OKH hat eine Anleitung geschrieben wie man das macht.

Well, rather an appendix to the SVG mini guide. But with little detail, it does not describe how to add multiple light-sources one model. However, in the Forum there is good advice in several places - also how you can place lights manually in the SH3D plan. That said, for a neon light, my off the cuff advice to avoid too many complications, would be to use a model with a box and transparent lettering so you can place the lights behind the transparent parts in the box.

But much better, look to the rendering-experts, e.g. posts by enkonyito and Ceciliabr, such as the Chinese ghost city.