11

Motorised lights

 

Introduction

Motorised lights were introduced on a large scale for the disco scene closely followed by the pop groups on tour, for road shows and live concerts. The idea of moving the light beams by either a mirror or moving the luminaire was a progression from purely placing colour and patterns in them. Eventually, TV and film borrowed the techniques to create, in their own media, a simulation of a live pop show.

The technical designers of lighting soon discovered that the pop/theatre and TV requirements were poles apart. The pop and theatre industry required extremely fast movement for effect with as many colour changes as possible, using multi-layer dichroic filters, all combined in a lightweight portable unit that could be rigged on overhead trusses. Theatre and TV systems do not always require the same degree of speed and number of colour changes, but do require accurate positioning. This is highlighted in the case of a motorised spot luminaire, with hard edged focus. With a projected distance of say, 10 m, the beam must stop within a repeatable accuracy of at least 10cm.

In the case of Fresnel or PC luminaires, focusing from flood to spot does not require a great accuracy of setting, similarly hard edge to soft edge focus on a profile spot. In TV a motorised Fresnel with a set of barndoors requires movement of the four barndoor flaps together with clockwise/anticlockwise rotation. A colour changing system is an essential requirement, with a suggested minimum of 20 colours, which may be provided by a colour scroller or built in filtration. In a profile projector, two lenses have to be moved to change the spot size, a set of shutters with some degree of rotation are required to shape the beam with optical adjustments to produce the beam distribution required.

The acoustic noise associated with movement and accuracy of alignment can be overcome by either reducing the speed of movement, or by using very high grade drive systems. Motorised luminaires in TV are not always intended to stimulate emotional effects; the aim is to produce fast turn round times in a studio.

Ask any LD for a desirable list of requirements for a motorised luminaire and they will certainly cite all of the above controls, plus many personal foibles. They would also like to control the luminaires by standing in the middle of the acting area, pointing a magic wand at the appropriate luminaire and creating any number of effects. Added to these requirements is a memory system that would record every movement, the time of that movement and the position of the end result.

11.1 Luminaires

Modern fittings are capable of rapid lighting changes and although one light may be capable of several modes, by moving the beam around the acting area we get several incident light angles. As Francis Reid has said ‘one of the most important aspects of lighting is the angle at which the light beam hits the artists’. From the point of view of changing the beam shape, light output and colour, there are many useful features in the modern generation of motorised luminaires. The multiplicity of colours available for one luminaire may obviate the use of two or three for effect (see Figure 11.1).

Figure 11.1 Motorised luminaire (courtesy of High End Systems)

There is a need to shape the light beam in many ways and to introduce a multiplicity of colour effects. In the luminaires provided by some manufacturers the movement of the light beam is created by the use of mirrors. Mirrors are used because they are extremely lightweight devices in comparison to the luminaire itself and to move luminaires at high velocity to achieve rapidly moving effects, requires sophisticated drive systems. For TV, the movements required are usually slower due to using larger luminaires.

With a motorised ‘pan and tilt’ mechanism, it is possible to remotely focus the luminaire. On the surface this seems relatively straightforward to achieve but there are several snags that have to be watched for and these are:

(a) What is the speed of motion required?

(b) How is the speed controlled?

(c) Is it variable and does it have a finite maximum to avoid any structural damage to any component parts of the luminaire?

If the speed is too low it will be annoying to the operator controlling the result, and if too fast probably not very well controlled. How far do we take the directional movement? It would obviously be quite ludicrous to have a device that allowed the ‘tilt’ mode to keep travelling in the same direction and thus rotate within its yoke. This would cause rather a lot of damage to any power feeding cables or control cables for that matter. By the same token the ‘pan’ has to be restricted in some way with a feedback system that tells the control that it has reached a finite distance of travel. It is suggested that for ‘pan’ the motion must be restricted to just over 360° to cover for all situations. Is the device equipped with a system that allows control of ‘pan and tilt’ simultaneously and does the device have sufficient intelligence to work out its final destination from two co-ordinates being provided. Perhaps most important of all is how accurately does the device position itself and how noisy is it in operation?

As an example, let us take the case of an effects luminaire with a beam width of 30° with a throw of 10 m: the beam diameter would be 5.36 m. On the assumption of an error of 50 mm at the edge of the beam would not produce too disturbing a result, we discover that this would be caused by the beam being misaligned by 0.29°. In the world of digital electronics where the binary system is used, we find that 2 raised to the power of 10 gives 1024. As this would be a convenient number to use within our digital electronic control system, if we divide 360° (the maximum rotation within one full circle) by 1024 we discover it produces 0.35° and in fact most of the systems in use today work to an accuracy of roughly this amount; usually, in most manufacturers’ literature, called ‘one third of a degree’. This error, applied to our original beam at 10 m throw produces an error of 61 mm, which is just over 1% of the width of the beam. Obviously as the beam width becomes narrower, the proportion of error in relation to the projected beam is greater. With wide beam luminaires, the result would not be so noticeable. The accuracy of the electronics involved is still, however, greatly influenced by the mechanical coupling of the systems themselves and if much slack exists in either the ‘pan’ or ‘tilt’ mechanism accuracies such as those discussed will not be attained. The practical limitations of ‘pan and tilt’ would appear to be a fraction over 360° in ‘pan’ and 270° for the ‘tilt’ operation. One point to be observed when going through the ‘tilt’ angles is that it would be quite possible to exceed the lamp manufacturers stated operating angles when using tungsten halogen lamps, although possibly quite satisfactory for discharge sources. Because a fixed speed of movement would be a disadvantage it is preferable that it is a smoothly controlled variable, governed by the control electronics. One manufacturer publishes figures of a minimum velocity of 0.5°/second, and a maximum velocity of 120°/second, which translated into more meaningful terms means rotations varying from 3seconds in duration to 12minutes. Measures should be taken so that in the event of hitting an obstruction the unit will not drive against a motor. This avoids the possibility of either damaging scenery, the luminaire body or burning out the motors.

