13

Working lights and emergency systems

Introduction

In any area used for entertainment, there will be a requirement for four types of lighting:

1. Lighting for performance.
2. Lighting for working practices when the performance lights are not in use.
3. Lights provided for the benefit of audiences.
4. In the event of failure of the performance lighting, the working lights or the house lighting, an emergency lighting system has to be provided.

Houselights and working lights tend to describe lighting systems that may be achieving a somewhat similar result. In theatres, we would describe houselights as those used to illuminate the auditorium for the benefit of the audience. Working lights are used in the more technically orientated areas of the installation. In TV and film studios, houselights describe the fittings provided in a studio for general illumination and they are also the working lights.

When not using the performance lighting, we need to be able to see to work on rigging sets and to make changes to the production lighting within a building. In the so called ‘good old days’ this seemed to be answered, if one views any Hollywood movie, with a 60W lamp stuck in a stand in the centre of a stage. Unfortunately, in this day and age, that's not good enough, because with the advent of measures to increase safety within working premises used for entertainment, light levels have to be sufficiently high so that hazards to staff and artists are avoided. There are no hard and fast rules for light levels for working lights and it is generally left for the users to decide what is best for their installation. Guidance for light levels in various areas is usually given by the Code of Practice issued by various authorities for the country concerned.

13.1 Types of sources

Before we discuss where to put working lights in any premises, perhaps it would be a good idea to review the light sources available, their advantages and disadvantages.

For many years, tungsten lamps have been used for house lighting and working lights and there really is not much of a problem when using this type of source. By choosing the correct lamp it is possible to get a reasonable light level commensurate with a reasonably long life. It is helpful if lamps don't have to be changed too frequently, because they are invariably in slightly inaccessible positions. The main snag with tungsten lamps is that their efficiency is low and they produce quite large amounts of waste heat. In film and TV studio installations a considerable amount of power can be used for the house and working lights and in fact, in some studios, this might be as high as 30 or 40 kW.

It would seem advantageous, therefore, to go to other sources of light and first of these would be the fluorescent lamp. Fluorescent lamps, which are more efficient, generate much less waste heat, which is advantageous from both the electrical and air conditioning viewpoints. One of the problems however, of fluorescent lamps, is that unless used close to the working area they provide broad sources of illumination and are not as convenient as focused down lights which may be required when the working area has a high grid. It would seem fairly obvious that we might be able to employ high bay lighting, such as in factories, using mercury discharge lights. The advantage of this type of lighting is that it is more efficient with much less wastage of power. But, mercury discharge lights have one major drawback – they take time to reach full light output; and if they fail whilst they are burning – and thus are hot – they take a long time to cool down. This means a long wait before the lamps can be restruck.

In the past, the BBC experimented with the use of discharge lighting for houselights in a studio at Television Centre in London. The installation made use of reasonable quality mercury discharge lamps in parabolic reflectors aimed down to the studio floor area.

To get around the problem of the warm up time of a discharge lamp, a tungsten lamp was positioned adjacent to each of the discharge sources. Upon initial ‘switch-on’ the tungsten light was activated as well as the discharge lamp; after about 10 minutes; the tungsten lamp was extinguished because, by this time, the discharge lamps had reached their stable working condition. In normal use, if the supply to the discharge sources was interrupted, either by the operators switching ‘off’ the working lights, or by failure of the incoming mains, the tungsten lamps were re-activated and the control circuits waited for the discharge lights to cool down for a set period of time before re-applying their ignition pulses. This required a reasonable amount of intelligence to be built into the control system for the studio, particularly as the working lights were split into four quadrants and each was treated independently.

Several facts emerged from this experimental installation, one of which was the lamps used did not maintain a good colour over their operational life and therefore some distortion was caused in the colour rendering of materials and drawings in use, being particularly troublesome to the lighting and scene crews involved. There was also a reasonably high degree of flicker present from the discharge sources. The periods of changeover from tungsten to discharge were annoying in practice and the operators much preferred the tungsten light, although it had a slightly lower light intensity. Finally, but not least, the installation of the system incurred high capital costs and although it was felt that these would be recovered in a reasonable period of time, this was not the case in practice.

A major operational problem nowadays is the need to have an emergency switch to isolate the production lighting in the event of any electrical hazard occurring in the working area. When the main production lighting is removed, the working lights need to be activated immediately, and discharge sources take too long to come up to full light output.

Having looked at the light output of sources used for working lights, what about the colour? We find tungsten lights will invariably give good colour rendition and cause very few problems in practice. If we choose to use fluorescent tubes for lighting the working area we have to be careful in the choice of tube so that the colour rendition is of a high order. Modern discharge sources can now be obtained with very good colour rendition and greater stability throughout their working life. In all cases it is important to avoid strobing and flicker.

