Okay, I'm having a hard time rendering the mountain heights on the gray texture layer because the following path does not seem to exist in my copy of Gimp
"Filter -> Render -> Lighting Effects"
I DO have "Filter -> Light and Shadow -> Lighting Effects"
but once I open that filter, of the following settings, only Light Type and Intensity exist, along with a whole bunch of other variables. Is your Lighting Effects a custom plug-in or is it an issue with differing versions of Gimp? I'm using 2.68
Light Type: Directional
Gloss: -15 (0 is fine too)