Having adjusted the ‘pan and tilt’ so that the luminaire is pointing in the right direction, or the direction of reflection from the mirrors, what type of beam do we require? There are two ways of varying the beam angle of a luminaire; one of which is to adjust the lamp in relation to the optics to give varying outputs. This would be the case with Fresnel lens type luminaires. If we were focusing projector type luminaires such as the profile spot, it would be desirable to have adjustment of the optics or if fitted, zoom optics, thus being able to give a continuously variable beam angle over the operating range of the optics. Another desirable feature on a luminaire is that we should be able to have a soft or hard edge to the light beam. With all types of luminaire in use, patterns or ‘gobos’ will be required and these should obviously be inbuilt to the device so that they are instantly available upon selection.

Many of today's effects luminaires are often fitted with discharge lamps; if this is the case and they have to be integrated with other units, it should be borne in mind that their colour output will probably be around 5600 K and to match with other sources within sets, they may have to be colour corrected to 3200 K. By utilising special short arc discharge lamps a very high light output is gained and, in fact, almost doubled for some luminaires.

Even allowing for the colour of the source, we would wish to change the basic colour of the light output for effects. There are two ways by which this can be accomplished, one of which is to put electromechanically driven colour changing units on the front of the lumi-naires or have integral colour changing usually accomplished by a ‘dichroic’ system. Electromechanical colour changers are invariably noisy whereas the use of integral dichroics may be less obtrusive from the point of view of acoustics. A dichroic colour changer has to be able to feature a wide range of colours; one manufacturer gives a range of 120 different colours.

If we are using tungsten luminaires obviously these can be dimmed by electronic dimmers in the normal way. However, if we are using discharge sources, even if they were of the ‘instant restrike’ type, they always have to go through a period of colour and intensity change upon any degree of warming up after being activated. Generally discharge sources require separate mains supply and do not work satisfactorily from dimming circuits, therefore the most satisfactory method is to use a mechanical dimming shutter to control the light output. This possibly would take the form of an iris which works in a similar manner to that of a still camera. Although the iris would give good control of the light beam, we would have to allow for complete blackout for effect and the time from maximum ‘open’ to maximum ‘close’ has to be carefully controlled. Two variations of operation occur, one of which is the appearance of the luminaire having been switched off, which implies a very rapid shutdown of the iris, or it might be programmable over a long period of time to give the effect of a very slow fade, as used in the theatre world. Being a mechanical device, it once again is a source of acoustic noise (see Figure 11.2). Motorised lights project patterns, colours and mixtures of the two. Most motorised light luminaires are usually fitted with a rotating gobo wheel and a fixed gobo wheel. A fixed gobo in position is fixed relative to the optical axis, whereas a rotating gobo, when its position is selected, the individual gobo can then be rotated and obviously it is possible to do combinations of either to give various types of effects (see Figure 11.3).

The units are used with a lighting console, using DMX512 control protocol. DMX 512 is an 8-bit system that allows for 256 discrete levels. When used for dimmers, this is more than adequate but when it is needed to control motorised lights, the resolution is not high enough, therefore more than one DMX is used to extend the system from an 8-bit to a 16-bit. In a 16-bit system, there are 65536 levels available, which gives more than adequate control for the fine movements on some of the lights. If the number of channels required exceeds more than 512, then it is possible to use another DMX link.

Figure 11.2 Mechanics of motorised luminaire (courtesy of High End Systems)

Figure 11.3 Optical system – motorised luminaire (courtesy High End Systems)

To give an example of a modern motorised effects light, we will look at the Studio Spot 575 made by High End Systems.

Studio Spot motors
Pan	One 3-phase stepper motor
Tilt	One 3-phase stepper motor
Shutters	Two 2-phase stepper motors
Colour	Two 2-phase stepper motors
Gobo select	Two 2-phase stepper motors
Gobo rotate	Two 2-phase stepper motors
Frost	One 2-phase stepper motor
Focus	One 2-phase stepper motor
Iris	One 2-phase stepper motor

The unit possesses a full colour mixing facility using two colour wheels (see Figure 11.4). All the colour settings are programmable and can be recalled from the controller's memory. The unit is convection cooled, thus there is no fan noise. It is fitted with 10 rotating gobos/effects via two six-position wheels. Remote focus is provided together with a shutter that can give instant blackout. All the functions are controlled by a 16-bit DMX512 and the functions include colour mixing, random gobo, gobo effects spins, variable frost, smooth mechanical dimming and a fade to black. The unit is fitted with a 575 W MSR discharge lamp.

Table 11.1 shows the colour combinations from the two wheels. The unit can be supplied with a 13°, 18° or 30° lens. The yoke fitted to the luminaire is capable of a 370° pan and 255° tilt, with an accuracy of 11.6 seconds (0.0032°).

