Thank you for the tips, microwar. Image wrapping is still a bit of a problem for me, but I'm getting the hang of it.
I think I should clarify the origins and purpose of the project a bit, though. I wasn't setting out to recreate the Earth at night, per se. What I wanted to do was be able to "realistically" place cities on a generated planet (example of what I'm trying to accomplish in the two pics attached - before and after). Although I could put a light source, plug in values until it looked good and then call it a day, that's just not how I roll. So I took data from some government reports which calculated energy consumption in the U.S., and applied that data to U.S. cities; then I took the outcome and made approximations to light sources in Terragen.
Since I was using U.S. data as the basis for the project, I created the map of the U.S. at night just as a proof of concept piece, i.e., I wanted to be sure that the formula I came up with worked in a realistic manner. For the most part, it has; so I've decided to continue the project beyond a mere test and into something full blown, and I thought it'd be a neat thing to share.
The other value that this project has for me is that it serves as a kind of study for migration patterns: How cities group together around each other and terrain (e.g., densely populated coasts and river basins versus open plains, deserts, and mountain ranges). That should also help when I set about populating the final product.
Tips-wise, I think it would be helpful to learn how I can make the cities appear less spherical, since the light source is omnidirectional.
Thanks again for the feedback.