From Bad Ass Helmet Store

"What exactly is the EL wire?

LightMode Electroluminescent Motorcycle Helmets on female ridersEL wire also known as Electroluminescent wire. It is probably one of the simplest solution for adding light within a project. EL wire is a very thin copper texture that is flexible and gives off a very bright glow along the whole length of the article. When looking at it, it is not unlike a chemical glow stick. It is also waterproof, very cool, can be sliced to any size or length that you may want, and as long as each one of the joints are properly isolated, it will not wind up shocking your body through the electricity that goes through it. Each one of those (along with its more than passing resemblance to the piping on one of the Tron outfits) make it a very popular choice for light up costumes, clothing, and many other accessories. Since it is very energy efficient, EL wire is also used for lighting indoors, and in different types of vehicles.

EL wire does require an alternating current source, which means that you will need to connect to a transformer. Usually a small battery powered box that can be tucked away somewhere on your project, or inside your costume, making it harder to be noticed. Greater lengths of EL wire will require you to use more power."

http://badasshelmetstore.com/helmet-lights-light-helmet-like-tron/