2

Lighting the subject

From the time when the Savoy Theatre, London, was first lit by electricity in 1881, the instruments used for artificial lighting have developed from very crude flood sources to the sophisticated moving light sources of today.

Early light sources were generally floodlights with little or no finesse. As taste became more refined, so did the lighting. The majority of lighting is placed at a reasonable height above the acting area. The reasons for this are quite simply that we do not wish the acting area to be full of equipment. This holds true for most lighting equipment, but in a TV or film studio the floor is also cluttered with cameras and booms, etc. As members of the human race we are conditioned that light is above us and at an average of about 45° to any standing object on earth. This fact lays down the most important ground rule for the artificial lighting of any scene. Artists throughout the ages have appreciated the light sources available to them. The sun provides a wonderful key light with warm rich colours and the blue sky provides a softlight of cool brilliance.

The subject may be either a performer or a static object and the lights have to be positioned and controlled to give the desired effect. Sometimes, compromise is necessary due to the position of scenery, cloths, and other objects which may give rise to unwanted shadows. The choice of luminaires for the lighting designer is extremely wide and varied, but all will have their particular favourites because they know that they can produce acceptable and repeatable results from some of the devices used in the past. Lighting designers these days can use lights from another branch of the industry to give some effects that were previously unobtainable.

To the untrained eye, lighting, either in the theatre, TV studio, on a film set or in a huge ‘Pop rig’ looks somewhat similar. However, closer inspection reveals that the luminaires used in the theatre are somewhat different to those used for film and TV and these days will probably have more in common with the ‘Pop’ industry. We find that stage lighting designers now use Parcans together with automated luminaires using tungsten and discharge sources. Many of the luminaires used on stage and for that matter in the pop world are now being used more and more in TV.

In our everyday lives as human beings, we go around in illumination that can vary from the minimum amount on a moonlight night to a maximum of an overhead sun in the Sahara desert. Other than a psychological difference, we are not disturbed by the differences between gloomy, grey overcast days and the intense blue skies of winter when the atmosphere is at its clearest. Visually, we are not worried by a lack of shadow detail, and on other occasions we see no problems with the intense black shadows created by sunlight. We do become disturbed however, by green light applied to the human skin, we also become rather unnerved by lighting when it comes from below subjects and not from above. In our everyday lives we are conditioned by the most basic form of lighting which consists of a reasonably well balanced mixture of sunlight and light from the blue sky.

In the absence of light from the sky, such as on the moon, we see extremely contrasting pictures due to one light source only, namely the sun. We feel much better when we are bathed in warm sunlight and not standing in the cool of a grey day. Some of this is caused by the generation of vitamins by sunlight, but mostly it is psychological. It is interesting to note that we also feel better on a sunny day in the middle of a cold winter. Red and yellow give us a cosy feeling, and this is probably occasioned by our mental stimulation with the association of the sun. It's a strange fact that as colour temperature increases towards the blue end of the spectrum, we do not necessarily feel warmer and we actually associate blue with cool conditions. Green has a refreshing quality, which is probably occasioned by the response of the eye which is at its peak with the green portion of the spectrum. We view black as a very sombre colour and associate it with the macabre. We generally associate white with coolness and a feeling of something that is quite unspoilt; it's interesting to note how disturbed we are by snow when it has become muddied, as the thaw sets in. From this short list of examples, it must become obvious that we can associate colours with a sense of stimulation of appreciation within the viewed scene, and many of the effects used in artificial lighting are based upon these feelings.

Light in its most basic form, daylight, consists of a mixture of sunlight and skylight. These can be analysed as the sun which provides extremely hard light that gives well defined shadows and a sense of depth; and the sky which gives very soft diffused lighting without any obvious shadows. The reasons that the light behaves in different ways is that the sun is a very small source in comparison to the subjects it illuminates, hence it produces the hard shadows, whereas the sky is an extremely large source in area and thus produces almost shadowless lighting. Note the term almost because no lighting is shadowless and if an object blocks some of the light rays it will produce a shadow, however diffuse!

‘Soft’ or ‘hard’ is a relative term. For instance, a softlight can give reasonably hard shadows, whereas a larger softlight positioned at the same distance, will produce a softer shadow. Conversely, a Fresnel lens luminaire with a brushed silk diffuser fitted can give quite a soft result when used close to the subject.

