FREDERICK BENTHAM Theatre Consultants Services, London

Control and stage

The key to is control-optical, mechanical and electrical. Taken really seriously what we have to do is not just to illuminate the stage but to paint a picture with light. Before long that picture has to be replaced by another. This second picture may differ totally from its predecessor or but so slightly as to represent only small change of accent-a stressing of one area or a playing down of another. The tempo of such a change will have to range from the twinkling of an eye to a languid, virtually imperceptible creep. The use of the expression, ‘ paint a picture with light ’ suggests an artist in charge, but this is rarely achieved. It is a sad feature that specialist lighting designers may be skilled in the art of stage lighting but they are neither artists nor is what they do Art. They form one of a team concerned with the mechanics of putting a play on. Strive as we may, the various technical developments over the years, instead of making it easier for the artist to take over, in fact put him more and more in the hands of such a specialist. The artist sees the possibilities but he is scared off by the cumbersome complications of lighting as a medium. Nevertheless I and a few others like me have continued to work on the assumption that an instrumental approach is possible and that an artist should be able to sit down at some console vaguely related to an organ in form, there to function like an accompanist to fill in the essential link between the actor, the scenery and the audience’s eyes. On rare occasions one feels the message might be got over better with just light and the scenery. The lighting in that case almost takes on a solo role: I say ‘ almost ’ because when I have gone that far it has always seemed necessary to have music. Such variations for lighting and music can be conveniently called ‘ colour music ’ and may be regarded as fun for the switchboard operator to train on and certainly as an excellent means of trying out and demonstrating a new lighting control. It could well be that frustration, at the lack of a safety valve in the form of such ‘ solo ’ lighting, accounts for the overuse of lighting in some stage productions. Then again in the ergonomics of the equipment provided there may be a tendency to design for all contingencies, whereas if one applied the maxim, ‘ don’t worry, it may never happen! ’ the facilities provided might be easier for ordinary mortals to understand. There is an obvious point which may get overlooked. Because light cannot perform in limbo, it is much harder to design an instrument to play it than one to play sound. Our installation completed, all we are left with will be a hundred or so meaningless patches of light awaiting a show on the stage which will tell us where to direct and how to focus them. Indeed, quite often all we are left with is a lot of circuits terminating in socket outlets. Electrically live they may be, but this does not make them come alive! With this in mind let us see where this type of theatre equipment has in fact got to. Stage lighting can be said to have begun in 1881 when the new Savoy Theatre, London, opened with the Gilbert and Sullivan opera, Patience. It is not the lighting required for this opera that makes this date important but the fact that for the first time anywhere an entire theatre was lit by electricity-using in fact Swan filament lamps and Siemens equipment. A good contemporary account of this installation appeared in the journal

225 Frederick Bentham

Engineering of 3 March 1882. The account shows the theatre’s need even then to fade lights in and out with dimmers (of which there were six) rather than just to switch them on or off. In order that this article may become an eyewitness account, it is convenient to jump to 1932 and the opening of the Shakespeare Memorial Theatre (now known as the Royal Shakespeare) at Stratford-upon-Avon. There were 56 dimmers-a rather low number for a theatre of this importance. Indeed seen at this distance the stage lighting installation as a whole was very modest and an equivalent theatre of that time in Germany would have had about double the amount. The switchboard was a large cumbersome affair due to the British practice (which took an unconscionable time a-dying) of mounting the dimmers directly behind their operating handles. A lot of theatre electricians derived great comfort from the stout metal links joining the two. Except that in this case eight of them were liquid type and had to be operated remotely by tracker wire, all the rest were metal resistance. The supply was 230/460 V three wire DC. Where, as here, there were relatively few lighting circuits, dimmers were used mainly to fade from one lighting picture to another which accounts for the very crude mastering arrangements. Individual levers could be locked onto their shaft by a half turn of the handle and the big wheel turned from the centre. In any case extra labour to help push a few levers was readily available. No finesse was possible because the whole contraption was very large and therefore mounted out of the way on the side of the stage, with a rotten view therefore of the effects it produced. This kind of control survived a long time both here and in North America, although more sophisticated (but more expensive) equipment soon became available. During the 1930’s one had the frustrating experience of watching theatres rewire and instal new switchboards of this old type, at supply authority expense, to cater for the changeover to three phase AC. It might be thought that the first task was to get rid of resistance as a means of dimming but although autotransformers became common in Germany the energy saving was of little account compared to the increased capital cost. There was no subsidized theatre in Britain in those days. Nor was the facility of dimming a variable load to the same curve considered all that important. What was required was to reduce the size of the switchboard so as to turn it into a compact control panel or console-the load carrying dimmers and switches simply had to be remote from their controls. The German theatre achieved this with massed runs of tracker wire terminating in a compact regulator with a number of ingenious mechanical devices for mastering. The centres at which the levers were mounted went down from four and a half to one and a half inches. The real solution, however, was to have an electrical rather than a mechanical linkage between the dimmers and the control panel. There were two possibilities: a servo system operation of resistance or autotransformer dimmers or else an all electric system where there would be no moving parts. In fact the next lighting control the Stratford- upon-Avon theatre was to have was of this latter type. The dimmers were valves, used directly in the lamp circuit and grid controlled remotely by a . Many years earlier indirect providing the saturating current for load carrying reactors had been used in the United States for occasional prestige installations, the most famous of which was that in Radio City Music Hall. Installed in 1933 and consisting of 314 dimmers, it is still in use. The Stratford thyratron installation was put in for the summer season of 1951. There were 144 dimmers and although the control panel was duplicated (figure 1) it was still compact enough to be put into the Royal Box in the centre of the Dress Circle. It can be Control and stage lighting 227 appreciated that this position alone, no matter what the additional control facilities, represented a great step forward; the operator was able to see the effects produced on the stage. However, the duplicate panels with their massed control levers at one inch centres were also very important since this arrangement enabled one lighting picture to be held on the first panel while the second was being prepared and vice versa.

