Anything that enhances the model should be considered. No paper purist here. You could get tubes of Silver conductive glue to make the paper itself circuit boards, and have a fully intigrated model, the LED ends, or Fiber Lights, would terminate at the ends of these traces, but then again, a very thin wire would do the same thing and cost far less. Most people use a far to heavy gauge of wire. You could do most of the lighting with fiber optics, and have 3 or 4 bulbs in the whole model (for different colors).