3. Light Layer
Turn off eye icon on black line layer.
Turn visibility on green line layer and start selecting all green areas inside the drawing. Use magic wand tool with tolerance of 50 (status bar).
Once you´ve selected all green areas with the Magic Wand + Shift (for multiple select) go to menu>Selection >Expand. Depending on how bright or dark your final lines ended up in THIS layer you´d be able to set the value of 0.5 or 1 pixels, so that the current selection grows expanding itself 2 pixel more around the lines.
Now that all green areas in the green layer are already selected we go ahead and fill it with white. Shotcut: Press ALT+DEL to fill with foreground color (make sure it´s WHITE!)
Now Click CTRL+SHIFT+I (inverse selection) Press CTRL+ALT+D (feather) and put 1 or 2 pixels as value. Then Hit DEL. You are now happy with your light layer :)