Figure 11.4 Colour filter wheel (courtesy of High End Systems)

Table 11.1 High End Systems colour wheel combinations

Wheel 1	Wheel 2	Combination colour
Yellow	Cyan	Dark green
Yellow	Light cyan	Dark yellow green
Yellow	Indigo	Does not mix
Yellow	Pink	Orange
Yellow	Magenta	Red
CTO	Cyan	Moonlight blue
CTO	Light cyan	Blue green
CTO	Indigo	Dark indigo
CTO	Pink	Cherry rose
CTO	Magenta	Red rose
Aqua	Cyan	Primary green
Aqua	Light cyan	Indigo
Aqua	Indigo	Does not mix
Aqua	Pink	Does not mix
Aqua	Magenta	Does not mix
Pink	Cyan	Medium blue
Pink	Light cyan	Congo blue
Pink	Indigo	Indigo
Pink	Pink	Pink
Pink	Magenta	Broadway pink
Magenta	Cyan	Indigo
Magenta	Light cyan	Rose indigo
Magenta	Indigo	Indigo
Magenta	Pink	Broadway pink
Magenta	Magenta	Magenta

11.2 Digital projection

Most motorised lights rely upon changing gobos in the optical path and introducing coloured filters to get effects, but obviously those effects are limited by how many gobos and colour filters can be inserted into the optical train. If we look at some of the more complex drawing packages on the normal PC, such as the ones provided by Corel, we can form an incredible array of images and an almost infinite selection of colours. If we can now introduce that type of technology into motorised light sources, this would be an enormous step forward. In recent years, LCD digital projectors have taken over from the standard 35-mm projector used for video presentations, the advantage being that the output, usually from a laptop, can be fed to a video projector and hence onto a fairly large screen for presentations to a large group of people. During the 1990s Texas Instruments produced their Digital Light Processing system (DLPs), which has now taken over from LCDs, due to its superior structure. Digital Light Processing system works on the principle of a chip that is covered in minute mirrors, each mirror being one pixel, so for an 800 x600 resolution we have 480000 mirrors on a chip approximately 1 cm across. By tilting the mirrors, light can either go to the screen or not, and by introducing red, blue and green filters, for the primary colours, it is possible to produce an extremely wide range of colours. At the present time, projection systems which are adequate for projecting film in cinemas are now in use but unfortunately the light output would not be quite sufficient for effects in a TV studio. The LSD Icon is one of the first units that uses a DLP but at the present time, suffers from a low light output which will no doubt be overcome in the not too distant future. The advantage of this technology is that by using a simple DLP projection system which is controlled from a computer, any image in any colour can be rapidly programmed and presented. Even more importantly, to be able to do it in real time. Digital Light Processing systems have an advantage over LCD due to the fact the pixels are more closely packed than those of an LCD. Other than a much better resolution of images, the digital light mirror produces a brighter image. The digital light mirror chips have had extended life cycle tests, simulating 20 years of use. After these tests, no evidence was shown of any broken hinges on the mirrors in the devices. At the present time, the LSD Icon is the only integrated unit on the motorised light market, but no doubt all manufacturers are vigorously researching into this new development.

An interesting alternative development from High End Systems called VertiGo uses a standard video projector mounted in a motorised yoke. VertiGo is designed to utilise the versatility of video based image projection with all the finesse of control of a motorised light. All parameters of VertiGo are controllable from any standard DMX512 lighting desk in real time. The system offers total control of the lights position, its colour and shape of the projected beam. It is possible to provide shutters of any shape, irises of any shape and patterns derived from any standard picture or image file. VertiGo uses as its light source any standard video projector with smooth 360° movement through a twin periscope mirror head and software to manipulate any image through DMX512 protocol.

The VertiGo System consists of:

1. VertiGo periscope mirror head fitted to video projector,
2. rack containing control electronics for mirror head and DMX interface,
3. video effects computer and all image storage, and
4. connection to projector via standard SVGA or S video.

VertiGo operates with any standard video projector fitted with an SVGA input. High End Systems recommends using a 3-chip based projector for optimum operation.

The system provides:

• full colour playback,
• all control via standard DMX512,
• all effects are available in real time,
• still image or video from any source including live video,
• compatible with all standard image formats (MPEG, JPEG, QuickTime, BMP, TIFF etc.),
• instant selection of image from choice of thousands (Full David Hersey Associates and High End Systems gobo libraries included),
• rotation of image in all three planes,
• scaling of image in all three planes,
• full keystone correction,
• image pre-distortion onto any surface,
• image transparency,
• image trails,
• full anti-aliasing of image,
• overlaying of images,
• blending of images,
• colour mixing,
• graded colour (fountain fills),
• full pan and tilt movement, and
• control of projector zoom and focus where applicable.

When using video projectors we have to have some method of determining the light output and this is measured in ANSI lumens. This is ascertained by projecting an image 1 m² onto a screen, which is then divided into nine equal areas. Light is measured at the centre of each area and is then averaged. This is the brightness quoted for all digital and LCD projectors.

