Help needed with a LED project
Help needed with a LED project
(OP)
Being new to this forum I hope I place the question in the right place.
I am currently involved in the design of a power LED searchlight. The requirement is 4 lux at 200 meters with a 5-6 deg. beam (+/- 2.5-3 deg.)
While LED and LED systems is what I do for the last 13 years, I never attempted to work on something with such a narrow beam at this intensity.
First I would like to know if somebody has any experience with such optics.
Second, it will be interesting to hear opinions about the single vs. multiple sources to match this intensity.
There are plenty of COB (chip on board) arrays available providing more than enough lumens, however the optical designers hate to work with them as they are far from being the ideal "point source".
From the other point, working with multiple sources each with it's own optics is also considered by some non practical, they claim the total power from several light sources all pointed to the same direction will be much less than the same power emited from a single source !? Is this true?
The smallest emitter I managed to get is 11.5mm diameter with an output of 1330 lumen at 17W. Why is it so hard to design a narrow beam optics?
Any input will be highly appreciated.
I am currently involved in the design of a power LED searchlight. The requirement is 4 lux at 200 meters with a 5-6 deg. beam (+/- 2.5-3 deg.)
While LED and LED systems is what I do for the last 13 years, I never attempted to work on something with such a narrow beam at this intensity.
First I would like to know if somebody has any experience with such optics.
Second, it will be interesting to hear opinions about the single vs. multiple sources to match this intensity.
There are plenty of COB (chip on board) arrays available providing more than enough lumens, however the optical designers hate to work with them as they are far from being the ideal "point source".
From the other point, working with multiple sources each with it's own optics is also considered by some non practical, they claim the total power from several light sources all pointed to the same direction will be much less than the same power emited from a single source !? Is this true?
The smallest emitter I managed to get is 11.5mm diameter with an output of 1330 lumen at 17W. Why is it so hard to design a narrow beam optics?
Any input will be highly appreciated.
RE: Help needed with a LED project
The practical issue, particularly for such narrow fields of view, is getting the different sources to overlap appropriately. Think of two point sources 2' apart... you can make them both focus well together at 200', but at 5' the same focal direction will not match up the beams at all. If the point sources are only an inch or so apart, this will be somewhat irrelevant over the field of view you're looking at matching.
So, creating the optics itself for such a small angle isn't a problem for s single point source. Doing it for multiple points says you have to watch out for beam separation.
What you can do, if you have the room, is provide separate optics for each point source that send the beam to a combiner optic... form the standpoint of an outside observer, you're now dealing with a single point source. this can actually be a single piece made from cast acrylic/glass if designed correctly, and you can carefully control the placement of each point source in relation to each other and the optic.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Help needed with a LED project
The best you can hope for is to have multiple sources converge onto a single area at a single distance from the optic.
TTFN
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RE: Help needed with a LED project
Pointing all to the desired distance, say 200m makes sense. This is of course a very small adjustment but interesting idea to explore.
There are two other dilemas speaking of the design:
What is preferable - reflector or TIR collimator?
I tested lots of reflectors plastic and metal small and large for different projects - all designed for LED by the way - the results are quite dissapointing both efficency and beam sharpness. The TIR method seems to work better with LED but sill having a 15% average loss.
A thing I am considering is testing a combination of RBG leds instead a common white - I always had the feeling that making the optics for a white led is different then the result with any other color type.
It is like collimating a fluorescent vs. filament. The way white leds are built considerably increases the light emitting surface, as the die is not the emitter, the entire phosphor substrate is. With a color LED the source is much smaller (the die itself).
Is this my feeling or there is an explanation?
RE: Help needed with a LED project
Sounds like you need to more carefully specify what you're willing to give up performance-wise for certain gains...
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Help needed with a LED project
I was just describing one of the dilemas I am facing.
About the projector, it is supposed to be a hand-held device as small as possible, preferable 4-5" diameter.
I can use any type of led commercial or custom made.
Having cooling limitations, the best will be to settle at 30-36W providing at the best 3000-3600lm and if absolutely necessary, can somehow get close (with some limitations) to 50W.
I measured an old projector with a 100W filament lamp, quite a large one, 7-8" diameter. It makes the 6 deg beam with 4 lux at 200 meters. The bulb was measured in an integrating sphere and the total flux measured was <2000lm.
It seems like the problem is finding an open mind optical designer. As described in my first post, so far those I meet are only raising the problems expected, none of them attempting to find a solution. It seems LED is scaring them.
RE: Help needed with a LED project
To point out another issue... I hope you plan on having a lot of forced cooling. 30-50W in a hand-held device is no simple matter, and LEDs cook quickly!
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Help needed with a LED project
So what would be the realistic expectations as you see them?
RE: Help needed with a LED project
Your 6x6 array has a maximum physical extent of ~27 mm. To get a 6° spread from this extended target requires a focal length of 257 mm. Assuming a 2-inch clear aperture, the optic would collect no more than 11° of the emitted 120° FWHM cone of light. That means that only about 1% of the emitted light will actually get projected through the optic.
TTFN
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RE: Help needed with a LED project
If the design was impossible nobody will be shy and will say this upfront. One thing I learned through the years is never make sugestions or show my way of thinking as the designer for some reason gets "locked" in this direction and will not try to think of other options. I do offer or explain all the possibilities available.
Now, the 36 led array (spread on a round aluminum pcb and not exactly 6x6) were mentioned to give macgyvers2000 an answer about the heat question.
They were used in another project, with TIR collimators in one case and tiny reflectors in another (both types available commercially)- and I mean one for each LED.
Speaking of that, the beam produced was 22deg with the reflectors and 18deg with the TIR - up to 50 meters it looks great.
There was no intention to try and collimate this led array.
By the way, Lamina Ceramics offers some large reflectors for their Titan 7 emitter module - one of them for 9 deg and another for 11 deg. I made some testing with both and it was dissapointing.
But the point is, they do exactly what you were talking about - a single reflector designed to concentrate light from 7 sources spread on a 1.25" (31mm) diameter PCB with a 6" (150mm) reflector.
check this link: http://p
RE: Help needed with a LED project
There are other LED couplers on the market and plenty of CPC's out there. The Luminus Devices LED might be a little expensive and a current hog for what you are doing but then you didn't say what the limits were in those regards.
Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600
www.lumenflow.com
RE: Help needed with a LED project
What a coincidence - I was just looking the other day at the CSM-360, just got the data sheet from a friend. It has a 16mm dome and impressive lumen output.