Focussing multiple LED's Theory

[jashhash]

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.

 

[Mike Painter]

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.

 

[saabluster]

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?

 

[jashhash]

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.

 

[Gomer]

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.

 

[2xTrinity]

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.

 

[Gomer]

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

 

[Jaz]

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.

 

[uk_caver]

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?

 

[uk_caver]

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.

 

[jashhash]

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:

 

[Mike Painter]

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.

 

[jashhash]

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

 

[2xTrinity]

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

 

[uk_caver]

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.

 

[SemiMan]

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

 

[uk_caver]

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?

 

[VidPro]

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.

 

[VidPro]

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.

 

[TMorita]

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