visibility of void / antimatter photon port surface in irradiance rendering

Hi Radzilla-users,

I made a strange observation that I want to share. Most probably it is my fault, but it would be great if someone could shed some light (or photons) onto this.

I define my photon port surfaces as such:

void antimatter photonPort
1 void

This should always be invisible. Right? At least I have no clue what could be seen here...

I call rzpict with -apem on -apo photonPort and so on...

Now I have put a box of photonPort-faces (five faces - to the side and to the top) around a sky-light. And - I can see this box as white in front of my blueish glow sky on an irradiance rendering of the section thru this system!

Well, I know that irradiance values can be wrong when calculated by rtrace or rzpict with the photon map. Still, the visibility of a non-defined surface makes me worried that something more fundamental may be wrong here.

Any comments?

CU Lars.

I attach a VERY small rendering of the section of the skylight, which is of such small file size that it should be acceptable. It still should give a better idea of what I describe.