Mario, I don't know the answer to your question, but I would suggest going over to RDNA's Poser 6&7 forum and asking Olivier.  There are a number of people who are very good with lights, but Olivier is the guru IMHO.

http://www.runtimedna.com/mod/forum/messages.php?forum_id=95

I put together a thread of bookmarks especially for lighting. There are some links in there that might help you.

http://market.renderosity.com/mod/forumpro/showthread.php?thread_id=2662390

Here are a few links from there that are a must read for Poser lighting:

Olivier's Making of a pomo pic
Castle Poser Tutorials
Poser 6 IBL Ins and outs by Olivier
A little tutorial about lighting by Olivier
Tutorial: GEL MAPS by Olivier
How Light Probes are Laid Out
Advanced Image Based Lighting in Poser 6
Basic OpenGL Lighting

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi