Red Pages:

ROCTRONICS
STAGE ILLUMINATION SYSTEMS

for Theatres, Concerts, Festivals, Tradeshows, etc.


1. DIMMING SYSTEMS --- INTRODUCTION

The function of an illumination system is to give the lighting designer magical control over the audience's eye, and hence its mind ! The eye can only see by virtue of the light reflected by performers and scenery: No light, no vision, no perception. The two parts of an illumination system are the Lighting Instruments, which produce and direct light; and the Dimming System.

The purpose of the dimming system, is to permit the lighting designer to precisely control how much light falls upon each element of the stage.

Generally, the more brightly lit areas will command the audience's attention. Dimly lit scenes reveal little, forcing the mind to imagine that which it does not see. Darkness lets the designer conceal from perception that which he chooses to keep secret.

Purchasing a professional dimming system can also be an act of "magic" as some manufacturers purposely keep the buyer "in the dark". In this Red Pages section, Roctronics is pleased to "spotlight" ample information about features, power capacity, and cost.

1. DIMMING SYSTEMS ---HARDWARE
Dimming systems have two parts: The control panel and the power regulating dimmer packs.

The control panel may be foot or manually operated. They have multiple control knobs for adjusting the brightness of many Channels of lights. On the Foot Controls the knobs are rotary. On the Manual Panels the knobs are linear sliders. Each Channel feeds a brightness level control signal through control cable to the power regulating dimmer packs.

During a typical stage production it is necessary to change the brightness level of the many channels, too quickly for each channel to be adjusted individually. Hence the need for presetting different Scenes, or brightness levels of the many channels, in advance of the actual cue time. Transferring control from one preset to the next is called Cross Fading.

The lights on a channel may be flashed to full on by a bump button, or caused to flash automatically via Chase circuitry.

Low voltage Control Cables convey the brightness level commands from the control panel to the power regulating Dimmers. In a digital multiplex system, all the signals for the many channels travel along the same wire, time sequenced, to all of the Dimmers. Switches on each dimmer pack assign it to the desired channels. Hence only one wire need link all the Dimmers in daisy chain fashion.

The Portable Dimmers can be small and light weight, so they can hang close to the lighting fixtures, or they can be large rack mounted clusters. The small ones plug into standard 120 volt wall outlets. A 20 ampere outlet provides 2400 watts of power on one circuit breaker. Some dimmer packs have two plugs, which if fed from two different 20 amp circuit breaker outlets allow for dimming 4800 watts.

The Rack Mounted Dimmers must be fed via a 220 volt high amperage feed directly from a circuit breaker panel by an electrician.

The lights to be dimmed plug into receptacles on the Dimmer packs. U-ground Edison connectors are common,although 3-pin stage connectors are also available for the rack dimmers.


2. LIGHTING INSTRUMENTS --- INTRODUCTION
Lighting Instruments convert electricity into directed light to illuminate a performance area.

As electrons flow through the tungsten filament of a lamp, they cause it to heat up. The flow of electricity is measured in amperes or amps. The electromotive force driving the flow is measured in volts. The product of amps times volts is called watts, and is a measure of the total power being consumed. Most incandescent lamps in the United States operate at 120 volts. Most wall outlets in the U. S. can deliver 15 or 20 amps, as determined by the circuit breaker protecting that circuit.

Hence, 15 amps x 120 volts = 1800 watts or 20 amps x 120 volts = 2400 watts --- gives the maximum power available from parallel blade wall outlets. This is important because if the total wattage of lamps plugged into one outlet exceeds its capacity, the circuit breaker will shut down the power --- possibly in the middle of a show!

Each lamp is rated by the watts it will consume at its designed voltage --- usually 120 volts. How hot the filament glows is measured in Kelvin degrees. 3000 K gives a warm light, while 4000 K gives a cool blue white, sunlight is 5600 K. The hotter the filament the more light it radiates, measured in lumens. Also the hotter it burns, the shorter the life span of the filament --- you can't have more light without sacrificing lamp life! However, by filling a quartz glass bulb with halogen gas, tungsten atoms boiled off the filament will redeposit on the filament, not on the inside of the bulb. This both extends the life of the filament, and prevents light-blocking deposits from condensing on the glass bulb. Keep fingerprints off the quartz halogen bulb or it may shatter.

2. LIGHTING INSTRUMENTS --- HARDWARE

PAR CANS
So called because the reflectors of the lamps they hold are parabolic in shape. The fixtures are simple inexpensive cans, while the expensive lamps include both the filament, reflector and the beam spreading lens. They efficiently produce a soft edged oval of light.

FRESNELS
So called because they use the concentric ringed glass Fresnel lens to focus the light from a bare lamp. A spherical reflector behind the lamp increases the forward output.Unlike the fixed beam of the PAR lamp, the moveable lamp allows the beam spread to be changed.

ELLIPSOIDAL
So called because the optical path of the reflector and focusing lens follows the geometry of the ellipse. Unlike the Par or Fresnel, it can produce a sharp-edged focused spot. Shutters allow for shaping the beam to prevent unwanted spill. Zoom ellipsoidals can also change the beam spread. When ordered with Pattern Mask Slots, they can be used as powerful projectors of PATTERN MASKS .

BORDER or STRIP LIGHTS
Are long troughs of many lights, usually wired on 3 or 4 circuits colored differently, to allow them to color the backdrop curtain / cyclorama.

FOLLOW SPOT
Aimed by a person, it follows a moving performer. Like the ellipsoidal it produces a sharp edged spot, the diameter of which is adjusted with an iris; the top and bottom can be cut off with the shutter; and the color changed by a selection of color filters


3. PRICES ..... subject to change up to delivery.

DIMMING CONTROL SYSTEMS --- PRICES Oct. 1997

ECONOMY MODELS:

FOLLOWSPOTS For lighting moving performers

Order form


Copyright April 2, 1998 by R.. Iacobucci

ROCTRONICS
Dr. Iacobucci, Pres.
Roctronics Park
Pembroke, MA 02359 - USA
781- 826-8888
Fax us 781- 826-8889---24 hrs.
Email

[Main Page| Products|Services| ]