Creating a ground light with PaintShopPro7...

Hi all,I seem to be having great difficulty creating a light with an alpha channel and using DXT3 for a transparency. I know how to make masks etc and do it for all kinds of other ground objects. How would I go about placing a light on an invisible background, so that only my light will appear? I cannot get a light to display on a pure black background a all. It will appear on any other color but ofcourse that bleeds through the mask when rendered in FS.I hope I've explained this in an understandable way.Thanks,Adam