It must be remembered that both ‘hard’ and ‘soft’ light have the same physical properties. ‘Hard’ light consists of light rays going in straight lines from a very small source to the subject, whereas ‘soft’ light consists of the same light rays emerging from a larger source area going to the subject in straight lines from a variety of angles (see Chapter 6, Figure 6.18).

An important factor in the use of softlights, which is often forgotten, is that they have two planes of illumination, the horizontal and vertical. As the width of the softlight becomes greater, so the vertical shadows become more diffuse. When the height of the softlight is increased the horizontal shadows become more diffuse. Obviously, there is a finite size to softlights, but the most effective for many subjects are those that are reasonably wide in relation to their height.

We hear the term the ‘quality of light’ – all light is essentially the same, except for the colour. However, when we look at light from a carbon arc it appears to have a very hard, sharp, focused quality, whereas subjects lit by fluorescent lighting have a much softer look. The difference, on the surface, between a 150 A carbon arc with a Fresnel lens, and a4kW HMI with a Fresnel lens, is very slight. In practice the HMI appears to be a softer quality. These observations generally apply to hard light, whereas when we examine soft light, irrespective of the source, the results are always somewhat similar.

What constitutes good or bad lighting is very much the opinion of the observer, but there are certain ground rules which can define the quality of lighting as perceived by the viewer of the scene. A good example of bad lighting, when shooting film and TV material, is the incorrect colour of the light sources or choosing the wrong colour correction. The balance between modelling lights and fill lights has to be closely controlled or it may give problems with contrast and exposure and as well as creating ‘grainy’ or ‘noisy’ pictures. Highly saturated colours when used for TV give a very overpowering result due to the size of the screen image. Extremely steep lighting from above a person will give very distorted features on the face and for that matter if the lighting is from beneath (see Figure 2.1a and b). It is essential for film and TV to have a good contrast range within the scene to avoid a flat result. This is not to say that lighting has to obey a fixed set of rather boring rules but the choice of light sources, colour and special effects has to be carefully thought out and balanced against what is stimulating and what is annoying. The very best lighting for film and TV will be largely unnoticed by the viewer and, if this is the case, the lighting designers’ aims will have been achieved.

Figure 2.1 (a) Underlit; (b) Steep lighting

Most of the lighting conventions used in the film and TV industry emerged from the earlier days of film when all the material was shot in black and white. It was obviously extremely important to give a sense of depth to pictures and when one sees some of the original extremely old movies that were made without the use of enhanced artificial light, and shot purely by daylight, the results are somewhat flat and uninteresting. During the late 1920s and early 1930s increasing use was made of high powered light sources in the film industry and these enabled the lighting cameramen to achieve better results than previously. Hollywood discovered that a key light placed at the correct angle could enhance the artist greatly. Thus we had ‘Paramount’ lighting where a hard key light was fairly low and straight onto the face, which enhanced the beauty of ladies with high cheekbones, Marlene Deitrich being one supreme example. The film makers also learnt from portrait painters and noted that a more interesting result could be given when the key light was not straight to the face, but taken to the side and thus had a type of lighting known as ‘Rembrandt’ portraiture. Probably the pinnacle of black and white film lighting is that of Citizen Kane, with its highly dramatic portraiture and extremely imaginative use of shadows and highlights. The advent of colour film, with its lower contrast range meant that the lighting cameramen had to control the lights to a narrower band of illumination, using colour more imaginatively to obtain contrast.

Whereas the theatre and the concert arena have to be lit for the entire viewed scene, the film and TV industry is lit ‘piecemeal’. Television studios will often record material using several cameras which will require the scene being lit as a whole. Traditionally, the film industry has shot scenes using one camera position at any one time, therefore the lighting is only adjusted for that camera position. When the camera position is moved, the lighting is re-adjusted to suit the new position. This has two distinct advantages, one of which – you only need one camera and secondly – not too many lights. This technique is also used in TV these days, particularly on location. A problem that exists with this technique is that continuity has to be watched very carefully, thus sunlight, if not accurately noted, could vary in its direction within a room. Obviously, this is much more applicable to drama than it would be to, say, musicals which would have to be lit in their entirety, irrespective of the varying camera positions. Close-ups in TV and film means that there is a need for better lighting on the artists and parts of the setting. The mere fact that the close-up can dwell on an area for quite considerable periods of time, necessitates a greater attention to detail.