11.3 TV lighting

If we are using motorised lighting for TV, the larger luminaires used will always have barndoor systems fitted. Although some barndoors come with either four flaps, each with adjustable width of flap, or for that matter, eight independent flaps, we will examine the effect of mechanisation on a four-door system. Because barndoors are made with two small and two large flaps, the orientation of the doors allows oblong shapes at various rotational angles to be projected onto the sets. We must be able to regulate this rotation and it can be seen immediately that we will have to have some method by which the rotation is carefully governed so that we do not exceed a reasonable operating range and run into problems with control cable feeds, etc. Thus the rotation of the barndoor flaps is similar to that of the ‘pan’ system which allows for just over 360° of rotation. Each of the individual barndoor flaps has to be capable to being adjusted from fully open to fully closed and one of the problems with this would be that if two flaps are allowed to operate simultaneously, and they have to intermesh, there must be some safeguard so that they intermesh safely and do not cause mechanical jamming. This obviously requires a great deal of feedback from the angle of flap movement to the control system to compare the angle of each flap to ensure correct intermeshing. How far do we take the control of the barndoor system? Should we be able to rotate and adjust all four flaps at the same time? If so this probably poses bigger problems for the control system.

One of the biggest problems with having small motors attached to the flaps of barndoors, is that the barndoor system regulates the light beam, which unfortunately is one of the hottest parts of the luminaire, thus all the devices used on the doors have to be either carefully insulated or be in such a position that they are not affected too much by the light beam and hence heat. Having said that, the same would be true of any motors that are close to the body of a high powered light source in use, due to the radiant heat from the luminaire body.

In a manner similar to that of the ‘pan and tilt’ the repeatability of barndoor positioning must be obviously high. If for instance, a set of barndoors were used to project an oblong shape on a doorway within a film or TV set, the accuracy of that type of positioning needs to be extremely high.

Any luminaires used in TV and film would invariably have to be supplied to go with rigging systems and the whole has to be integrated very carefully. In TV one luminaire without lateral movement will not be able to take the place of three other luminaires. One of the problems in TV and film is that we've always got an obtrusive object called a boom microphone that hovers around creating rather nasty shadows if the lighting is not correctly positioned; therefore the position of the luminaire is extremely critical. In TV the control of the lights is relatively easy because the LD will have camera preview monitors to see the effect of any adjustments made, however in the film industry, this might not be the case although some systems do use combined video/film techniques. The biggest snag in the TV and film industry is the fact that the units would probably be too noisy for the quiet conditions demanded by the realisation team in any studio.

11.4 System control

We have talked at great length about the luminaires but somehow all their functions have to be controlled from a console of some description. It's more than likely that the console we use will bear a great similarity to a lighting control system and in many cases, the two are integrated as one unit. With more functions requiring control, the system has to be more complex which brings us to the point of how do the control signals go from the console to the functional parts on the luminaires? Well, we turn to our friend the ‘digit’ which rapidly goes down pieces of wire from the control area to the luminaires themselves. If the control system used means that a luminaire has to wait until another luminaire has finished all its functional movements, then this is much slower than a system which allows two or more luminaires to be adjusted simultaneously. The limiting point in the speed of operation is that, as more functions are required, each luminaire needs more control signals. These take a finite time to be accepted and made operable. If a large number of adjustments are having to be made at the same time, the system itself may become slow and cumbersome. Thus, the effects are observable and not acceptable as far as the LD is concerned.

Having decided that we require to get signals from point A to point B to control the luminaires, how are these distributed in the premises? It's impractical to take an individual feed to each luminaire therefore a superior way is to provide a digital control ‘bus’ such as DMX512 with provision made for take off points for the luminaires involved. This then means that each luminaire plugged into the ‘bus’ has to have a code number which is recognised by the control system itself. If any luminaire is changed within the lighting rig due to possible failure or a requirement change, a definite code has to be sent, on substitution, so that the system recognises the type of luminaire in use and its position in the system.

One of the reasons for using motorised systems is the requirement to reduce operating costs, and as can be imagined the cost of motorised lighting systems is fairly high. The cost of any system will be dictated by the complexity of the luminaires concerned: if simple functions such as ‘pan and tilt’ only are desired to be automated then this is obviously much cheaper than a TV studio full of multi-purpose luminaires where many functions would have to be controlled.

An interesting method of control from Whybron of America is the Auto-Pilot system. The system is designed to send signals through a system of luminaires so that the luminaires will track the performer as they move around on the stage. The Auto-Pilot system consists of a DMX compatible system controller, four belt packs and eight ceiling receivers. The system controller is connected between the lighting console and the automated lights. The controller receives DMX 512 data from the lighting console and passes along all the lighting parameters except the pan and tilt information to the luminaires. A performer wears a belt pack powered by a 9-V battery which sends signals to the receivers overhead. The system controller then uses this data to generate and insert the necessary pan and tilt information into the DMX data stream. As the artists move around, so is the pan and tilt information updated and thus the lights respond, following the performers’ every move. The system can accommodate up to four performers, using the same eight receiver array; the system is capable of controlling up to 24 lights simultaneously and it can be adjusted to suit performers of different heights.

11.5 Studio installations

Applying controlled mechanisation to the luminaires is not new and attempts were made in Europe during the 1970s to achieve some crude form of control. The units themselves were fairly cumbersome, utilising standard drive systems, such as small a.c. or d.c. motors.

