Radiometry from Blender rendering

I’m developing a Space scene in Blender, using a phisically accure lighting, and I would like to know if it is possible to obtain radiometric values from a rendered image, starting from the RGB values.

Not sure if this is what you mean but EXR files allow you to save HDR open domain scene linear information instead of just between 0 and 1. You can try EXR file format.