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Electroluminescent wire (often abbreviated to EL wire) is a thin copper wire coated in a 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, coated with phosphor. A very fine wire or pair of wires is spiral-wound around the phosphor-coated copper core and then the outer ITO conductive coating is evaporated on. 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 alternating current electric potential of approximately 90 to 120 volts at about 1000 Hz is applied between the copper core wire and the fine wire that surrounds the copper core. The wire can be modeled 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.
A resonant oscillator is typically used to generate the high voltage drive signal. Because of the capacitance load of the EL wire, using an inductive (coiled) transformer makes the driver a tuned LC oscillator, and therefore very efficient. The efficiency of EL wire is very high, and thus a few hundred feet of EL wire can be driven by AA batteries for several hours.
In recent years, the LC circuit has been replaced for some applications with a single chip switched capacitor inverter IC such as the Supertex HV850, this can run 1 foot of angel hair wire at high efficiency suitable for solar lanterns and other safety applications. The other advantage of these chips is that the control signals can be derived from a microcontroller so brightness and colour can vary depending on battery state or ambient temperature.
EL wire in common with other types of EL device does have limitations, at high frequency it dissipates a lot of heat and that can lead to breakdown and loss of brightness over time. There is also a voltage limit, the typical wire breaks down at around 180V p-p so if using an unregulated transformer back to back zeners and series current limiting resistor is essential.
A recent innovation is "quantum EL" or FIPEL, this uses a very small amount of carbon nanotubes around 0.04% wt and an iridium based PPV organic compound to increase the efficiency of the resultant lamp to nearly 8 times that of a conventional lamp with a consequent reduction in heat production. These lamps can rival OLED with the advantage that they do not degrade as quickly with heat or light so can be used outdoors with a suitable moisture barrier film. In addition EL sheet and wire can sometimes be used as a touch sensor as compressing the capacitor will change its value, 
See also 
|Wikimedia Commons has media related to: Electroluminescent wire|
- How Electroluminescent (EL) Wire Works, by Joanna Burgess // How Stuff Works