Gordon,
I have not done any light splines, the problem was unable to add a night mesh to a spline. If you are using lights you want them to glow at night.
The rules have changed after build 3.5 so that you have to adjust the emissive layer of an object so that it glows at night, instead of relying on the Trainz in-built night mesh option for builds 3.5 or earlier. I have been unable to get the emissive option to work for my models in build 4.6, so have used build 3.5 for any models that require a night mesh. I was able to make splines glow using an emission setting in some of my old road markers back in build 2.0, but that does not seem to work now.
I recall Minitrix did some runway lighting assets (build 2.0), "approach30m lights" for example, but this is a fixed scenery model showing an array of light standards. Not sure if he did any splines.
Ian