Electroluminescent wire is normally referred to in shorthand as EL wire, works by capacitation. The wire is actually made up of two wires – a copper core, coated with phosphor; and a very fine copper wire, which is wrapped around the coated core. An alternating current is passed between the two wires, charging one and then discharging into the other (and vice versa) – which makes the whole wire turn into a coaxial capacitor with roughly 1 nf of capacitance for every foot of wire.
As a result, electroluminescent wire is very energy efficient, and requires only a couple of AA batteries to make it glow for hours on end. A few hundred feet of electroluminescent wire can be driven by AA batteries for a whole night, making the wire perfect for nightclub installations and theatrical productions.
Around the fine wire and copper core, there’s a clear protective sleeve. Around this sleeve is another sleeve, made of PVC coloured to react with the glow of the excited phosphor.
Normally, naked electroluminescent wire glows either bluish green or bluish white. So the colours of the final PVC sleeve are designed not to show as their own colour, but to combine with the colour given off by the excited phosphor to make a new colour. Typically electroluminescent wire is available in a range of oranges; reds; greens; blues; yellows; and pinks.
The current potential required to excite the phosphor is between 90 and 120 volts at roughly 1,000 HZ. In order to generate the drive signal required to get the electroluminescent wireglowing, hobbyists will commonly use a resonant oscillator and a coiled transformer. The combination of the capacitance load of the wire itself, plus the transformer, turns the oscillator into a tuned driver.
A tuned driver, which is also referred to as an L Oscillator (the L stands for “resonant” in electrical terminology), storing energy at the resonant frequency of the circuit. In effect, this makes the whole LC circuit act in the same way a tuning fork does – it stores energy resonating at its own frequency, thereby enabling a sustained delivery of super-efficient power over a long period of time. Think of this as analogous to when you strike a tuning fork. Even a small tap will give a pure note that lasts for some minutes before it dies away.
It is for this reason that electroluminescent wire is so effective in applications where light is required with little power. Also, this makes the wire a good choice for applications where light or detailing is required but no heat can be generated by the light source. Because of the tiny amount of power used to run the electroluminescent wire, the illumination it gives off is virtually heat-free. In the trade it is known as cool illumination, and is perfect for installation in devices where the heat of a bulb or lamp might present problems for surrounding components or case materials.
Working as an almost pure circuit with virtually no resistance, electroluminescent wire is ideal for a number of applications.
Ben Nielsen is a physics lecturer at the University of Bradford. In his spare time he tinkers with electronics projects involving electroluminescent wire.