For TV and film studios (working/houselights) a light level of between 200 and 400 lux is generally acceptable: but it should be borne in mind that when it is lower than this, the working conditions can become hazardous.

13.2 Integrating the system

Having decided upon the type of light source that we will use for a working light, where will we provide it? In the theatre, the main areas will be in the wings, above the grid, on the fly galleries and a general illumination on the stage itself. In all these areas a reasonably high illumination is required so that the operators can see clearly what they are doing, thus avoiding any accidents when handling scenery, luminaires and counterweight sets. Other than the working lights in any area, there is also a need to have some level of lighting backstage during the performance. This is to enable the stage operatives to react to cues and thus perform lighting and scene changes. It's fairly obvious that this shouldn't disrupt the performance lighting on the stage itself and thus interfere with the effect intended by the LD. This background lighting must be of a sufficiently high level so that it too avoids any safety problems.

All of this activity is occasioned by the ‘live’ performance. In TV and film this is not the case! Having set up the scene, movement is then restricted to keep background noise to a minimum while the scene is recorded on either film or via TV cameras. Thus, the need in TV and film studios is for working lights over the whole area to enable sets to be erected, dressed and lit and then ultimately used for production shooting, when the working lights will be switched off. In film and TV, if there is a need for some special working lights within a production area, due, for example, to quick change dressing room facilities being required, localised lighting is usually provided.

In the larger TV and film studios fluorescent lights are not generally used, tungsten sources being preferred and these are usually in the form of long life 1000W linear lamps mounted in floodlight fittings pointing downwards or in the general direction of the acting area. This enables a reasonably high illumination level in the main area. In smaller studios, it is quite possible to use fluorescent fittings to provide an adequate light level on the studio floor. However, it may require several twin units to produce the light level required as it is more difficult to provide focused beams with fluorescent lamps as a source. One of the problems of mounting any form of working light in a grid system is the fact that there are so many objects hanging from the grid, obscuring the working light. In a large studio, we get the crazy situation when all the winches are raised towards the grid level, we have unobstructed lighting of the studio floor, but when we lower the winches to their operational height, which would be the main requirement when rigging and setting, the working lights are obscured.

When illuminating the acting area it's bad enough trying to position a small floodlight fitting about 300 mm square within a grid system, but when trying to install fluorescent fittings up to 2 m in length, it's almost impossible. Small lighting units can be installed between the ends of barrel winch units and not interfere with the main production lighting layout. Fluorescent fittings, however, can only be positioned between rows of production lighting units and this, of course, in practice means valuable space is occupied.

Other than the fittings below the grid level which illuminate the main area, there is also a requirement to illuminate above the grid for operators working at that level, although these lights will only be used occasionally and not permanently switched on.

In large studios there is a provision for some emergency lighting that is left alight all the time, usually fed from a central battery power supply. This has to be carefully integrated with the rest of the system, although the light level provided is low in comparison to the main house lighting and therefore generally does not affect the production lighting.

We've now got lights all over the place! How do we switch them on and off, because it's pretty obvious that switching them all off at the same time may be inconvenient and possibly dangerous. Most studios have the lights switched in four quadrants, thus it is possible to have a quarter of the working lights on, with three quarters off and this switching arrangement can be in any combination for convenience. One big problem with a high light level from the working lights in a studio is the fact they are also a major source of illumination and can project quite obtrusive, unwanted shadows. So although the lighting can be removed in certain segments, it is usually necessary to switch off most of the working lights during a production so that any undesired effects are avoided.

It is necessary to have an emergency ‘off’ button which operates the main lighting power. This is provided to remove the power from the active area in the event of fire or any electrical hazard. The application of this switch, which removes the main lighting, could plunge the area into darkness and so that this does not happen, an interlock system has to be provided so that when the production lighting is switched ‘off’, the working lights are immediately switched ‘on’, thus avoiding any danger. The emergency ‘off’ buttons operate on a latching system and therefore are not allowed to be reset until an authorised person investigates the problem and clears the situation for normal operation again.

Whatever type of lights we choose for our working lights, there will be a need to maintain them. This might be simply changing a lamp when it fails or cleaning the fittings on a regular basis to ensure maximum light output. This requirement means we have to carefully consider where we put the fittings and how they are accessed in normal use. Obviously in a small studio, using tungsten or fluorescent fittings, a pair of steps or a reasonably short ladder may be used by operators to gain access. In premises where high grids are installed, there will be a need to provide access to the working lights, generally from the grid system itself to avoid the use of high portable towers. On occasions there will be a need to lower the fittings to the floor and this requires lifting devices to be installed for every lighting unit.

