Collimating high power LEDs

Discussion in 'General Electronics Chat' started by pmd34, Mar 16, 2019.

  1. pmd34

    Thread Starter Active Member

    Feb 22, 2014
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    I feel very old when I look back and remember how you could only get red wimpy little LEDs "a few" years back ;).
    The high power LEDs you can get so cheaply now are really quite phenomenal (off the scale almost for the old laser class XX markings), but the thought always strikes, me; isn't there some simple efficient way to collimate the light from one or more such LEDs, so you can then focus it down, and use it like a laser?
    Lasers are a bit too perfect for cutting and welding etc, not very efficient, and all your really making use of is the parallel nature of the beam, the coherence, monochromaticity etc are really overkill. Indeed the monochromaticity really ruins the efficiency when "pumping" the laser with another light source.

    I keep thinking along the lines of a parabolic reflector, or a light guide, but they're both a bit messy and would have questionable efficiency.. so... any bright ideas folks?
     
  2. mvas

    Active Member

    Jun 19, 2017
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    Laser Diodes and LED's are two different devices.
    analogy - Focusing many power flashlights will not make them into a laser beam.

    Exactly what do you mean by "collimate" ?
    Focus to point or make coherent ?
     
    Last edited: Mar 16, 2019
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Take a long tube, say 10m long, and put the LED at one end and a pinhole at the other. You will get a very narrow beam - but not much light.
     
  4. BobTPH

    Senior Member

    Jun 5, 2013
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    The monochromatic and coherent nature of a laser is what allows a narrow beam to remain narrow. If you do not have this, the beam will spread.

    Bob
     
  5. pmd34

    Thread Starter Active Member

    Feb 22, 2014
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    Erm no, the coherence is a result of the (size) of resonant cavity the beam is made in during the stimulated emission process, and the monochromaticity is a result of the atomic / molecular excitation states that are used to generate stimulated emission. The paralell nature of the beam is a result of stimulated emission produced by photons traveling along the axis of the laser perpendicular to the 2 cavity mirrors which are preferentially "amplified".

    Any point source can be made into a paralell beam. Even a diffuse source can as Albert points out, just not very efficiently. Hence able to focus the "paralell" rays of the sun to a spot and set fire to things with it.
     
  6. BobTPH

    Senior Member

    Jun 5, 2013
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    Focusing it to a spot is a completely different thing. It is narrow only at that one spot. Only a laser can produce a spot that barely grows in size over a large distance.

    https://en.wikipedia.org/wiki/Laser

    Bob
     
  7. pmd34

    Thread Starter Active Member

    Feb 22, 2014
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    Well guess we'll have to disagree on that one Bob.
    https://brainly.in/question/235371
     
  8. oz93666

    Distinguished Member

    Sep 7, 2010
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    This just can't be done .... It all comes down to how close to a point source the emitter is ...

    [​IMG] This is the best there is .... 10W , but the light emitting surface is about 2x2 mm This means you can't focus to a point .... Also the spread of wavelengths causes more problems because different wavelengths refract differently by the lens ....

    The above chips are used in led touches , to get an idea of what is possible get a zoomable torch and focus the beam down aim it at a wall. At 3meters from the torch you can get the beam focused to a 200x200mm square . The image is square cos the emitting surface is square , you can actually see the wires on the surface in the image on the wall. It is very intense ... at 30 meters the projected light would be 2x2 meters,

    These torches are very cheap , you could buy 100 and bind them together the beam would be blinding at 100 meters

    The same is true for sunlight .... Because the sun is not a point source it can never be focused to a point , by either a lens or parabolic reflector. holding out a finger 1 meter from your eye you can block out the sun .... 1cm(finger) to 100cm this means if your lens is 100mm diameter the smallest focused point you can get is 1mm dia,... With a 10 meter dia. lens you can focus to no better than a 10cm diameter dot.
     
    Last edited: Mar 16, 2019
  9. BobTPH

    Senior Member

    Jun 5, 2013
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    Your link says nothing about columnated light. The examples are focused light, which I said can be done without lasers.

    Focused: The light converges on a point. Everywhere else it diverges.
    Columnated: The rays of light are parallel. This can also be achieved without a laser, but it will spread more than a laser.
    Monochromatic, Columnated and Coherent: The rays are not only parallel but in phase. Theoretically, coherent light will not spread at all. In reality, lasers are not perfectly monochromatic or coherent so they do spread somewhat.


    Bob
     
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  10. Externet

    AAC Fanatic!

    Nov 29, 2005
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    pmd34 : Is this about white light ?
     
  11. pmd34

    Thread Starter Active Member

    Feb 22, 2014
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    I'm not that fussy it could be for Red LEDs if you like.
     
  12. Externet

    AAC Fanatic!

    Nov 29, 2005
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  13. MisterBill2

    Distinguished Member

    Jan 23, 2018
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    Some LEDs are available with narrower beams that do not spread very much, but they are nothing like laser beams. I have been seeking LEDs with narrower beams to replace laser assemblies because it is a good way to avoid what some perceive as a laser hazard. Now it seems that I may be able to find them. But they are not similar to laser beams by any stretch, just intense enough at 5 inches for my purpose.
    My cheap laser assemblies give a beam perhaps an inch diameter at 200 feet, while an expensive laser package produced a beam spot about 200 feet diameter on the moon. So the difference is in the quality of the optics, in addition to the beam being coherent. The LED beam is about 2 inches in diameter at my 5 inch distance, not in the same ballgame.
     
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