A Practical Guide to Stage Lighting, 2nd Edition

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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 electrician’s 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