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Theatrical lighting

Introduction

Artful lighting design achieves many things at once; it illuminates the actors and scenery, creates contrast between foreground and background, indicates time of day and weather conditions, implies moods; it even allows the director to focus the audience's attention subliminally, perhaps on a particular prop or artiste, by subtle shifts in highlights. Te create this intricate light-picture it is often necessary to control the brightness (and sometimes colour) of a large number of lamps, perhaps many hundreds, with considerable finesse of timing and level throughout a fluid progression of 'scenes' or 'cue states' during the show. Art must be the master and technology the servant, but technology is often very much in evidence in theatre lighting. Many sophisticated electromechanical and electronic systems have been designed over the years to enable one or two operators to carry out all these functions smoothly and repeatably, at great expense in many cases. Until we have a chance to reveal these monsters, take a look at the other end of the spectrum of lighting switchboards.

Basic theatre lighting controls

Slider dimmer stage lighting boards

Stages such as those in schools and village halls could not justify complex and costly equipment to operate their small number of lamps on an infrequent basis, yet required the facility to switch or dim perhaps a dozen circuits of low wattage. For these applications most of the stage lighting manufacturers offered a simple switchboard built around individual resistance dimmers which could be assigned to circuits as required by a plug-and-socket patch arrangement. The dimmer sliders were operated directly by hand, without the benefit of levers and shafts to lock them together. This made the simultaneous dimming of many channels cumbersome and often demanded great ingenuity and dexterity. Wooden sticks could be used to push multiple sliders at once (as shown in one of Strand Electric's brochures!) or extra hands might be drafted in to operate individual dimmer handles for the more complicated cues. The advantage was simply economy; so long as the fixed wiring was there, dimmers could be bought or hired and added to the board using only a screwdriver.

Slider Dimmer

Slider Dimmer

The dimmers used on these boards were built in the simplest possible way, using resistance wire wound onto asbestos or slate formers over which the sliding contact runs. Unlike conventional wirewound variable resistors, lighting dimmers put more resistance into circuit per inch of travel near the bottom of the range than near the top. This enables a smooth fade with steady movement of the handle and in certain designs (termed variable-load dimmers) allows for flexibility in circuit wattage, which is nevertheless restricted to +/- 33% of the dimmer's nominal rating. Standard variable-load dimmers would suit 500 to 1000 watt lighting loads (e.g. one pair of spots with T1 lamps) but alternative ratings were available. The grading of the resistance requires either multiple formers which come into play in stages over the course of the handle travel, or sections wound with different gauges of wire jointed along the length of the former. The latter method, although widely used, was very troublesome. The medium gauge sections, which ran hottest, would sometimes sag and the turns would get crossed over and broken, while the finer wire at the bottom of the travel was prone to breakage and wearing through along the track where the sliding contact runs. In contrast, dimmers used on professional stages were constructed with individual resistance coils numbering perhaps 100, connected to brass studs over which the wiper arm would run, making for a smoother and much more robust dimmer albeit a larger and costlier one.

The switch configuration was generally standardised between manufacturers; if only one row of switches was provided each switch served to bypass the dimmer socket for that channel. This allowed more circuits to be on (at full) than the number of dimmers would otherwise permit. For example, a dimmer at zero could be plugged in, used to bring a circuit to full and then bypassed with the switch, after which it could be unplugged and used for another circuit while the first remained in use. A second row of switches was often included above the first, allowing channels to be switched between control under the master blackout switch, off, and independent. A group of channels could be snapped on or off with the master switch while others maintained a background state, for example, or a dimmed scene could be added without moving the dimmer sliders.

Strand HA20 stage lighting dimmer board

Strand HA board

Strand HA board

The archetype of slider dimmer boards. This board dates from the mid 1950's and was originally supplied by Strand Electric to a secondary school. The HA series comprised a range of modules, including 8-circuit and 12-circuit boards in a variety of frame styles, channel dimmers of two ratings, and optional master dimmers. The system could be ordered to suit the requirements and budget of the installation, with any number of dimmers up to one per channel. This unit is assembled from two standard wall-mounting JA-type frames and boards, one of 8 circuits and one of 12, giving 20 5-amp rated circuits connected to the fixed wiring with a maximum total load of 60A. Rewireable 'Dennis' fuses are fitted, below which are GEC 'Mutac' switches, chosen for their silent action, and 5A sockets by Sax. Although 6 Dimmers are present, all 500-1000W rating, there may originally have been more. The chassis layout was designed to accommodate one dimmer for every two circuits in a single row, which was a popular setup, a second row being installed below these if required. The dimmers are Strand's LS long travel type rated for 500-1000W, although later HA's used a different design as shown on the Junior-8' units below. This board has the 'luxury' of a board light, fitted near the centre and controlled by an extra switch. As received, the board was in a dirty and damaged condition, with incorrect fuseholders fitted on three channels, missing bridges, and dimmers in need of overhaul. The installer had also managed to shear many of the terminal screws on the back of the board. The overhaul is now completed although a few more fuse bridges have yet to be found and slotted in.

