Vince ( you're french?), the luminosity parameter I mention is in the advanced material editor, not in the function editor,  light and effects tab ( My Infinite is in english, though I'm french, so I don't know how it is translated), in front of he word luminosity, there is a lightning icon ( icone "éclair), click on this icon, then you get to the function editor, and there you can  drive the luminosity parameter by a bitmap, the luminosity map you created in a paint program. But maybe the parameter cannot be driven by  a function in Esprit. This, I don't know.