Figure 1. 144 thyratron dimmers remotely controlled from a two preset desk. Similar to Stratford 1951.

Although the thyratron installation remained in use until the end of 1971, it was rather temperamental and turned out to be more wasteful in use than a corresponding bank of resistances would have been. The trouble was that the heater filaments of the valves represented a considerable load since they all had to be on continuously ‘ at the ready ’ whether the circuit was in use at the time or not. Much puzzlement was caused at the time by the fact that these rooms were so much warmer than resistance dimmer rooms until it was realised that there was roughly the equivalent of a 10 kW fire burning continuously. There followed in consequence a revival of interest in the servo, and a golden decade of electromechanical remote control followed in this country. The system used was decidedly primitive but it was very reliable : iron wheels on a constantly revolving drive shaft were gripped by pairs of electromagnets and linked to cranks above and below the dimmer pivot to provide reversal. As many as 120 dimmers would be mounted in four or five tiers as one bank and driven by one variable speed motor. A large installation would have two such banks. The dimmers were controlled for position by feeding the clutches through a polarized relay Wheatstone bridge circuit. This kind of electromechanical servo had one great advantage over an all electric system-the control circuits did not need to be continuously energized to hold station. One could set the individual dimmer levers to the various levels (intensities) required and then set the drive in motion, wholly or in part. When the change of picture was completed the operator would disengage and reset. Attracted in the early 1930s to the John Compton Organ Company’s stop-key console, electromagnetic relay action and the method of wiring used for their organs (particularly for cinemas) I had carried out full scale experiments applying these to lighting control. It was an excellent basis for stage and television lighting controls during the 1950s and a couple of hundred installations were completed. One organ 228 Frederick Bentham feature which was particularly useful was the instantly adjustable combination action, This could select a group of stop keys and thus make their individual dimmers move or not. These became known as ' memories ' and helped relieve the operator of much finicky dimmer lever work because he only had to concern himself with circuits in which the level of light had to change. Also by putting one side of the control end of the servo network down to negative or positive, one could bypass the dimmer levers altogether if intermediate levels were not wanted or not critical. The search for alternative static dimmers to the thyratron went on, and in America and Germany the magnetic amplifier (a sophisticated form of saturable reactor giving infinite load variations) was extensively used, while we in this country only used the basic form in order to keep the cost down and make some sort of remote control possible even where price was all important. The development of the (or silicon controlled rectifier as it was first known in the United States) changed dimmers dramatically. Here was a very compact, solid state equivalent of the thyratron which could not be neglected. The first really large installation in Europe had 240 5 kW dimmers and went into service in the Royal Opera House, Covent Garden, in the summer of 1964. Characteristically this electronic set-up was controlled by the Compton ' memory ' relay action-wooden boxes and all-due to our reluctance to lose all the unique ' inertia ' qualities of the electromechanical control systems. Within a year the cost of thyristor dimmers was halved and this, plus the compactness and a lack of moving parts, soon made them ubiquitous. Up to about 80 dimmers, it was convenient to mount the dimmer levers in two or three rows; each row representing an alternative holding supply, Thus 80 dimmers would normally be represented by 240 levers. A master fader associated with each row enabled rows to be added together or substituted one for another. Such an arrangement is referred to as a three preset control. To avoid the use of all the levers of a preset for a rather local change it is customary to provide two or three masters per preset and a selector switch over each individual lever to ' group up '. The Compton ' memory ' action just referred to in the case of Covent Garden Opera House does this semiautomatically by enabling the groups to be transferred (parked) from their master to a holding busbar-a fact which is indicated by illuminating the dimmer scales internally in appropriate colours. Convent Garden has in fact four presets which means 960 levers and there are 50 memory groups. Without these memory groups the number of presets would have had to have been increased. The more dimmers there are, the longer the resetting time so the more presets there have to be to store the stage pictures. The process becomes self defeating as witness the control system in the new Metropolitan Opera House, Lincoln Centre, Nkw York, where ten presets for 360 dimmers literally paper the walls with miniature levers. Then again an immense amount of writing down (plotting) has to take place so that the lighting arrangements which produce the pictures can be repeated. The solution, long sought, is to set up a picture and then record it for subsequent repeat. One method and the first to take the field was of course to use punched cards, but magnetic recording has now supplanted it-though in Germany in particular there are an appreciable number of such installations. Whether the cards are read automatically or placed in alternative readers by hand is of little importance but they must be punched automatically to be at all convenient. Cards have the advantage of easy storage; a production can be taken out of a cupboard and used right away. It is a feature of all opera houses and of some theatres that they play their productions in repertoire. This Control and stage lighting 229 means that tonight’s show will be different from yesterday’s or tomorrow’s yet a number of repeat performances will be given over weeks or perhaps years. Thus when ferrite stores were adopted to hold the memory, an additional form of recording storage became necessary to record a production for shelf storage. Punched tape and latterly magnetic tape cassettes are now used but the development in this field has been great and of recent date-as the reader will be well aware from his or her own experience. I shall try therefore to confine myself to the peculiarities of adaptation for theatre.

