Electroluminescent wire (often abbreviated to EL wire) is a thin copper wire coated in phosphor, which glows when an alternating current is applied to it. It can be used in a wide variety of applications- vehicle and/or structure decoration, safety and emergency lighting, toys, clothing etc - much as rope light or Christmas lights are often used. Unlike these types of strand lights, EL wire is not a series of points but produces a 360 degree unbroken line of visible light. Its thin diameter makes it flexible and ideal for use in a variety of applications such as clothing or costumes.
EL wire's construction consists of five major components. First is a solid-copper wire core. This core is coated with phosphor. A very fine wire is spiral-wound around the phosphor-coated copper core. This fine wire is electrically isolated from the copper core. Surrounding this 'sandwich' of copper core, phosphor, and fine copper wire is a clear PVC sleeve. Finally, surrounding this thin, clear PVC sleeve is another clear, colored translucent, or fluorescent PVC sleeve.
An electric potential of approximately 90 - 120 volts at about 1000 Hz is applied between the copper core wire and the fine wire that surrounds the phosphor coated copper core. The wire can be modelled as a coaxial capacitor with about 1 nF of capacitance per foot, and the rapid charging and discharging of this capacitor excites the phosphor to emit light. The colors of light that can be produced efficiently by phosphors are limited, so many types of wire use an additional fluorescent organic dye in the clear PVC sleeve to produce the final result. These organic dyes produce colors like red and purple when excited by the blue-green light of the core.
Thanks to Wikipedia and Electronics Warehouse for information.
(Picture credit: http://en.wikipedia.org/wiki/EL_wire