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\begin{document}
\onehalfspacing
\technote{6}{Dan Ports}{2004/04/09}{drkp@mit.edu}
\tntitle{Electroluminescent Wire}


\section{Electroluminescent wire: the technology}
\label{sec:el-wire}
Electroluminescent wire (\emph{EL wire}) is a relatively new
technology that is not widely used in the theater. However, it is a
versatile material that can be used for many lighting effects. This
note describes the technology and its advantages, explains the process
of wiring EL wire, and documents (with many pictures!) a lighting
installation using EL wire.

Electroluminescent wire is, quite simply, a cable\footnote{Not a wire,
  oddly enough --- it's actually a cable with at least two wires.} that
glows. The glowing is accomplished by an electroluminescent phosphor
that emits light when a voltage is applied across it. EL wire, then,
consists of an inner wire with the phosphor coating applied to it, and
an outer wire wrapped around it. This pair of wires is encapsulated in
a protective plastic coating. (Figure~\ref{fig:livewire-diagram})

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-livewire-diagram}
  \figcaption{EL wire diagram (Source: LiveWire Enterprises, Flushing, NY)}
  \label{fig:livewire-diagram}
\end{figure}

To make the EL wire glow, an AC voltage is applied between the inner
and outer wires. Typically, a voltage of between 100 and 200 AC volts
RMS is used, at a frequency in the low kilohertz. Conceivably, it
could simply be wired directly to the standard 120 VAC, 60 Hz line
power, but the brightness of the emitted light depends on the
frequency of the power, so the wire will not glow brightly. Instead,
an inverter converts DC power to a high-frequency AC output. These
inverters simply take a two-wire DC input, and generate a two-wire AC
output; they are inexpensive (about \$10 \cite{coolight},
\cite{elwirecheap}) and small enough that they can be concealed
wherever necessary --- including in a costume. The DC input power is
typically 6 to 12 volts DC, and can come from either a battery or a
common ``wall-wart'' DC power supply. Note that the AC voltage is
applied between the inner and outer wires of the cable, not between
the two ends of the wire --- the power connection only needs to be
applied at one end of the cable.

The wire is available in a variety of thicknesses, from 1.2 mm to 5
mm. The smallest thicknesses are quite thin indeed, perhaps too thin
to be very useful at theatrical distances except in certain special
cases. Many colors are available; the phosphor emits a specific color,
and the plastic outer coating is colored to further filter the output
color.

\section{Advantages and disadvantages}
\label{sec:advantages-and-disadvantages}

EL wire has a number of advantages that make it potentially useful for
a number of applications:

\begin{itemize}
\item It is very flexible and can be easily shaped into the desired
  design.
\item It is thin enough to install just about anywhere.
\item It does not need much power, and the required inverter is
  very small.
\item It can be powered by batteries, eliminating the need for a 
\item It is safe and does not run hot.
\item It can stand up to some amount of abuse (the thicker versions
  can also be used outdoors, though that may not be too helpful in the
  theater)
\end{itemize}

Its principal disadvantage, however, is that its light output is
limited. Certainly it cannot be used as a replacement for stage
lighting; in fact, one needs to be careful that the stage lights do
not overpower the EL wire. Careful planning with the lighting designer
is necessary.

Cost is also a concern.  Depending on the thickness of the wire, the
price can range from about \$1.50 to \$2.50 per foot. Long runs can be
expensive (though discounts for large lengths are usually available).

In the theater, EL wire is suited for a number of special lighting
effects. It can be used for decorating scenery --- it is ideal for
simulating neon signs (in fact, EL wire is sometimes referred to as
``flexible neon''). Since the wire is so flexible and can be powered
by a 9-volt battery and a small inverter, it can be hidden inside
props or costumes  \footnote{\texttt{\url{http://www.coolight.com/}}
  has some examples of pieces of clothing with EL wire built in. They
  happen to be truly hideous, but I'm pretty sure that someone with a
  decent sense of taste could come up with some much better ways to
  use it.}  that need to glow.

\section{Assembling an EL wire installation}
\label{sec:assembling}

This section illustrates the process of setting up an EL wire
installation using an installation I recently put together. This
installation had some nominal purpose, but mostly it was just a
specious justification to bask in the intrinsic coolness of a wire
that glows.\footnote{Some would say the same is true of this tech
  note, too. No comment.}

The materials for this installation are listed in
Table~\ref{tab:materials}. It features 30 feet of wire in two colors,
driven by a battery-powered inverter. The EL wire and inverter were
purchased from \cite{coolight}; other materials were already on hand
in my random-parts drawer.

\begin{table}[htbp]
  \centering
  \begin{tabular}{|r|l|}
    \hline
    \textbf{Material} & \textbf{Price} \\
    \hline
    EL wire, double-core, 20 ft, green & \$46.00 \\
    EL wire, double-core, 10 ft, ultramarine & \$23.00 \\
    Inverter, 9VDC to 150VAC, 2KHz & \$9.50 \\
    9V battery connector & --- \\
    Project box & --- \\
    9V battery & --- \\
    Wire, solder, glue, tape & --- \\
    \hline
    \textbf{Total} & \textbf{\$78.50} \\
    \hline
  \end{tabular}
  \caption{Materials}
  \label{tab:materials}
\end{table}

I used two colors of EL wire. The two strands of wire were connected
together to form a $30'$ wire. The inverter and battery were
attached at one end of the long wire. A small project box enclosed the
inverter and the connections, eliminating the exposed wiring, making
it safer, more durable, and more aesthetically pleasing.

