Edit to the question: I found how that the problem was due to the default smoothing, which was set to 8. By changing it to None I “almost” solved my problem. However there is a little problem.  When I generate a single ray, I would just the hit pixel to light. However it often happens thay 2 or 4 pixels light together in the 40 x 40 configuration (for “light” I mean that an inchoerent irradiance different from 0 is observed). I also forgot to specify that in my application I’m using the simple ray splitting option (I would need to treat the ray as much “single-photon-like” as possible). Is there a way to visualize only the “actually” hit pixels? (For examples by changing options for some kind of generated noise)

Hi Nicola,

In the Object Properties for the Detector Rectangle there is a check box labeled ‘Use Pixel Interpolation’. When this is checked, the power of a ray striking a pixel is interpolated to neighboring pixels depending on where it hits the pixel. If you uncheck that, then the power will only be assigned to the pixel the ray hits. The interpolation is useful when using the detector reading for optimization.

It works, thanks a lot,