Attached Link: http://www.renderosity.com/messages.ez?ForumID=10139&Form.ShowMessage=1318136

If light set A contains Light1, Light2, Light3, and light set B also contains Light1, Light2, Light3, then applyig light set B will just overwrite light set A. If light set A contains Light1, Light2, Light3, and light set C contains Light4, Light5, Light6, then applying light set C will add Light4, Light5, Light6, and turn off Light1, Light2, Light3. At least thats my understanding of how it works. You can add lights to a scene via a pp2 or cr2 file, doing it this way will not turn off lights that pre-exist in the scene, but any light you load that has the same internal name as a light in the scene will always overwrite that light. Say you wanted 2 light sets, one with 6 infinate lights, and one with 6 spotlights, and you wanted to be able to load both sets with out turning one of the sets off. It could be done by creating 1 lt2 file with 12 lights, then hacking it in two and putting each half in a diffrent pp2 file, but you would have to be fairly familiar with editing Poser files. The naming and numbering system Poser 4 uses for lights and their associated SHADOW_CAM_LITE's can be very confusing untill you have had a bit of practice. If you do feel you want to have a go at this there is a bit of info on loading lights from pp2 and cr2, in the thread linked above. I don't have time to explain the entire process, but if you hv any specific questions I'll try to answer them. But perhaps you should save yourself a headache and just make one big light set with infinate and spotlights.