What type of studio is suitable for a motorised lighting system? If we start at the lower end of the scale with small interview situations, there is probably no need to automate any small studio that has only two or three handed interview situations as the lighting could be left for the majority of the time and even when changes are desired, these would be small and relatively insignificant. Studios of this type often run with little or no electrical staff involved and in fact the lighting may be adjusted by any of the vision operators concerned. Moving up a notch, we get to a small studio of approximately 150m² which would be the type used for local programmes. In this type of studio the programmes are usually based around an anchor man/woman sitting at one position with two or three set-ups to cover for much of the news intake of the day and local current affairs programmes. They have, on occasions in the past, been used for small dramas and for small audience participation shows – all of which lead to variations in the lighting rig itself. Owing to the repertory nature and repeatability of the lighting over quite long periods, possibly over a programme period of 13/26/52 weeks, there is a definite need for a repeatable rigging system and an automated lighting control system in a studio such as this is highly desirable. The idea is that the LD could, in fact, have the studio rigged with about eight basic but different set-ups to cover most the situations he is likely to encounter on a day to day basis. Having received the information as to the programme content on a day to day basis, it would then be very easy for the LD to dial up ‘Set 1’, ‘Set 2’, etc. until he has the combination of sets so desired for the programme content of the day. If the luminaires are generally fixed in their application, such as a ‘key’ light, these will invariably be Fresnel spotlights, together with a requirement for softlights as fillers. However, to allow the LD a greater degree of flexibility, the use of multi-purpose luminaires is to be encouraged so that any luminaire can perform any function, within reason. Subsequently, there will probably be a reduction in the overall rig. This type of installation lends itself to the use of the motorised pantograph working within a reasonable range of lateral flexibility and height, together with a multi-purpose luminaire. This system, as already noted, allows space for luminaires to move alongside each other so accuracy of rigging is reasonable. It might be that the control system is clever enough to know if one luminaire is not within striking distance of another luminaire, it can move to a new position thus allowing accurate rigging. It may be an operational requirement that all luminaires are parked at one end of any trackway and the system should be intelligent enough to allow this operation to take place without any problems.

What happens when we go to a main line studio, say of about 500 m², where we would expect to cover any production such as drama, dance, music, light entertainment, audience participation, comedy shows, etc. If we take drama, it is quite possible that we will not necessarily be confined to single storey sets, but we may have multiple storey sets which causes problems because of their height. There could be scaffold arrangements built in studios of this type, which might be for high cameras, for example. It might be that we need special follow spot positions rigged which again involves scaffolding towers and special positions within the studio. There will be a need to light the cyc cloths to a higher degree of evenness than would be required in a smaller studio and this would therefore require special cyc lights to be rigged at high level. There will also be a need in the largest studio for scenery to be suspended from the grid itself, this necessitates the use of spot winching systems, lines and supplementary barrels or drapes to be positioned; all of which conspire against the movement of luminaires along the grid system, thus traversing becomes extremely difficult. The problem can be eased in a monopole studio by restricting the lateral movement of the units themselves. If we're considering a barrel rigged studio the problem is not so acute because the basic barrel system allows spaces for the scenery suspension system. It is only where supplementary barrels have to be placed, possibly at right angles to normal, that there could be problems.

The major drawback to automation in studios of this size is the fact that the programmes are not repertory by nature and are usually ‘one offs’. A series of six situation comedy programmes will be different in their content on a weekly basis. It's no good pretending that although we have a ‘stock set’ every week, such as a police station in a series of programmes, that lighting within that set will stay the same, because it will vary according to the action within that area. Therefore ‘normal’ lighting does not exist. This highlights the main problem when trying to apply automated systems to large studios. The lighting is extremely varied, there are difficulties in moving the lights themselves and this also requires that on every individual programme the LD would have to re-programme all the lights in the studio, or most of the lights, on that production, even on the repetitive week to week series that may be shot in the studios. If the system could be made as sophisticated as possible the LD would have the pleasure of sitting at home with his computer, working out the lighting plot and then sending it down the modem to the studio centre to have it rigged automatically. The problem comes – when does it get rigged? We are certain the Scenery department will be most indignant while they are rigging to find that lights keep moving around. Do the Scenery department have to say to the lighting man's computer ‘We've finished, you can carry on now’?

Large studio productions rely for speed and efficiency upon scene and electrical crews largely integrating their work output so that time is reduced in the rig and pre-light session. If we have to have a situation where the lighting has to be allowed to reset itself to new positions, is this done before the sets are placed in position? Because this is not the normal way of doing things. At the present time, sets are rigged and the lights are dropped in to suit the action on the sets. What happens if the scenic designer has made a change or for that matter the sets have been placed off their marks in the studio. This actually happened to one of the authors where the whole studio had to be relit from scratch, due to a design mix up prior to the first day of rehearsals. Would the lighting man's computer know this? And when his luminaires position themselves, would they be able to ascertain this? Not without extremely good intelligence which would require enormous computer capacity with a very sophisticated feedback system from the luminaires.

It would seem therefore that there is a case for automation in the smaller to medium sized studio but its application to large production studios is probably a remote dream and will probably never be realised. Even if we could have equipment of the intelligence required to solve many of the problems, could we actually afford all this equipment. Would our capital costs be recovered by the savings on the operating costs? Possibly with some of the clever young accountants of today this might be the case; but we believe in actual practice this is unlikely. With regard to the larger studio, what is desired is a better degree of control of the luminaires to help the LD. Remote control of the functions on a key light would allow the LD to adjust the effect while sitting in the correct viewing position. This applies equally to all forms of entertainment lighting.