Tungsten working lights and house light systems usually have thyristor dimmers to control them. Some modern studio installations have sophisticated control systems in an attempt to save power. The method of control is to generally have a period when the lights are fully on which is usually worked out from normal rigging practices and this amounts to say, 4 hours. At this point the lights will slowly fade down to half brightness, thus saving some energy. If the operators are still working and require the higher light level, the action of touching the ‘on’ button of the system, re-activates the circuits to maximum and a further 4 hour cycle commences.

On all types of working lights where there is a lamp involved we obviously have to take safety precautions. It is rather unnerving to have a lamp explode above members of staff or the public. Having only a mesh in front of any of these working luminaires is insufficient, and it is essential that no material escapes from one of these fittings when it is above people. In the case of tungsten or discharge fittings, it is possible to have safety glasses fitted which are toughened and in addition to the safety glass to also have a mesh to prevent pieces of the safety glass falling to the floor level. With fluorescent fittings, specially designed units can be obtained that are generally safe in most aspects. It goes without saying that all these fittings have to be fireproof!!

We have already mentioned that around the edge of a stage area there will have to be working lights left on to enable staff to perform some of the functions during a live performance. In TV particularly, there is a need for items of equipment to be illuminated around the edge of the studio for normal use, but which must not be too obtrusive when using the studio for recordings or transmissions.

Many TV studios are often fitted with cyclorama cloths that at times can encompass 2/3 of the periphery of a studio and this can pose a problem inasmuch that direct access towards an exit doorway is not possible, and an alternative route has to be available. There are strict rules concerning how much of a studio can be encompassed by pieces of cloth or sets and there must be definite access ways provided for safety. A problem that often occurs in TV studios is that the exit lights have to be left on and if a cyclorama cloth is hung across the face of the exit light the camera will see the outline of the ‘exit’ sign through the cloth, thus the exit sign has to be obscured in some way. The safest method, by far, in these circumstances is to hang some form of material in front of the sign but this must be hung as near to the cyc cloth as possible, so that the normal sight line to the ‘exit’ from the fire lane at the rear of the cyc, is maintained.

Additionally, around the edge of the studio there will be consoles for local control of the winches, pantographs, monopoles, together with controls for switching lights on and off. All of these need illumination for the operators to see what they are doing, and this is generally accomplished by having fluorescent downlighters mounted above the panels which can be obscured from the view of the camera. Unfortunately at times the outline of the panels can be seen through cyc cloths and therefore local switching arrangements have to be provided so that the fluorescent units can be switched off if the camera is looking in that direction. A fire lane will invariably be provided all the way round the edge of the studio and to ensure that illumination is sufficient for rapid access in the case of an emergency, fluorescent lights are provided at frequent intervals, attached to the studio walls. These also require baffles so that the cameras cannot see this illumination.

In a theatre, there will be permanent arrangements for an audience, this being part of the normal operation. However, in film and TV studios, audiences are not the ‘norm’. When they are there, it is essential that the safety arrangements made are as good as those in theatres. Special arrangements have to be made to indicate clearly the exit routes; although in most modern studios the audience seating is generally integrated into the building, so there are definite access routes. If, however, the audience seating is placed in the area on an ‘ad hoc’ basis, then special arrangements have to be made. This is particularly important with regard to the lighting. In the event of an emergency it is essential that the audience is safely conveyed away from the technical area being used for the production, which is the high risk area. Thus special temporary lighting arrangements have to be made to light the exit routes, particularly around the audience rostra.

13.3 Lighting in control areas and dressing rooms

Although not usually of direct concern to technical consultants planning lighting systems, they should be aware of the requirements for control rooms and dressing rooms. In the control room used by the LD, there will be a need for downlighters onto the desk adjacent to the lighting console so that they can interpret the prepared lighting plot for the production in question. It may be that they have used colour coded symbols to indicate cyc lighting colours, for instance; therefore, in addition to a reasonable light level, there is also a requirement to have faithful colour rendition. In TV, the LD is intimately involved with the technical picture quality from the cameras and therefore has to use high grade monitors; in good viewing conditions, which implies almost dark surroundings. The only areas of light will be those on the control desk. Desk lighting these days is usually achieved by having fluorescent fittings to give a general background illumination along the working edge of the desk, with small tungsten spotlights to pick out areas of special interest. Both the fluorescent and tungsten lighting have to be provided with dimmers so that a balanced working light level is achieved.

Traditionally, dressing rooms are lit by banks of tungsten lamps around a make-up mirror. In recent times, however, fluorescent lighting has been used in an attempt to give a more even illumination which is kinder on the performers’ eyes and also helps to save energy. The most important aspect is that the fluorescent tubes chosen must be a very good quality from the point of view of colour rendition.

