I am trying to build a LED flashlight with a large throw (beam of light should reach very far, be as parallel as possible). I am using a led with approx 84watt (10x10 COB, 100Watt rated) which should produce approximately 8000 Lumens.

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I am struggling in terms of lens/reflector choice:

Currently I am using:

The produced beam is currently approximately 30 degrees.

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The approximate dimensions/shape of the reflector can be seen in the drawing below, they are not perfectly accurate since i measured with a measuring tape

The lens/reflector setup is pictured below: enter image description here

What can I do to tighten the beam apart from buying a smaller size LED so that the light source is more similar to a perfect (point) light source**?** Thank you very much for your help! Any input is greatly appreciated :)


1 Answer 1


Using a lens/mirror with a longer focal length will make the beam tighter, but it will reduce the brightness if you do not also increase the size of the aperture in proportion to the increased focal length*.

Fresnel lenses can be made with a very good ratio of aperture to focal length, and they often are used to collimate light into tight beams when maximum brightness is required.

Using a smaller light source will make the beam tighter. But, you'll have more of a challenge managing the heat produced by a tiny light source, as compared to removing heat from a larger source that puts out the same total amount of light.

If you really want the tightest possible beam, there's just no substitute for a laser.

* The ratio of focal-length divided by aperture (assuming a circular lens) is known to photographers as the "f number." Smaller f numbers mean larger aperture and more light.

  • $\begingroup$ Thank you very much! could you please elaborate on how using a larger Focal Length will tighten the beam? My theory (but i could be totally wrong) is that because the lens will be further away from the led chip it (the led chip) will more closely resemble a point light source which will result in a tighter beam. Please correct me if i'm wrong. $\endgroup$ Commented Nov 11, 2019 at 15:24

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