One of the aims of lighting systems automation is that the LD would be able to sit at his desk, hopefully at home, and via his computer, draw a lighting plot which will then be rigged automatically at the touch of a button. It would also be possible to store and replay lighting plots on a ‘repertory’ basis so that set rigs could be rapidly brought into use.

A TV studio using 100 motorised luminaires would have its installation costs quadrupled. The difference in costs from using normal luminaires, would have to be paid back over a reasonable period of time to keep the accountants happy. The labour saved may produce a reduction in operating costs, but we may be confronted with a higher maintenance cost. Based on the experience of lighting control systems, which these days are extremely robust, it is more than likely that the system will give little problem over a 10-year period. If the new luminaires are more complex than the luminaires they have replaced, they will obviously have to be taken out for longer periods of time for maintenance.

The standard luminaires used in the TV and film industry, although they have generally high power outputs, give very little trouble if relatively basic maintenance is performed annually. In the case of automated luminaires, this maintenance will have to be much more stringent. In discussing maintenance, we have to bear in mind that this is generally only required because of breakdowns. What actually happens if a fully automated luminaire breaks down? If it was replacing three luminaires, the loss would be most noticeable.

Finally, and most important of all, what happens when the systems malfunction and every cue is uncontrollable?

11.6 Grid system functions

Control of lighting breaks down into three distinct areas:

1. control of the intensity of luminaires and their on/off function in some combination,
2. the elevation and positioning of the luminaires themselves by motorised lifting systems, and
3. control of the directional properties of luminaires and further functions for effect such as iris, shutters and barndoors together with the control of the colour output.

First of all, what is the basic function we require if we apply mechanisation to a grid system? It would be nice to be able to control the hanging of any luminaire in three planes i.e. its attitude across and along the acting area, coupled with the height of the luminaire over the acting area. The control of height is very straightforward. When using motorised pantographs and motorised monopoles, control of direction in either the x or y co-ordinates of the studio is extremely easy as the unit will invariably only have to motor backwards and forwards along a fixed trackway consisting of either barrel or RSJ, or a ‘C’ section channel system. Movement in the other plane would be more difficult to accomplish although not impossible. When rigging a monopole, and its associated luminaire, the only problem that exists for the operators is to have a nominated position for the luminaire to be hung in the studio and also sufficient space to hang it in the position required. Motorised barrel systems require a slightly differing technique inasmuch as there is no individual control of any single luminaire except when using short barrels, other than by use of supplementary spring pantographs on the barrel unit.

The height of a motorised barrel unit is generally dictated by the LDs requirements. The luminaire on its associated trolley is then moved along the bar to a point as near as possible to the nominated position in the studio rig. As has already been stated, this is somewhat of a compromise in practice. Where a horizontal bar some 2.5 m long is raised and lowered in a studio, its position in relation to the scenery is extremely important and in fact, it might be impossible to put the bar at the desired position due to the height of intervening scenery.

Motorised pantographs pose similar positioning problems to the motorised monopole with one big distinction. Where necessary, monopoles can be removed from their associated trackways and either lifted out to another trackway or by using crossover point systems between trackways, be diverted to adjacent trackways. The motorised pantograph system is generally permanently installed to the trackways and is not normally rigged or derigged in practice.

If we motorise the elevation of monopoles, barrel winches or pantographs, the safety cut-out systems employed on them should guarantee not too many mishaps in operational use. The slack wire cut-out operates very rapidly on these devices when meeting an obstruction on their downward travel: however, when individual units are not fully loaded, the overload system may not trip even when starting to pick up inadvertently, a relatively large piece of scenery. This highlights one of the major problems with total mechanisation of winching systems in that dangers are always inherent with scenery flats and other obstructions in the acting area, which really do require human supervision to ensure no malfunction of the system.

It is obviously relatively easy to add a motor to allow a unit to traverse along its trackway, but what happens to the luminaire at the base of the lifting device? Does it know that a scenery flat is in the way or that a luminaire in the trackway is in the position which we've nominated for the new luminaire. At what speed will our nominated luminaire approach the fixed luminaires within the rig? If we are using barrel systems and to avoid problems, it might be that only one motorised traversing unit has to be fitted to each barrel. However, to cover the studio area adequately, we would have to provide a large number of short barrels all over the studio. If we extend this principle of restricting the movement of the traversing system, would it not be sensible to restrict the movement of the monopoles in their trackways and the motorised pantographs in theirs, so that they are only allowed to travel in ‘safe space’. It is strongly suspected that this would be operationally extremely undesirable.

Let's look a little closer at the individual systems themselves and the problems they may pose and primarily look at the barrel system.

Barrels which may be 2.4 m long or a shorter one at 1.2 m long are installed to give as much coverage as possible within the studio. The length of the bars dictates the actual operational flexibility of the system. The more short bars are obviously preferable to fewer long bars. The BBC, for instance, use systems where two luminaires are permanently rigged to 2.4 m bars and one luminaire is permanently rigged to a 1.2 m bar, but there is always the provision to add extra lights to any of the bars in use for special requirements within a production. How would we get over the problem of the peak demand of studios where we do not necessarily always require the largest number of luminaires to be permanently rigged.

