Collimating incoherent light emitted by a LED

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Discussion Overview

The discussion revolves around methods for collimating light emitted by a LED with a specific emitting area and divergence angle. Participants explore various optical configurations and techniques to achieve a smaller beam diameter while minimizing light loss.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the best method to collimate LED light into a beam of 5-10mm while minimizing light intensity loss, mentioning the use of an aspheric condenser lens.
  • Another participant suggests that maintaining a significant fraction of light in the beam is challenging without adding lenses every few centimeters, indicating a limitation in reducing the phase-space size of the light.
  • A third participant agrees with the previous point, noting that the large size of the LED emitter restricts the ability to collimate the beam effectively without significant loss.
  • The original poster clarifies that there are no distance limitations for the beam and seeks methods to reduce light loss, mentioning a previous setup that resulted in significant loss when using a pinhole.
  • One participant humorously suggests using a laser LED, which comes pre-collimated, as an alternative solution.
  • The original poster expresses a preference to continue using a standard LED instead of switching to a laser LED.
  • Another participant describes a standard method of producing a parallel beam using a lens to create a reduced image of the light source onto a pinhole, followed by another lens for collimation, while acknowledging the light loss involved.
  • A later reply comments on the implications of distance and power from incoherent sources, contrasting them with laser diodes, which are also subject to diffraction limits.

Areas of Agreement / Disagreement

Participants generally agree on the challenges associated with collimating light from a large LED emitter and the resulting light loss. However, there are competing views on the best methods to achieve collimation and the feasibility of using alternative light sources.

Contextual Notes

Participants mention various limitations, including the phase-space size of the light and the inherent losses associated with using pinholes and lenses. The discussion does not resolve these limitations or provide definitive solutions.

jcfutbal
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Hello,

What would be the best method to "collimate" light from a LED with an emitting area of 12mm^2 and a maximum divergence angle of 80° with minimal loss of light intensity?

I want to collimate it into a beam of approximately 5-10mm.

I have an aspheric condenser lense at hand with an effective focal length of 13.7mm. This lens succeeds in making the beam spherical, with a diameter of approximately 30mm at the focal length, but it still undergoes significant divergence. I have tried adding more positive lenses into the optical system to try, but I can't seem to create such a small beam diameter without losing a great portion of the emitted lighted.

Is there any particular lense configuration I could use?

Thanks.
 
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I think it is hard to keep a significant fraction of light in the beam, unless you add a lense every 2-5 cm or something similar. You cannot reduce the phase-space size of your light, no matter how the setup looks like.
 
Last edited:
I agree with mfb- the large size of the emitter restricts your ability to collimate the beam at even a moderate diameter without lossy beam shaping (spatial filtering, for example).

Over what range does the beam need to be 5-10mm in diameter?
 
there is no limit as to distance, as I have a lot of mirrors available and a lot of workspace. what is the best way to reduce the amount of light lost? I managed to "collimate" it to a diameter of about 10mm, but in order to do so I used a setup similar to a pinhole and I lost a lot of light. but to me at this stage a pinhole seems the way to go...
 
to ask the obvious...

why not just use a laser LED ?? already collimated with built in lens :)

Dave
 
i want to try and use a LED instead!
 
You´re perfectly right about the pinhole.
The standard way of producing a parallel beam used to be:
Use a lens to produce a (reduced) image of your light source onto/into a pinhole. Try to capture as much of the light as possible.
On the other side of the pinhole, use a lens to produce your collimated beam. Then you use autocollimation to adjust the position (and tilt) of the lens for minimal divergence (and beam position). Beam size adjustment requires a diaphragm.
But of course you will lose a lot of light this way. You can vary the pinhole size for the best compromise.
And you´d better use an optical bench or an optical table for mechanical stability.
 
"no limit as to distance" implies zero power from an incoherent source, even if there were no diffraction.

A laser diode would be limited by diffraction. You get one diode in each CD or DVD reader-burner.
 

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