Figure 2. 120 thyristor dimmers with single set of levers on left and instant memory recording and playback controls on right. Haymarket Theatre Leicester 1973.

In part these spring from the conservatism and traditionalism of the theatre. This conservatism may be rather hard to swallow against a background of Godspell and fringe productions in which ‘ streaking ’ is practised in show motion as it were, but the word does apply to the technical staff; it probable springs from their normally poor training- a kind of sublimal apprenticeship. Then again these technicians are people drawn in the main into the theatre by the very qualities it does not have in common with engineering and science. The term ‘ memory ’ has now been carried over to cover the storage not only of groups but also of dimmer levels-say 32 discrete steps of intensity-and the most obvious form adopted for a lighting control incorporating this facility is a single complete set of dimmer levers (figure 2). With these an operator can set up his picture by eye in the familiar way. This information is then converted from analogue to digital and ‘ filed ’ magnetically as a ‘memory’ number or address. The picture represented by that number may need to be retrieved from a random order, particularly during rehearsal, and have to be combined in varying proportions with other pictures to form a composite picture. It is as if one takes blocks (or choruses) of this and that, instead of solo circuits. The organ analogy is inescapable! This combination, the playing of memories against or with each other, may have to go on during performance. If one imagines groups of actors making entrances from time to time in various areas of the stage, each requiring their own illumination while at the same time there is a very slow, progressive increase in the light overall (as in a dawn) it can be seen that the problem is one of synchronization. For example, if group B is to enter halfway through the dawn, it is no good quickly subsituting the next picture (lighting for B) when the overall dawn itself may not have progressed as far as it has C 230 Frederick Bentham in the content of that new picture; the two would not match and a jump or a rush would then become apparent. Matching is also required in another respect. It may often be necessary to take circuits over from their recorded picture, to adjust them manually-tweak them up or down a bit-and put them back. This requirement is obviously complicated if positional dimmer controls are used for manual operation. One German manufacturer has rather ducked this problem by fitting all dimmer levers with servos so that the memory action operates these and hence the lights on stage. It can be seen that what began as a simple problem-how to provide an orthodox stage control with a memory (in effect a large number of presets without using more than one set of levers) leads on to a far deeper consideration of what we need to do. The higher the degree of computation available in the electronic logic the more we find ourselves wanting to do. The ultimate is represented by the use of a standard minicomputer (a PDP 11) suitably programmed to service the various terminals. This method was adopted for the first time in theatre for the third and latest of the Stratford-upon-Avon controls-that of 1972. There are now 240 dimmers (thyristor of course) and except for a final conversion to analogue to operate these, the whole of the action is digital. It is important to establish that the use of the standard computer arose from my ergonomic demands rather than any knowledge I then had of these things. More and more as I tried to work out the logical ergonomics for a memory system for a theatre of this importance, it became apparent to the engineer trying to turn my wishes into electronic reality that a software program was the only answer (figure 3). By now a number of these controls (known as System DDM) are in use, with more or less my original program, but for the new National Theatre in London another program will be used, devised by another consultant.

