Shine-y
At Farthing Party, elisem mentioned a Cool Thing which I hadn't heard about: electroluminescent wire. It doesn't use much power and comes in a variety of colours; the potential applications for costuming are diverse. A child's costume could be spectacular, and driven by a couple of standard batteries. It doesn't have the same lifetime as electroluminescent night lights (which I've been using and appreciating) but it's plenty long enough for costuming purposes; it is also, alas, not cheap. Still... hmmm.
(The materials-science geek in me suspects that the limited lifetime may be due to degradation of fluorescent materials used to convert from the usual green-blue / "aqua" / cyan electroluminescent phosphors to other colours, and that if one were willing to settle for the natural emission colour, the wire would last much longer. There may be other breakdown factors that haven't occurred to me.)
(The materials-science geek in me suspects that the limited lifetime may be due to degradation of fluorescent materials used to convert from the usual green-blue / "aqua" / cyan electroluminescent phosphors to other colours, and that if one were willing to settle for the natural emission colour, the wire would last much longer. There may be other breakdown factors that haven't occurred to me.)