This latter fact also applies to the fluorescent tubes used over control desks.

13.4 Emergency systems

Emergency lighting can take two forms:

1 ‘Standby lighting’ Where essential work is allowed to continue (this would obviously be more applicable to a hospital operating theatre). In general in the entertainment industry, standby lighting is not normally installed. It may be provided on occasions in those areas concerned with TV master transmission suites which have generators backing the public electrical supply systems, feeding the technical plant, so that a minimum ‘on air’ presence is maintained.

2 Escape lighting This is required in areas occupied by staff, artists and audiences so that a rapid, but controlled, exit can be made from an entertainment area in the event of fire. It is the most important form of emergency lighting as its main requirement is to ultimately save life.

The essential requirement for emergency lighting is that it will operate reliably from an independent source other than the mains supply. The light level required for safety lighting is remarkably low and in fact for most areas a level of one lux is considered sufficient. However, the light level is really up to the installers and operators of the premises to review, and if necessary, increase upon this base level. Other important purposes of emergency lighting are:

1. It must clearly define the exits and all the emergency exits.
2. All escape routes must be clearly indicated and adequately lit so that people can see their way to exits.
3. It is essential that the lighting along escape routes is relatively even and does not have wide variations in light level.
4. It is absolutely essential that, having got out of the building, all the people evacuated don't blunder into pitch blackness, therefore outside illumination must be provided.

One of the most onerous requirements of emergency lighting is the fact that it has to reach the desired light level within 5seconds of failure of the main lighting system. It is possible that the response time of the emergency system can be increased up to 15 seconds with the permission of the local authority, providing people in the building concerned are very familiar with their surroundings. However, in most cases it's preferable if the 5 seconds is maintained. Due to the 5 second limitation, it would obviously be impossible to use discharge sources for emergency lighting, and in fact the only types of lamps preferred for emergency lighting are from the tungsten and fluorescent families.

It is also extremely difficult to use a generator for the emergency lighting system due to the fact that they, also, need a finite time to run up and in most cases will probably exceed the 5 second limit. The main source of supply for emergency lighting is a battery system, this can be either a central system where the emergency power is distributed to the areas concerned, or self contained systems where each individual luminaire used comes complete with its own battery. In the past many large installations used large banks of batteries contained within a battery room in the premises to provide d.c. voltage to the emergency lighting systems. In essence, the battery system works rather like the battery on a car; in normal use, any drain on the battery systems by maintained exit signs or maintained house lights would be catered for by a charging plant in the same manner that the alternator on a car keeps a battery topped up. With failure of the mains, the batteries are always in a state to provide an emergency power source for a reasonable period of time. Battery powered emergency lighting is usually designed to be activated for a period of up to 3 hours, according to the size of the premises and with due regard to all the problems of escape from the building.

Battery backed luminaires used for emergency systems are usually reliant upon the normal mains input to provide a trickle charge so that the batteries are maintained in a working condition at all times. Luminaires for emergency systems come in three types:

1. The first of these is where a lamp is ‘off’ until any emergency arises, in which case the lamp will be powered from the internal battery pack. Normally the mains feeding the unit will trickle charge the battery pack.
2. The second type of unit is where the lamp is always in use and under normal circumstances powered from the mains, but in an emergency situation will use the internal battery supply. Once again, the incoming mains trickle charges the battery.
3. It is possible to combine the two types of operation in a third sort of luminaire for emergency systems, and this luminaire contains two lamps; one which is used normally, powered from the mains and a second lamp for use only in emergency conditions, powered from the internal battery pack. In the event of mains failure the second lamp will switch on. As before the unit relies upon a trickle charge from the normal mains to keep the batteries in good condition.

A problem that arises with emergency lighting luminaires is that if the lamp in the fitting is used all the time it is in a constant process of ageing, hence some notice must be taken of its life cycle so that lamps are changed to avoid failure in emergency conditions. Units that employ lamps which are only switched on in emergency conditions need to have these lamps checked at fairly frequent intervals to ensure no possible malfunction when used. It is also extremely important that all units installed in the premises are switched onto the emergency state at fairly frequent intervals to ensure that the batteries are working correctly.

In the entertainment industry the members of staff working in the premises will be aware of the escape routes, exits and emergency exits. Unfortunately, members of the public may come into these premises and will be totally unfamiliar with the layout of the building. This requires that the operators of any premises have to ensure that all exits, be they permanent or temporary, have to be clearly marked. As well as the need to have clear exit signs and lighting for the emergency routes, there is a need for additional lighting where hazards may exist along a route, such as stairways and any other type of obstruction. Obviously these must be clearly lit so that no additional problems are caused by people tripping over obstacles. It goes without saying that, if in doubt, put more emergency lighting in.