What is Virtual Grand Master?
Virtual Grand Master (or Virtual GM) is a software emulation of a Grand
Master stage lighting control.
OK, what is a Grand Master
The original Grand Master was a typical lighting control being
installed in theatres from the 1920s until the 1950s. It was made by
the Strand Electric Company Limited - the dominant lighting
manufacturer in the UK for most of that period.
Why should I be interested?
The way the Grand Master worked was heavily constrained by the
technology available at the time. In order to understand lighting of
the period, it is essential to understand theses constraints - and what
better way than to actually use a Grand Master to do some lighting?
This is not easy to arrange with a real Grand Master - there are few
left, and even fewer that are able to be used. And they are large, and
heavy, which makes them less than convenient for study. Enter the
Virtual Grand Master, which is operationally identical to the real
thing. You can either just play with it on the computer screen, or (by
using a LanBox) link it via DMX to real dimmers and lighting.
How does it work?
In order to understand the real Grand Master, it is important to
appreciate the limitations of the technology which was available at the
time. Dimmers used a variable resistance to alter the current through
the lamp, and the dimmer level was controlled mechanically by a lever.
This meant that any kind of presetting or memory control was not
possible: the dimmer levers were ‘live’ so that any
change had an immediate effect on the lighting on stage.
The Grand Master divided the total number of lighting circuits
(typically 40 to 80) into six groups, with the levers of each dimmer
driven by a shaft. Levers could be locked onto their shaft, so that
rotating the shaft drove the locked-on dimmers either up or down
depending on the direction of rotation. Any dimmers not locked on
didn’t move, while a clutch mechanism allowed the lock to
slip when the dimmer reached the end of its travel, ensuring that the
shaft could go on turning to complete the travel of any dimmers still
to reach top or bottom.
A further drive system linked all the shafts to a single Grand Master
wheel (hence the name) so that they could all be driven at once. The
gears could be set so that individual shafts would turn in either
direction or not at all when the grand master wheel was turned. Thus
one control could operate all the dimmers - a major advance over
preceding types of control.
Of course, there were substantial limitations; in particular, dimmers
on the same shaft could not move in opposite directions. Choosing which
dimmers were on which shaft was therefore crucial. At the time, wash
lighting with flood battens was usual, and these were often coloured
with the three primaries (red, green, blue) and white. Sometimes amber
replaced green. All the red circuits would be put on the same shaft, as
would all the green circuits, etc. Thus it would be possible to do a
cross fade from a red state to a blue one by setting the gearing on the
red and blue shaft masters to turn in opposite directions wheel the
grand master was operated. Odd circuits would be placed on the
Another significant limitation was that the maximum speed of a cue was
limited by the strength of the operator; on a large Grand Master with
all the dimmers moving in a cue, the mechanical resistance to movement
was considerable. A three second cue was probably a realistic maximum.
To provide snap blackouts, and to allow for a certain amount of
presetting just before a cue, individual circuits could be switched
either off, full on (direct from the mains supply) or via the dimmer.
In addition, master switches could black out the circuits on each shaft
separately, or the whole lot.
Virtual Grand Master replicates these controls, and if you
don’t have a LanBox, you can see the output in the Stage
Using VirtualGM with the
Virtual GM will communicate with the LanBox via an Ethernet connection,
using the UDP protocol. You can set the port number and IP address of
your LanBox in Virtual GM's Preferences window. By default, the port
and IP address are set to the LanBox's default values, so you should be
able to connect the LanBox, set your computer's networking settings
according to the LanBox manual's instructions for using UDP, select
"Connect via Ethernet" in Virtual GM's "LanBox" menu, and everything
Virtual GM is part of my PhD research into lighting control systems and
their relationship with lighting design and performance. For more
information, contact me or visit my web site (see below).
Virtual Grand Master is built with REALbasic, the object oriented rapid
application development tool for the Macintosh. It is offered as
freeware as both a built application and as source code, so do what you
like with it. Just don’t expect me to take responsibility for
Problems? Want to know more?
Contact me by email:
Or visit my web site:
Find out about the LanBox:
Find out about REALbasic:
Nick Hunt, April 2006