


While I haven't done the math I believe you're probably correct _at this time._ It was true when the FL6-2006 came out as it's CS LED array out performed the LuxIIIs available at the time. That was one of the ideas behind the light. LuxIIIs were all there were to compare it to.


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## Data (May 10, 2008)

jashhash, As you have the drawing done the diameter of the final beam will not be smaller than if you had just gone straight out of each LED/lens. As was pointed out the LumaRay is a good example. I have a LumaRay and love the light it puts out. I also think you may want to look at my DB-70.

Say the collector lens #1 is the one by each LED and collector lens #2 is the final lens that the light from each LED( and #1 lens) ultimately passes through.

Now if your goal was to make the output diameter smaller than the array of LED's it could be done if you scale down the lens #2 and bring it closer to the multi-focal-point.

Having said that you are going to find the ratio of LED die size to aspheric collector #1 diameter is a big issue and may drive the overall size of this device. I used 25mm lenses in my DB-70 design. The resultant individual beam diameter is larger than if I had used a 40mm lens. If I had used lenses as small as you depict in your drawing the light coming out would not be very collimated.


Cheers
Dave


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## Gomer (May 10, 2008)

jashhash said:


> I wish there were some cad program out there somewhere (like solidworks) which could correctly calculate the physics of light reflection. I wish I could build an actual working model but I just dont have the cash to drop a couple thousand just to make a test rig.



Try out Oslo
http://www.sinopt.com/

THere is a free demo version


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## uk_caver (May 11, 2008)

Data said:


> ...
> Now if your goal was to make the output diameter smaller than the array of LED's it could be done if you scale down the lens #2 and bring it closer to the multi-focal-point.


If the second lens is smaller, and closer to the patch of space where the beams from the LEDs cross, wouldn't that make it harder to get a tight beam?

Even if the 'starting size' of the beam (the lens diameter) is smaller, in terms of beam angle isn't the geometry of the setup similar to having the original larger lens focussing light from a larger patch of space, which would give a more diverging beam?
If so, presumably there'd be some distance where having a narrower-angle beam from a larger lens would give a tighter spot than a more diverging beam from a smaller lens?


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## LukeA (May 11, 2008)

uk_caver said:


> If the second lens is smaller, and closer to the patch of space where the beams from the LEDs cross, wouldn't that make it harder to get a tight beam?
> 
> Even if the 'starting size' of the beam (the lens diameter) is smaller, in terms of beam angle isn't the geometry of the setup similar to having the original larger lens focussing light from a larger patch of space, which would give a more diverging beam?
> If so, presumably there'd be some distance where having a narrower-angle beam from a larger lens would give a tighter spot than a more diverging beam from a smaller lens?



Yes, starting about 5-10 feet from the thing.


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## Data (May 11, 2008)

uk_caver said:


> If the second lens is smaller, and closer to the patch of space where the beams from the LEDs cross, wouldn't that make it harder to get a tight beam?
> 
> Even if the 'starting size' of the beam (the lens diameter) is smaller, in terms of beam angle isn't the geometry of the setup similar to having the original larger lens focussing light from a larger patch of space, which would give a more diverging beam?
> If so, presumably there'd be some distance where having a narrower-angle beam from a larger lens would give a tighter spot than a more diverging beam from a smaller lens?




I agree with you totally.


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