GB-Kalee 15-way board

Preceding the HA was this type of board, probably of late 1940's manufacture, badged in this case for the Cinema equipment manufacturers Gaumont British. Thought to have been used at the Haberdashers' Aske's school when based in Highgate, but actually found at the school in Elstree with no sign of having been used there. The fuseholders are MEM Kantark Junior type, the dimmer bypass switches GEC Mutac, and the sockets Contactum. The original dimmers were probably LS-type mounted on a separate backboard but these were not with the switchboard when found. What was with it, however, was the master dimmer rated for 8kW (or 12kW briefly) housed in an expanded-mesh case and operated with a wheel. This type of dimmer is actually identical to a channel-dimmer from a professional stage switchboard, and the difference in complexity will be seen when compared with a former-type dimmer. These were used with the later HA boards as well, for which a terminal box was provided in the standard frame. The master dimmer will need some cleaning up due to water damage (it was actually found in a puddle after severe flooding) but the switchboard is ready to go, just a few fuse bridges having been needed to replace missing and broken ones.

Strand Junior-8

Furse slider dimmer board

Furse slider dimmer board

Junior-8 was the last incarnation of the slider dimmer board, produced until electronic (triac) dimmers were sufficiently cheap to oust them in even the very lowest budget situations. Designed to be either permanently installed or portable, they control 8 5A channels paired on four dimmers, with the familiar GEC Mutac switch selecting dim / off / full, all under the control of a blackout switch on the right hand end. The patching arrangement is rather different to the boards shown above; instead of the switches being permanently wired to the lighting circuits and dimmers being assigned 'on the fly', the dimmers and switches are connected internally and the circuits plugged in as required using 5A 3-pin sockets on the front. This avoids duplication of sockets in portable applications whilst allowing a greater number of circuits than switches. There are traps here for the unwary, though, as the level of one circuit could be disturbed by adding or removing load from a shared dimmer. The fusing scheme allowed circuits up to 1kW when used individually on a dimmer but only 500W when paired to prevent overloading the dimmer, and hence limiting the total load to 20A. The use of cartridge fuses was a step forward in safety and convenience, particularly as the holders were of a touch-proof design unlike most of the rewireable fuse carriers common on the earlier boards. The dimmers are of Strand's final former-wound design which gave a nice dimming curve but was very prone to wire breakage, arcing and jamming. There were various optional units, such as the Master-3 which offered 3 short-time rated master dimmers to control 3 Junior-8 boards, or the Master-8 which offered one master dimmer for a Junior-8 plus two higher rated channel dimmers. In practice these units were rarely seen; any systems requiring three Junior-8's could probably justify a more sophisticated control system. Here at EK we have a number of Junior-8s in various stages of disrepair. They always seem to turn up with water damage or totally wrecked resistance formers, so a certain amount of mix-and-match will be required to get them working! A picture of the later Micro-8 electronic unit is shown for comparison; the functions are almost identical to those of a Junior-8 with the welcome addition of a master fader (easy to do electronically at little extra expense).

Furse 6-circuit primary dimmer board

Late 1950s / early 1960s lighting control from a different stable. Six circuits with six dimmers, but without the convenience of being able to operate them all with one stick, as they are in two rows for compactness! The upper row of toggle switches allows channels to bypass the master blackout switch (on the right hand side panel) or be switched off. The lower row of switches selects dim / full. One might suppose that the plug patch for the dimmers would be redundant when there is a dimmer for every circuit, yet it could be very handy for rearranging the dimmers so that any channels dimming together are adjacent and can be operated with less hands! The design of the dimmers themselves is good, with the resistance coils being spread over three formers. This allows heavier gauge wire to be used throughout, which along with well engineered wiper carriages and large brushes with low copper content, lends a smooth and quiet action to the dimmer. Maximum circuit rating 5 amps (1kW lighting load) protected by Slydlok rewireable fuses, dimmer rating 500-1000W. The board was recovered from a community centre stage along with some Furse lanterns during a rewire. Many of the switches and some of the fuseholders had been replaced with incorrect types and the dimmers were generally seized. Now in good order, complete with original heat-resisting dimmer flex.

History of theatre lighting - links

Further reading

  • Bentham, Frederick. Sixty Years of Light Work. London: Strand Lighting, 1992.
  • Ost, Geoffrey. Stage Lighting. London: Herbert Jenkins, 1954.
  • Wilson, Angus. Home-Made Lighting Apparatus. London: H.F.W. Deane & Sons.
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