2.1 Basic lighting

We have to remember that luminaires work in three dimensional space, they can move in two directions in the horizontal plane and be adjusted vertically. Additionally, we are concerned with the direction of light, the texture of light, the colour of light and the intensity of light.

Whereas lighting for the theatre and a pop concert relies upon the skill of a Lighting designer visually balancing the intensity of light and colour, in the film and TV industry there is a requirement to achieve certain light levels, and an understanding of the problems with the factors that have an influence on incident light, is useful subject matter for this book. The floodlighting fraternity use horizontal plane measurements for their lighting. In the film and TV industry, we are concerned with vertical planes such as actors and sets. In general, most people know that light falls off with the square of the distance, however, many people are unaware that the angle of the incident light falling on the subject also has an effect on the light level which consequently influences the reflected light which stimulates our eye, the film stock and the CCDs in the TV camera.

Light in the vertical plane

Most measurements assume that the light is directly on axis and that, at a set distance from the source, the incident light level will be l/d². In the examples that follow, it will be seen that the angle of incidence (Cosine law) also affects the light level.

Figure 2.2 Incident light

Figure 2.3 Lighting the subject: Light in the vertical plane

Table 2.1

It will be noted that the differences in light level and incident angles are not very great except when close to the luminaire e.g. 2 and 3 m.

Throw

Cosine

Incident light level is given by:

Basic lighting has very similar fundamental requirements, and the main forms of illumination used are as follows (see Figure 2.4).

Key light

Why is it called the key? The luminaire used provides the principal light on the scene and tends to be the key to the whole picture. It establishes the mood and character and generally is capable of producing acceptable results when used on its own. However, it makes no contribution towards the depth of the picture. Key lights for film and TV tend to be used at a vertical angle of 30° to the subject but can be within the range of 20°–45°, although the lower angle can produce disturbing glare to the actors. The key light can be used over a horizontal angle of incidence within 45° either side of the normal to the subject. As a general rule 30° vertical and 30° horizontal displacement gives extremely satisfactory results for visual close-ups.

Back light

A back light is needed so that separation and depth are enhanced. The positioning of back lights is extremely critical and they should not be placed too steeply in the vertical plane because they may spill over onto the subject's face and create rather disturbing effects. Back lights can be varied much more than a key light for their angle of incidence and in fact many good effects are produced by taking them to extremes. The back light is usually around half the power of the key light, but if increased gives a much more dramatic effect. Single back lights can be effective on the subject but quite often twin back lights are to be advocated for any subject with long hair.

Fill light

Why do we require fill light? When viewed with the eye, a subject lit with a key and back light will look perfectly all right, however, due to the restrictive contrast ranges used for film and TV, the results would look somewhat over-contrasted when viewed either on the cinema screen or the TV screen; therefore fill light is used to reduce the contrast by diminishing the shadow areas. As a guide, the lighting level of the fill light is about 50% of that of the key. One point that should be noted is that having made a shadow with one light, there is no way that the shadow can be removed or diminished to any great degree by the addition of more and more fill light. Fill light is often a soft source because we are used to the sky being our fill light. However, if we use hard light in a controlled manner, which is a technique used by lighting designers, then we can still achieve a pleasing result. Whereas, in the theatre and at a concert, double shadows might not be quite so apparent on the human face, they are extremely apparent in close-up in the film and TV media.

Figure 2.4 (a) Soft fill at 45θ (b) Soft fill from side (c) Hard fill from side; (d) Twin back lights; (e) Keylight only (f) Cross keys; (g) Back lights and keylight; (h) Back lights and soft fill (i) Final lighting

2.2 Choice of light sources and luminaires

Due to the merging of techniques throughout the lighting industry, it is very difficult to decide what type of source would be used in any one particular branch of the industry. However, we can generalise and say that in the film and TV industries, Fresnel lens luminaires using both tungsten and discharge sources predominate. High efficiency PAR discharge sources are being used in both the TV and film industries. Television studios favour tungsten as the predominant source, as it is easy to control and produces extremely good lighting effects; whereas film and outside broadcasts are very big users of discharge lighting. More recently ‘low energy’ lighting has been introduced into smaller studios, in the form of fluorescent lighting. Although not giving such strong subject modelling, as the more focused sources would, it does allow control of output light level by dimmers with consistently good colour and with less heat.

