Quote - question: how to grasp irradiance in poser.   answer: don't use irradiance cache (IC).  machine: ordinary imac from 2009, 2 hr. render.  was thinking of getting newer faster one to watch blu-rays, but old ones are fast enuff for poser, and new macs don't ship with blu-ray drives.  avoid smoothing these primitives when possible.

So without the interpolation (IC) enabled, Poser's IDL method is about the same as brute force Monte-Carlo GI methods in other render engines, except there are still render artifacts that can not be cleaned entirely.  Although the artifacts are minimal in your last render of the Cornell box, if one were to include additional geometry in a much more complex, but similar scene; with reflective or refractive materials, more sharp angles, and adjoining corners, the results would more than likely be troublesome, with render times not much better than something like Luxrender (depending on your hardware).  If we only had access to control the probabilistic subdivision sampling, we might be able to finness a virtually clean result from Firefly, but I don't think it's possible until additional parameters of the IDL sampling are unlocked/exposed to the user.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.