How to calculate Relative Illuminance through integration

  • 14 September 2021
  • 2 replies

In Help Files of ZEMAX, It tells me that the relative illuminance is calculated by integrating the effective area of the exit pupil observed from the image point. The integration is performed in cosine space, using a uniform grid of image-square cosine space.
I would like to know whether it is possible to reproduce the calculation of RI by ZEMAX through ray tracing and programming or other methods? Please feel free to enlighten me.

Thank  you all



Best answer by Angel Morales 16 September 2021, 23:49

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Thanks for your post here!

I think a good source of information for you would be to check out the forum post FAQ about Relative Illumination | Zemax Community. Our Principal Optical Engineer, Michael Cheng, has some great details about how OpticStudio generates relative illumination results based on the paper “Relative illumination calculations” by M. Rimmer. One approach would be to generate a grid of rays that enter your optical system, and once they are in the image space of your lens, you’d also need to ensure that they are uniformly distributed in direction cosine space. There is some discussion on that forum post and in the paper about some techniques to achieve this.

What you also might find useful is a method of computing relative illumination by reversing your system so that physical image plane is defined as the Object surface. With that reversed system, you could send rays from a perfect point on your “Object” surface and obtain relative illumination results in that way. We have a forum post that documents this method and provides some sample code as well: How to check relative illumination at 'object' surface (verify the relative illumination theory) | Zemax Community

Thanks again, and let us know if you have any more questions!

Hi Angel Morales

   Thank you for your reply!your explanation and link given are very useful to me. But they are a bit complicated, and I still need some time to understand them. Thank you again!