All lighting requires to be fairly accurately positioned to give the correct effect that the lighting designer desires. The height of the lights is important in relation to the horizontal distance to the subject. In film and TV, flexibility in height and in the xy axis, along and across the studio, is given by the various types of suspension systems on offer. With fixed suspension systems such as a TV studio grid, or truss members in a rig, movement is generally achieved by pan and tilt, horizontal and vertical movement being very restricted. It is of course possible to provide local flexible suspension such as pantographs, which allow adjustment in the vertical plane. In TV and film, the size of the luminaires prevents close proximity working and the type of suspension systems often do not allow precise positioning in the horizontal plane. This is often circumvented by using cross bars, enabling lights to be positioned in a more precise way but often with a penalty of tying up two suspension points.

If we look in lighting manufacturers’ catalogues, we will see a variety of soft sources on offer, and these go from fairly large to small luminaires. Therefore, it would appear that the larger ones are softer than the smaller ones, and this of course is true if they are set from the subject at the same distance. However, the small soft near to the subject may provide a softer result than the larger one, at say, twice the distance. This is due to the apparent area of soft light at the distance, due to perspective, and of course, the same effect applies to hard sources. It should always be remembered that a softlight looked at full on, presents a large area source, but when viewed from the side, presents a very small source and this has often been the undoing of many a lighting designer in the TV industry. It's a wonderful way of producing unwanted microphone boom shadows!

In TV and film, because of the need for broad lighting techniques, luminaires with much softer edges are employed, therefore the Fresnel spotlight becomes more useful with its soft edge to the light beam which allows an integration of light sources for a much smoother result. In the film studio, a 2 kW Fresnel is a relatively low powered luminaire, 5 kW and 10 kW tungsten luminaires are more the norm. The need of the film industry for extremely high light levels, particularly when colour was introduced with the old Technicolor process, etc. necessitated high intensity carbon arc sources, culminating in huge things like the ‘Brute’ with a power of 225 A. The arcs were often used on location to balance the shadow areas in scenes lit by sunlight. The carbon arc was superseded by discharge luminaires using HMI and MSR lamps and there is much to commend these lighting sources, they provide a very high quality light output which is about four times greater than their tungsten counterparts. Unfortunately, they can only be dimmed to 50%, and thus do not allow for complex lighting effects changes.

In TV and film studios, the workhorse of the lighting director is the focusing Fresnel spot, whereas the same Lighting Director (LD) working outside on an OB or interview situation, will often use open faced luminaires. Normally, an LD who is given the choice will choose to work with the Fresnel spot because it offers many advantages over the open faced luminaire with a focal range from a 10° beam angle at spot to a 60° beam angle at full flood and a light output range of about 8:1. The light is very evenly distributed without striations in the beam and the barndoors provide a good soft edge cut off. The Fresnel luminaire, however, is most inefficient as a source with an efficiency of around 8% in spot and 26% in flood. When used in studios the lighting level from tungsten sources is quite acceptable because the cameras can be set to work at a much lower lighting level than is often possible on location where work is carried out in daylight and requires the artificial lighting to blend in with the high level of the ambient daylight and to match the same colour temperature. Interior shots on locations may be lit with either tungsten or discharge lighting and it may be necessary to work with daylight coming through the windows. When using tungsten, this problem can be solved by either placing an orange filter on the windows and balance for 3200 K, or balance for 5600 K and use a blue daylight correction filter in front of the luminaire which unfortunately reduces the light output to about 27% at the very time that a high output is required to try to match the daylight intensity. Another solution is to use discharge lighting which offers a high light level, blends exceptionally well with daylight and is cooler in operation, but is more expensive than tungsten and requires a control ballast.

The focusing open-faced luminaire, such as a 2 kW Blonde, has a much better efficiency than the Fresnel with up to five times more light in the spot mode; and nearly twice as much when in ‘flood’ compared to a 2 kW Fresnel. This variation in efficiency is due to the fact that in the ‘spot’ mode the lamp is relatively close to the reflector and the stray light is much reduced compared to the flood position. Redheads and Blondes are small, light and relatively inexpensive but the trade-off is a hard shadow produced from the direct light of the lamps’ filament, with a second shadow produced from the reflector which is superimposed over the first shadow, giving harsh shadows. Light spill can be a problem and the barndoors are not very effective. The typical focusing range for a Blonde is from a beam angle of 23° in spot to a beam angle of 70° in flood with a light output range of 8:1. The Redhead goes from 42° in spot to 86° in flood with an output range of 6:1.

