Irradiance from this infrared light source after a diffuser

[Maker21538]

I need to calculate irradiance in a system shown on the image.
There is an infrared LED on the left and a diffuser in front of it. I need to calculate irradiance at a certain distance after the diffuser.

I think I first have to calculate irradiance at the diffuser. Then multiply it by the transmission of the diffuser to know how much radiation gets through the diffuser. That's where I don't know how to proceed. I don't know how to take into account the effect of radiation output angle from the diffuser.

 

[hutchphd]

I need to calculate irradiance in a system shown on the image.
There is an infrared LED on the left and a diffuser in front of it. I need to calculate irradiance at a certain distance after the diffuser.

I think I first have to calculate irradiance at the diffuser. Then multiply it by the transmission of the diffuser to know how much radiation gets through the diffuser. That's where I don't know how to proceed. I don't know how to take into account the effect of radiation output angle from the diffuser.
View attachment 241502

You need to characterize the output of the diffuser to a "pencil" of light (experiment? info from supplier?) and convolve it with the emission pattern of the LED. Ray tracing programs will do the arithmetic but you need to know the patterns.

 

[Maker21538]

You need to characterize the output of the diffuser to a "pencil" of light (experiment? info from supplier?) and convolve it with the emission pattern of the LED. Ray tracing programs will do the arithmetic but you need to know the patterns.

I have the datasheets for both the LED and the diffuser so all the info needed should be available.
Are there any good and free ray tracing software out there? All I can find is a few software for lens design.
Could the calculation be done as a stochastic simulation in some mathematics software?

 

[Andy Resnick]

I have the datasheets for both the LED and the diffuser so all the info needed should be available.
Are there any good and free ray tracing software out there? All I can find is a few software for lens design.
Could the calculation be done as a stochastic simulation in some mathematics software?

Ray tracing is a bad approach for this problem, since diffusers are not well-characterized in terms of a transfer matrix. I agree with hutchphd, the easiest path is probably to simply convolve the LED output irradiance with the diffuser profile. As far as commercial programs, both FRED and ASAP can handle nonimaging design problems.

 

[hutchphd]

Are there any good and free ray tracing software out there?

It has been a few years but Image J from NIH used to be good and free. This is image processing software and you can do all kinds of good stuff, including convolutions and FFT of images. Lots of add-ons around.

 

[Maker21538]

This is a hobby for me, so any kind of commercial software is out of question.
I have a background in mechanical engineering and only know the basic photometric and radiometric principles. Therefore there is much I don’t understand.

To use the ImageJ I should have grayscale images representing the emission patterns of the LED and diffuser and then colvolve them? Am I correct?

 

[hutchphd]

Yes. You should definitely get to know imageJ then. The software is written with medical/biological applications (diagnostic images, fluorescence) in mind so there is a lot of good but not overpoweringly technical literature available. As I recall there is a built- in function that allows you to define an arbitrary "filter" some pixels in size and apply it (convolve) to any other image. Have fun.