Costumer Angela Clayton, with whom you may already be familiar from when her Elsa the Snow Queen costume went viral, made a gorgeous “Christmas Angel” costume which featured a light-up skirt. You can see more photos of the costume here and read her build notes here and here. (While you’re there, be sure to check out the rest of her costumes, particularly the adorable Halloween-themed flower dress near the bottom of this page.)

Here’s a short video of the light-up effects:

Clothing with battery-powered lights has been around for ages–I fondly recall a 50’s-vintage skirt belonging to my aunt which featured a felt Christmas tree with working lights on the branches–but modern wiring, lights, and battery requirements are vastly improved and easy to use. Today, if you want to add dramatic lighting to the folds of your wizard’s cloak or wear an appliqued bat with glowing eyes, there are tons of supplies and resources which make it easy.

In addition to Clayton’s tutorial, there’s a good easy-to-follow tutorial at Gizmodo, and some some general tips at CreativeBug. If you’re feeling more ambitious, MIT professor Leah Buechley has some pretty awesome instructions for creating a tank top with a microcontroller that can be programmed to spell messages or run a Life session.

Wired has a good overview of materials for sewable circuitry, and you can buy supplies at SparkFun or Evil Mad Scientist.

A simple circuit with a couple of LEDs is an easy project that’ll give you confidence to try more elaborate effects. It’s also a good intro to the world of programmable circuitry; after you’re comfortable adding circuitry to clothing, you can move on to elaborate Jack-o’lantern light displays.