Figure 3. 240 computer controlled dimmers. The author is seen operating lighting to test and revise software program before installation in Stratford-upon-Avon 1972.

This shows the value of the software approach but also its drawback. Until now the nature of the hardware we had to assemble to make a lighting control tended greatly to influence what we could do; also the pace of development was relatively slow. The switchboard in a theatre would therefore be largely familiar to any operator and he would feel at home with it very quickly in spite of an unfamiliar arrangement of the lanterns. Nowadays however the form of a switchboard may be governed only by the Control and stage lighting 23 1 logic of a particular switchboard designer and there can be as many ergonomic logics as there are designers. Thus at the very moment when at last the operation of the lighting should be easy, the sheer unfamiliarity of the controls of one manufacturer and another-or even variations within the work of a single manufacturer-will make a course of instruction necessary when transferring from one theatre to another. The operator has to become more of an expert in order to work today’s ‘ simpler ’ switchboards! The fact that standard electronic ‘ bricks ’ can be put together to make dimmers and dimmer controls means that more firms can dabble in this area than in the days when specialist mechanical engineering was involved. My own firm, Strand Electric, was without any rival in the days of electromechanical servo dimmer banks. Nobody wanted to be bothered to take up that challenge. In much the same way over the years if one wanted the servo at the dimmer lever end, then Siemens were and are your firm. However, once one has a full dimmer memory, even the traditional dimmer lever becomes suspect. It is true we require a means of increasing and decreasing light but this could be achieved by ‘ raise ’ and ‘ lower ’ push buttons. Ideally these would be incorporated into the one rocker unit as was done in the case of Stratford-upon-Avon. The actual holding of the dimmer to its intensity level can be done by the computer stores. The computer itself has to store (or memorize): (i) Its own program-the way it is to behave-for ever. (ii) The lighting pictures for the show whenever it is on the stage- a matter of three or four hours. (iii) The transitory states concerned with modification, or computation, for a matter of perhaps only minutes or even seconds. This ‘ holding’ ability is automatic and frees the operator from the need to do anything about it. It is the modern equivalent of the ‘ inertia ’ of the earlier mechanical systems. The operator has only to work in terms of change. Mind you there are various forms of change, the commonest being ‘ crossfade ’ in which one picture replaces another usually with some ingredients common to both ie which do not have to alter in intensity. Even here the operator has to make the decision: are the incoming circuits to make their presence felt faster than the departing ones proclaim their absence ? Another form of change adds two or more pictures together and here the question arises in the case of common circuits at different levels on the added memories: should the highest or the lowest take effect? This is but a taste of the area for discussion and experiment now opened up, though the few people qualified to think and talk lighting control do indeed form an esoteric group. There are those who pin their solutions wholly on a numerical basis (figure 4) as indeed seems to be particularly logical when dealing with any form of computation. Individual dimmers are then called up just as the memories are by means of a version of the calculator keyboard which has become so familiar-if one may add, so recently! Such an arrangement drastically reduces the number of dimmer controls. Instead of say 200 rockers there would be but 10 keys. One has to be careful, however, a feature of individual controls is that they can be used to provide good indication of what is happening. If in action they light up, a glance from the operator can sum up the whole situation. My rocker controls for example constitute a kind of mimic diagram which itself not only shows but actually performs operations. I would have liked to see the 232 Frederick Bentham