This brings us to the point as to how do we set about rigging a studio with motorised luminaires which are attached to barrel units. Although the barrel unit only has the problem of finding its nominated height as dictated by the LD, the luminaires, if motorised, would have to pan and tilt to meet the requirements of the LD. Two problems exist with motor driven pan and tilt with luminaires on barrel systems used in this way. One, is to avoid a luminaire on panning around crashing into its neighbour; and secondly, if the starting torque is high, it is more than likely this would impart motion to the barrel unit itself which would probably react by swinging like a pendulum for some time during the rigging period. The problem comes when adjustments are made to the lights in the rehearsal period, where motion is totally undesirable and would be extremely annoying from the point of view of the LD and even more so from the programme director's viewpoint.

Barrel units always have a tendency for some motion generally caused by their position near the floor which involves relatively long wire rope drops from the grid level. This statement holds true for standard winches with motors at grid level or for self climbing winches with integral motors. Other problems exist with installing mechanised luminaires on barrel rigs. Firstly there is the cost of installing fully automated luminaires on the bars themselves and secondly, what functions are required and how are these units actually controlled? The existing barrel systems usually have a reasonably generous SWL but it is marginal when additional temporary equipment is rigged. The additional loads presented by the motorised units may prohibit some types of temporary equipment being used.

The BBC have installed studios, varying from 140 m² to 220 m², with motorised pantograph systems. The reasons for their introduction are twofold: one of which is that they are much safer than the traditional spring pantographs used in small studios and secondly, if they are motorised for elevation and track position, they can be controlled from a remote point by one man, relatively easily. The basic premise of the original system installed was that if each motorised pantograph unit was fitted with a multi-purpose luminaire, a man with a pole in one hand and a remote control unit in the other, could rig and adjust the lighting in the studio with consummate ease. This system, although mechanised, has no inherent positional memory provided and thus cannot be claimed to be an automated lighting system. Additionally, the luminaires chosen for use have no motorised functions and are standard multi-purpose units.

The pantograph trackways are spaced at intervals so that the luminaires can pass each other when moving along their associated trackways, generally, with the barndoors open. It is possible to obtain greater flexibility to have the trackways spaced at smaller intervals but the barndoors may have to be closed when units pass each other. It is also possible to lower the luminaire to the floor so that its supporting pantograph, which is smaller in cross section, can pass between adjacent luminaires. Grids, in this type of studio are approximately 6 m above floor level, thus extra long pantograph units are not necessarily required. The pantograph only needs to reach 1 m above floor level so that luminaires can be rigged and derigged with ease. The signals coming from the control system, could be in many forms, but in the BBC were chosen to be a.c. mains signals, so that the amount of control gear built within any pantograph unit was kept to a minimum, thus reducing the possibility of operational failure. The electrical signals required for any unit is the ‘up/down’ function and for the ‘traverse’ function. In the event of control system failure, it was felt necessary to provide a pole operated control switch on the pantograph unit that could, by injecting mains signals, replace the incoming control signals and allow for local control of up/down and traverse motion. To avoid damage to adjacent units, buffers were fitted to the trolley units at the top of the pantograph rather in the style of an elongated version of buffers as fitted to railway locomotives. It is important that the traversing speed is not too high, so that the units themselves do not swing when in a lowered condition. To this end, all the pantographs have to be fitted with pivoting mechanisms at high level to avoid damage.

If either of the motor units fail, this is a severe operational problem in practice and to that end, the unit should be relatively easy to move off the trackway if the need arises. They would be rather unwieldy for the operational personnel to manhandle without safety problems being encountered, so this operation will probably require the use of a small local winch unit to raise and lower the old and new pantograph units into position. In practice, however, this type of unit has proved to be extremely reliable.

As the units are fitted with one luminaire, only one 5kW supply cable and socket for lighting power is needed at the base of each pantograph unit. The controlling a.c. mains feeds together with the lighting power, are fed to the motor unit at high level by a catenary cable system rather like those used with overhead electrical cranes.

At the moment it sounds as though we're discussing one unit in the track, which of course in practice is not the case, and more than likely six motorised pantograph units will be used in each trackway. If we assume three units would be fed by catenary cables from each side of the studio, then some degree of flexibility has to be inbuilt to the cabling system. It has to be noted that to reduce the amount of trackways for the cable systems, bunches of cable are suspended from either one or two trackways. These trackways are adjacent to their respective pantographs and carry one set of triple cables from one side of the studio and another triple set from the other. The flexibility requires that all the units have to be able to be positioned anywhere along the trackway, the only limitation being the space taken up by adjacent units. To achieve this means that the cables themselves have to be sufficiently long to allow any unit to reach its maximum towards the other side of the studio, allowing for parked luminaires, and that the cable between each unit also has to be long enough (say 8 m) to allow precise positioning of the luminaire.

The operator in charge of the rigging is provided with a small hand held controller. This controller, although it could be connected by flexible cable back to a wall termination point, is much better for use if it is not constrained by a length of cable. The hand held unit which could be infrared, rather like the controller for TV/video systems, but generally is radio controlled, the reason for this being that some problems have occurred in practice when using infrared systems and their reception, usually occasioned by flats and cloths and other devices being in the way in the studio area. The intensity of lighting itself however, has proved little or no problem for IR systems in the studios and experiments did take place where receptor units were exposed to the light of a fully spotted 5 kW luminaire and still were able to distinguish the infrared signals being received.

