I have an application with LEDs with following data sheet

  • LED631E 635 nm
  • optical power 4 mW
  • half angle 20°
  • FWHMa 10 nm,

Could you help me with calculation of beam area at the distance of 20 mm from LED?

Also please help me with calculation of dosage (J/cm2) and total energy delivered [Joules] in 20 minutes at the same distance : 20 mm from LED.

Thank you a lot.


Assuming that you only care about the energy within the half angle (angle at which the magnitude is 50%), here is what I come up with. Without a curve of brightness vs angle the amount within the half angle can't be determined. I made a wild guess. With the curve, you will need to integrate in polar coordinates, something I might have been able to do 40 years ago, no chance now without many hours of research.

I am guessing that you will need multiple IR LEDs for your application, to calculate the optical power with overlapping curves will probably be necessary.

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  • \$\begingroup\$ Thank you for your answer. Yes it is about 10 LEDs placed in line . I have another manufacturer with the same type of LED and the characteristics are in the link below : thorlabs.com/drawings/… \$\endgroup\$ – Costas Apr 7 '19 at 23:16
  • \$\begingroup\$ Yes. You are right, i have an application with 10 LED s with red colour 635nm for obtaining an uniform lighting of a rectangle surface of 30mm x 100 mm. The distance 15 or 20 mm is for finding of calculation formulas. I need red for special application of Photoactivation device used for activate with red, green and yellow., link for what I want to do : manualzz.com/doc/7171031/adilight-2-user-manual \$\endgroup\$ – Costas Apr 7 '19 at 23:53
  • \$\begingroup\$ I want to build for me an Photoactivation device, that produces red, green and yellow colour for photoactivation of stem cell and PRP. The patent for above model is in the link : patentimages.storage.googleapis.com/c2/5b/0b/ea71b328591a4a/… \$\endgroup\$ – Costas Apr 8 '19 at 0:20
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    \$\begingroup\$ You may want to specify the tolerance on radiated Max:Min which is necessary but impossible with the LED specs given as the overlap will create a wide variation in dosage. unless you use a diffuser. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 8 '19 at 0:23
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    \$\begingroup\$ for LED illumination you need a better design for smooth intensity and not just 5mm LEDs every 25mm \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 8 '19 at 0:42

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