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C H A P T E R T W E L V E
12.
Introduction to intelligent lighting
This section is for those who have not used intelligent lighting much
before, who are put off by dip switches, lights that move unexpectedly
and strange digital control systems that fly down microphone cables.
12.1
Ordinary lighting
Standard lighting consists of a variety of light bulbs connected to
dimmers. The lights may be anything from par cans to theatrical
lanterns, and the dimmer controls the intensity of the light. A typical
controller for standard lighting has a set of sliders, and each slider
controls the intensity of one dimmer using a low-voltage control signal
of 0 to 10 volts. The standard way to link the sliders to the dimmers is
by using a multicore cable with one core for each dimmer channel.
12.2
So what is intelligent lighting?
Intelligent lighting usually contains more functions than just intensity; a
typical intelligent light, often called a “fixture”, can also change colour,
project different patterns (called “gobos”) and direct the light beam in
any direction using a movable mirror or by motorised control of the
light unit itself. The fixtures are called “intelligent” because they contain
a small computer which controls the movement of the internal motors
in response to the control signals. Some fixtures can also listen to
music and produce their own light show, sometimes synchronising
themselves with other intelligent fixtures. However they are actually
not all that intelligent and usually need a user to make them do
something interesting.
12.3
How do you control it?
Each function of an intelligent fixture requires its own control signal, so
the user can select the colour, position, gobo etc. You can use 0 to 10
volt control signals on some fixtures, but the cable carrying the control
signals again has to be a multicore with one core for each function, so
each fixture might need 8 or more cores in the control cable. Some of
the more complicated fixtures use 20 channels.
When several fixtures are used, the number of cores needed in the
control cable soon becomes large. The cable also has to split at each
fixture. It all gets a bit complicated.
12.4
The DMX control system
Fortunately, there is an easy to use system for controlling intelligent
lighting and dimmers. It is called DMX-512, which stands for Digital
MultipleX, and it sends up to 512 control signals down a twisted pair
screened cable. The cable can be simply daisy-chained from each
fixture to the next. Microphone-style XLR connectors are usually used,
sometimes 3-pin and sometimes 5-pin. More recently RJ45 computer
network type connectors are being used.
The DMX system sends out the level for channel 1, followed by the level
for channel 2, then 3, then 4 and so on, all the way up to a maximum
of 512 (though not all DMX systems send out all the channels). It then
goes back to channel 1 again. All the units connected to the DMX
receive all the channels, and you tell them which channels to respond
