Here's a look at the finished diorama, with some notes about how the painting and final assembly came together:
The lamp and Gutter Runner were painted separately from the base. The tunnel with its pipe and cables was first painted in "normal" colors– Grey stone, rust on all the metal, etc.
Once it was painted, I sprayed Tamiya Camel Yellow at an angle from the end where the lamp would be. This was the make-or-break moment because it could have easily been a disaster. Fortunately, I had a little leeway, because the yellow isn't very opaque.
The yellow created a lighter tone on the highlighted areas, and over this I applied some drybrushing and glazing with a mix of P3 Iosian Green and GW Yriel Yellow. The lamp was painted to match the colors of the glow, and then glued in place.
The figure was also painted to match the rest of my Skaven Army...
...and then sprayed and glazed in the same manner as the tunnel.
After the model was pinned in place, I cut a small rectangle of craft foam for the bottom of the diorama.
And here's the final piece! I painted a little bit of a shadow under the Gutter Runner and the pipe. Overall, I'm pretty happy with how the source lighting turned out, and had a lot of fun with this little project.