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A PRACTICAL GUIDE TO STAGE LIGHTING
cable. Two 1000-watt instruments, on the other hand,
equal 18.18 amps, and could be plugged into the #12
cable without exceeding its amperage rating.
Example 2: The dimmer is rated to handle 30 amps.
How many 750-watt instruments can be plugged
into that dimmer? This question could be determined
in two ways. The first method would use the second
version of the power formula to convert 750 watts
into amperage, and then divide the 30 amps by that
result: 750 watts divided by 110 volts equals 6.8
amps. Thirty amps divided by 6.8 equals 4.4 instru-
ments. In theory, the dimmer could safely carry 4.4
instruments, but practically, it can only carry four
750-watt instruments. The second method would
use the first version of the power formula to convert
the 30-amp dimmer into wattage. Thirty amps mul-
tiplied by 110 volts equals 3300 watts. If that result
is divided by 750 watts, the result is again 4.4 instru-
ments. Either method arrives at the same result.
One rough rule of thumb used is that each 1000-
watt instrument is roughly equivalent to 10 amps.
(In reality, it’s just above 9 amps.) Using that rough
yard stick, how many 1000-watt instruments can be
plugged into a 12-pack of 20-amp dimmers? 12 times
20-amp dimmers equals 240 amps. So, using the
10 amp rule of thumb, the rough answer? 24-1000-
watt instruments should not overload the dimmer
pack. (In reality, 24 × 1000-watt instruments, divided
by 110 volts, equals 218 amps. Safely under the 240
amp limit of the dimmer pack.)
Rule of thumb two: How many amps are needed
to power 15-1000-watt instruments? Rough answer:
15-1000-watt instruments equals 15 × 10 amps each,
or 150 amps. (In reality, 15,000 watts, divided by
110 volts, equals 136 amps. Safely under the rough
150-amp calculation.)
When possible, the production electricians load
calculations on a dimmer system should be a dou-
ble-check of prior calculations made by the lighting
designer. On larger shows involving multiple dimmer
racks and power sources, however, load calculations
become an exclusive part of the production electri-
cian’s domain. If the lighting designer possesses a basic
knowledge of electricity, though, he or she will be able
to make certain that the designed light plot can be
physically realized without on-site power limitations
imposing last minute restrictions to the design.
Since electricity is the element that allows the-
atrical lighting design to occur, the lighting designer
and all members of the lighting department must
be aware of its attributes, and the fact that it’s dan-
gerous. Electricity can easily cause injury or death.
Knowledge, caution, and common sense are the basic
tools that should always be practiced during any
time spent on a stage. And that is doubly true when
electricity is involved. This text presents some of the
basic laws and principles about electricity, but other
texts more closely analyzing this topic are worthy of
examination. A sampling of them can be found in the
bibliography.
CONTROL
Two general terms are applied in theatrical situations
where dimmers control voltage to lighting instru-
ments or devices. Manual control implies physical
movement of a handle, lever, dial, fader, or slider to
affect a dimmer. An autotransformer light board is
an example of this control type. Moving the single
physical handle up or down, directly affects the volt-
age supplied to an instrument, and makes the light
brighter or darker. “Handle” has now been adapted
as a generic term, referring to anything that affects
an instrument’s intensity. Computer control, on the
other hand, implies an electronic interface with the
dimmer rather than a physical one. In most cases
the dimmers are affected by commands issued from
a remote device with keypads called a computer light
board or a computer lighting console.
The term “control” is also used to describe the
numerical arrangement of the channels or dimmers
that regulate instrument intensity. When a light plot
is constructed, the lighting designer decides which
instruments will operate together, which separately,
and how they will numerically relate to each other.
Their arrangement is documented in a form called
a hookup. The word “hookup” is an anachronism
carried over from the days of manual road boards.
The physical action of plugging cables into the
dimmers meant the cables were being “hooked up”
or “patched” to the dimmer boards. The word is still
used today, but when used in conjunction with light-
ing systems controlled by computer boards, the word
“hookup” also refers to the action of electronically
assigning dimmers to control channels. This action is
also referred to as softpatching.
That has resulted in a linguistic back construc-
tion for the older system of physically plugging the
cables into the dimmers, in order to provide control
to a lighting instrument. That’s now called hard-
patching. If an instrument is plugged into a cable or
circuit that’s hardpatched into dimmer 1, then the
instrument will turn on when the handle or fader for
dimmer 1 is manually brought up.
With a computer lighting console, on the other
hand, no matter what dimmer the instrument has
been plugged into, the dimmer can be assigned to any

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