Figure 4. Numerical call-up of dimmers instead Figure 5. Backstage theatre, Royal Drury Lane of individual control of each. This system is 1972. 216 resistance dimmers servo operated, modular. Each panel carries combinations to originally installed in 1950 were used for this suit each particular theatre or television studio. production. memory controls take this form as well. It is now proposed to use in the case of the National Theatre visual display units of the television type to give this information. I find the display of the ' doings ' away from the area of doing it, a rather backward step. I hope the operator is not going to find himself working head down in the office among the figures with only an occasional glance at the stage. The privilege of a view of the stage as others, his audience, see it has only been won with difficulty. All this is beyond discussion here. Certainly it can be said that we are at last free to decide what form we want a stage lighting control to take and whatever the form it does take, however misconceived, it represents an immense step forward in facility. However, the best controlled dimmers in the world depend absolutely on what is plugged into them. The lack of progress here is quite extraordinary. Anyone who knew stage lighting equipment 40 years ago would be equally at home with it now. He would find much more equipment used (see figure 5) and some of it would now be mass produced. The basic units may be a little smaller, wattage for wattage, but the optical systems would only be superficially different. Even the method of colouring the light would be the same. Filters, then of dyed gelatine but superceded about that time by self extinguishing cellulose acetate, remain the common method. Even if the most recently introduced polyester sheet does take over it will still be a filter-a light waster. Also it will still be impermanent and even if it were not someone would still have to visit the lantern itself to change it. This journal would seem to be a good place to remark on the curiously static nature of the optical control of light-all the principles seems to have been determined a long time ago. The Fresnel lens was invented about the same time as the resistance dimmer and yet that lens (stuck in front of a lamp which can be moved to and fro relative to it to contract or expand the beam) is our staple in stage lighting. The magic lantern was invented goodness knows when, yet what we do whenever it is necessary to frame the light exactly to cover the profile of an object or to project a scenic picture, remains much the same. To be fair, profile spots use a reflector to collect the light, rather than a condenser lens, and direct it on the gate carrying the framing shutters or iris, but that too happened in the 1930s. A 2 in x 2 in slide projector like the Kodak Carousel and the quality photographically of the colour transparencies do represent a great advance but this is obtained by forced cooling of the lamp, the noise of which rules such units out except in rather special circumstances. The more recent tungsten-halogen lamps Control and stage lighting 233 have decreased the size of the source while maintaining its light output throughout its useful life-but watts remain obstinately watts. Theatre people have remained faithful to the tungsten filament lamp due to its freedom from auxiliary gear. Discharge lamps of various types which could produce better efficiencies, and even coloured light at source, have never taken hold in the theatre. The great revolution has passed us by, a long low brightness source is useless. What we have to have is compact high brightness sources which dim right down to out when the line volts are dropped. Incidentally if anyone wishes to take up the challenge of optical systems for the theatre I know who to put him in touch with! Surely now that computers make light work of the calculations there could be some sort of breakthrough! A compact source lamp of exceptional efficiency (90 lm W-l) like the tiny mercury halide arc tempts one to wonder whether this should not be more extensively used but the auxiliary gear complication and the need for servo operation of the shutters to dim it are bound to restrict it to the few manually operated spotlights used to ' follow ' the stars around the stage. In a sense, however, all stage lighting is manually operated in that it has to be coloured up and directed on target as required. The bulk of such equipment conforms to the designation ' spotlight ' and the direction and focusing has to be precise indeed. They are then locked into position and the switchboard takes over but of course its control is limited to switching on or dimming. Remote controlled movement of any kind would bring us back into the theatre of the mechanical servo and to do this in respect of a hundred or so spotlights is out of the question. In the case of a Fresnel spot this would involve pan, tilt, and focus. In the case of a profile spot the five gate shutters have to be added and we would still not have got over the problem of colour. Television studios do use a detachable pole to operate the three functions on their Fresnel spots but the majority of theatre lanterns have to hang too high to make this feasible. If one considers the obvious point that lighting equipment must not get in the way of the actors or of any of the changing scenery and yet must cover both of these from as many angles and directions as possible, it is not surprising that so much of it is difficult to get at. Quite a considerable amount comes from the direction of the audience and therefore is situated in the roof and on the side walls of the auditorium. Incidentally a reminder is necessary that sometimes an audience may not just confront a stage at one end but surround it on three or four sides. These auditorium positions usually take the form of lighting bridges either concealed above slots in the ceiling or in full view according to taste. In either case they are not usually available for access when the audience are in, for safety reasons. Backstage lighting bridges are much less used due to the obstruction they cause overhead. A traditional way of changing scenery is to fly it in or out vertically. Lighting equipment is therefore likely to hang from horizontal pipe barrels overhead and vertically at the sides. The compromise arrived at is in some cases to provide lighting bridges for access but mostly it is a matter of a ladder or some refinement on that. So there we are- a gentleman in a tuxedo caressing the keys of his computer control at one end, and a bloke with his mate on a long ladder fighting a nearly red hot spotlight at the other-that is stage lighting in 1974!

Acknowledgments

The author wishes to thank Rank Strand Electric Ltd for permission to reproduce all the illustrations in this article.