The small hand held controller is used to select the luminaire required in the studio and its associated pantograph and controls the luminaires ‘on/off’ function. It also enables the control of the ‘up/down’ and ‘traversing’ motion of the pantograph unit while the channel is selected. It is possible that, having selected the channel to be ‘on’ or ‘off’, to leave it in either state so that all the lights on any one area can be controlled easily. Initially, it was felt desirable to control the mechanical functions of only one unit at a time, thus avoiding any dangerous situations, such as a unit being moved inadvertently out of the operators’ eyeline. It would be possible, however, to control more units if it is assumed that the operator has a clear view of all units selected.

If radio control is used in an area, it is essential that the control unit is not operated outside of that area as the signals will be received by the base station and this would mean that the units in the studio would be controlled by somebody having no idea of what was happening. In practice this is overcome by ensuring that only trained operators use the system and they have strict instructions that under no circumstances is the controller to be used outside the studio. To prevent malpractice, the operators have to input an access code to the system.

Upon completion of the rigging period, the studio control system is switched off and the normal lighting control console takes over control of the luminaires themselves. The actual rig is now in position and unless small adjustments are required is left unattended.

The biggest advantage of the motorised pantograph unit is the fact that springs are not required, thus the unit itself is not load dependent. Any luminaire from the smallest to the largest allowed on the unit may be rigged and derigged in absolute safety.

We now come to studios which are utilising motorised monopole units for mechanisation. One of the problems with monopoles, as has been noted elsewhere in this book, is the problem that to move them around requires personnel working at grid level, possibly above artists and other personnel during rehearsals. In recent times, with the advent of stricter safety legislation, this practice has had to be tightened up considerably and quite often people are moved away from the area in which monopoles are being rigged and derigged, for safety reasons. It would be difficult to move the monopoles in their x and y axes without very complicated mechanical arrangements being made and it is preferable that they only traverse along sections of trackway. It would be desirable to limit that movement to certain sections of trackway, due to the need to avoid one unit hitting another or the possibility of fouling other pieces of studio equipment. If we limit the traversing of units to a specific distance, what distance should be involved? Probably, as a guide, it could be similar to that of the barrels on barrel winches, and therefore approximately 1.5 m. Monopole studios are usually constructed with trackways that are very close to each other to enable luminaires to be positioned almost anywhere. If we have a system where traversing is allowed even over short distances, we have to make allowances for luminaires to pass each other for overlap purposes and this would dictate the spacing of the trackways and invariably make them wider spaced. By doing this, we have negated one of the great advantages of monopole rigs, the fact that luminaires can be positioned anywhere. If we follow this argument to its logical conclusion, it would seem more acceptable to rig monopoles incapable of traverse in a standard monopole grid and only use ‘up and down’ motors on the units themselves. Having done this, we have taken away another advantage of monopole systems, the fact that rigging still has to take place to a considerable degree, requiring a reasonable number of electrical staff.

If we make the systems more efficient, it is the reduction of staff that is important from the point of view of cost saving. Rigging is the situation where the most staff are required, but any studio, once rigged, requires very few electricians to do the fine ‘trim’ that is desired by the LDs. If we automate a monopole rigged studio, what type of luminaires should be used? A motorised version of a multi-purpose luminaire seems to be the most logical choice. The ICARUS system is the first one introduced into general studio use that offers control of the luminaires and also suspension equipment. The controls are as follows: it is motor-ised trolley with point suspension (telescope pantograph or scenery hoist together with one fully automated luminaire); horizontal movement on the trackway; vertical movement of the suspension; luminaire pan, tilt and focus; barndoor rotation and barndoor positioning (see Figure 11.5).

Figure 11.5 lcarus system (courtesy of DeSisti (UK) Ltd)

The capacity of the ICARUS system, using self climbing or conventional winches, is for the control of up to 336 hoists each one equipped with three motorised luminaires giving a total of 1008 luminaires. There is no system limitation to the grouping arrangements, but it has to be borne in mind what would be the dynamic loads on the supporting grid system by the simultaneous movement of a large number of units.

The control console uses the standard PC using Windows programmes with appropriate graphics of the various modes selected and these are as follows: positioning luminaires – singly or in groups; the system also allows for live and preset settings. The various pre-set functions of the luminaires and winches or support systems can be memorised by simply giving it a file name and recording in the PC. The system also allows for hand held remote control units for setting up in the studio.

The trolley is driven by one motor drive wheel with a torque limiter which provides a degree of protection if the unit hits an object and comes to a stop. Feedback to the control system warns the operator and the software stops the motor after a few seconds. Information is input into the control system on installation which imposes a minimum distance between two or more moving trolleys, which is maintained even when they are moving. This is obviously necessary to prevent luminaires clashing.

The accuracy of trolley movement which is controlled by optical incremental encoders gives an accuracy of +/− 8 mm on 10 m of travel. The motors are equipped with soft start and soft stop functions to avoid any jerky movements. Telescopes are also equipped with optical incremental encoders for height information with an accuracy of +/− 8 mm on a 10-m extension.

The following table gives the conductors within the electrical track system. This works by sliding contacts on copper conductors similar to those used with overhead cranes, and the following figures are for 18 m of track. Each conductor rail is rated for 80 A.