Installing the wire was a fairly straightforward process --- except
that some parts of the wire wound up being harder to work with than I
expected.

The first step was to remove the plastic insulation around the
wires. This was difficult to do without damaging the wires inside,
especially the small outer wire. The most effective way I found seemed
to be to (carefully) use a wire stripper to start cutting the
insulation, then (even more carefully) finish removing it with a
knife. I then scraped the phosphor coating off the inner wires,
exposing the inner conductor (as in Figure~\ref{fig:stripping}).

\begin{figure}[p]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-stripping}
  \figcaption{Stripping the outer insulation (and doing unsafe things
  with knives)}
  \label{fig:stripping}
\end{figure}

Once the insulation is removed, the wires become visible. This
particular wire happens to be a double-core version, so it has two
inner wires. This means that twice as much current flows through the
two wires, each of which has its own phosphor coating, so twice as
much light is produced. We now discover the treachery of that
innocuous-looking diagram, previously seen in
Figure~\ref{fig:livewire-diagram}:

  \begin{figure}[h]
    \centering
    \includegraphics[width=5.5in]{21m735-tn6-wires-actual}
    \figcaption{EL wire, outer insulation removed}
    \label{fig:wires-actual}
  \end{figure}

As seen in Figure~\ref{fig:wires-actual}, the outer wires are revealed
to be tiny and nearly impossible to work with. They can't be any
larger than 30 gauge, and are quite possibly even smaller. My solution
to this problem was to attach two short leads of 22-gauge solid-core
wire to make the connection easier to work with. One lead was soldered
to the outer wires, and one to both of the two inner wires
(Figure~\ref{fig:soldering-leads}). This connection was then sealed
with hot glue (Figure~\ref{fig:glued-leads}), which served both to
insulate the connections and helped hold them together. Even so,
however, breakage of the tiny outer wires was still a problem.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-soldering-leads}
  \figcaption{Soldering the leads to the inner and outer wires}
  \label{fig:soldering-leads}
\end{figure}

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-glued-leads}
  \figcaption{Leads soldered and glued to the inner and outer wires}
  \label{fig:glued-leads}
\end{figure}

Next, an enclosure for the inverter and wiring was prepared. This was
simply a $1'' \times 2'' \times 4''$ project box. Two small holes were
drilled in one side for the battery connection, and one larger hole
was drilled on the other side (Figure~\ref{fig:drilling-box}) to pass
the EL wire through.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-drilling-box}
  \figcaption{Drilling a hole in the enclosure}
  \label{fig:drilling-box}
\end{figure}

The EL wire was then threaded through the large hole in the
enclosure. It was necessary to do this before joining the two lengths
of EL wire.

The next step was to connect the two pieces of EL wire. This required
stripping the two wires, and soldering their pairs of inner and outer
wires together, respectively (Figure~\ref{fig:soldered-join}). The
connection was then sealed with hot glue to insulate the two wires and
physically hold the connection together (Figure~\ref{fig:glued-join}).

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-soldered-join}
  \figcaption{EL wire connection --- soldered}
  \label{fig:soldered-join}
\end{figure}

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-glued-join}
  \figcaption{EL wire connection --- glued}
  \label{fig:glued-join}
\end{figure}

The far end of the second wire was taped over with electrical tape in
order to prevent any hapless observer from touching it and being
shocked.\footnote{This didn't stop one of my co-conspirators from
  zapping himself --- but that was his own fault.}

The leads on the first wire were soldered to the output leads of the
inverter (Figure~\ref{fig:inverter-connection}). Since the inverter's
output is an AC signal, the polarity of the leads does not matter.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-inverter-connections}
  \figcaption{Connection to the inverter}
  \label{fig:inverter-connection}
\end{figure}

The inverter and connections were installed into the enclosure, with
the inverter's input leads threaded through the small holes
(Figure~\ref{fig:inverter-in-box}). The enclosure was then closed.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-inverter-in-box}
  \figcaption{The inverter in place inside the enclosure}
  \label{fig:inverter-in-box}
\end{figure}

A 9V battery connection was attached outside the enclosure. The
battery was installed outside the enclosure so that it could be more
easily changed. This also allowed for the connection to be replaced
with an AC adapter if necessary. The inverter could be powered with a
battery for simplicity and portability, or from a wall adapter for a
more permanent installation. The result is in Figure~\ref{fig:final-setup}.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-final-setup}
  \figcaption{The final setup}
  \label{fig:final-setup}
\end{figure}

\begin{figure}[htbp]
  \centering
  \includegraphics[width=5.5in]{21m735-tn6-it-glows}
  \figcaption{It glows!}
  \label{fig:it-glows}
\end{figure}


\section{Finishing the installation}
\label{sec:finishing}

With the EL wire and inverter setup prepared, all that remained was to
shape and install the wire. Since the EL wire was so flexible, it was
easy to shape it. The wire was taped to a window, and the electronics
attached nearby.

I don't yet have pictures of the completed installation, but you might
be able to see it if you look at the east side of MacGregor at
night. I will post pictures as soon as I can hunt down someone with a
camera.

Later, a timer circuit was attached to make the wire blink instead of
glowing steadily. This circuit design is very similar to one that I will
present in a future tech note.

\section{Acknowledgements}
Albert Chiou, Bobby Liu, and Austin Clements were my co-conspirators
in this madness.

\nocite{elam}

\bibliography{21m735-tns}

\end{document}