The profile spotlight enables precise control of the beam, the size of which is controlled by an iris diaphragm. Profile spots are also fitted with metal shutters for producing hard flat edges to the beam, and special shapes can be introduced into the projector gate of a profile spot. The edge of the light beam can be made either fairly soft or very hard by adjusting the lens. Many modern profile spots in use have zoom optics which allow a great deal of flexibility when rigging and lighting in the areas concerned. The Parcan has a beam width dictated by the type of lamp used. With the correct choice of lamp and subsequently rotating the position of the lamp, it is possible to vary the beam shape quite successfully. It may also be advantageous to use a brushed silk filter in the luminaire to further modify the beam spread. Although the Parcan does not have the same flexibility as, say, a Fresnel spotlight or a profile spot, they do have advantages – they are cheap to purchase, fairly easy to maintain and allow a multiplicity of effects at not too high a cost.

Lighting in the film industry generally tends to be from the floor upwards. Because of the rehearse/shoot techniques of the film industry, a production is generally filmed shot by shot. To make more effective use of either studios or locations several scenes may be shot at the same time, but not necessarily in the order of the script and final print, and put together in the editing room. To make the lighting as flexible as possible, it is useful to have the luminaires mounted on adjustable stands which can be moved to new positions very quickly by the electricians on the set, rather than having the lights suspended from the ceiling which tends to be rather fixed and time consuming when changes are required. For the suspension of lighting units in film studios, the simplest form is to have a block and tackle with the capability of running along a steel RSJ mounted at roof level. Thus a single point suspension can be used which could be pulled across or along the studio. One drawback to this system is that to introduce any new light at any position often requires shifting other lights which causes further rigging problems. Another technique is to suspend long platforms with handrails either side, called ‘boats’, where several luminaires can be rigged on the rails and manipulated by electricians manually. Although access to the luminaires is obviously better, changing the position of the boats in the studio is a time consuming process, and probably only pays dividends when luminaires are set up for quite considerable periods of time on a major production.

Film lighting does not rely upon dimmers to balance the lights. Lighting intensity is adjusted by spotting and flooding luminaires, by the careful selection of the power output of luminaires and, if necessary, scrims and neutral density filters can be used to achieve technical balance. The main reason for this technique being used is that film stock is generally balanced for 3200 K or for 5600 K daylight. Although the film stock concerned will have some small latitude of colour response to the lights concerned, the film industry has always gone along with the fact that the lights should be relatively fixed in relation to the 3200 K or 5600 K standards. When filming, it is necessary that the majority of the luminaires will be either tungsten or discharge sources; if not, there will be a requirement to colour correct some of the various light sources. For many years, tungsten was the main source of most illumination in the film studios, with carbon arcs being used when higher power was required. Nowadays, discharge lighting is normally used, due to its greater efficiency and cooler operation.

2.3 Lighting systems

Television lighting, which evolved from film lighting, relied on the tried and tested methods used by the film makers for many years, and many of the original TV studios were, in fact, converted film studios. As TV became more and more sophisticated and the need for a greater productivity arose, the studios had to become more efficient with their output being raised so that the need for additional studios was avoided. During the 1960s it was possible that a day's filming would yield 2 minutes of finished material, whereas in TV the need was to produce 30 minutes from each day of production. The basic luminaires used in TV, after the Second World War, were the Fresnel spotlights in 1 kW, 2 kW, 5 kW and 10 kW versions together with a miscellany of softlights such as Scoops, Tenlites, Hewitt Banks, etc.

In Europe during the 1950s, tremendous strides were made in modernising TV studios; the greatest of these was the adoption of motorised rigging systems, such as the monopole and motorised barrel winch. This enabled a small team of electricians to service a studio rapidly and effectively and most important of all – safely. Subsequently the monopole system was generally employed where fairly accurate rigging was required, but not used on a saturated basis, working on the principle that lights could be moved to suit during the rigging periods. The solution reached by the BBC for monochrome TV during the 1960s, was to equip all its main production studios with motorised barrel winches utilising 2 kW Fresnel luminaires and Tenlites for soft sources.

The advent of colour saw a different technique evolve at the BBC. The single Fresnels and softlights were replaced with the multi-purpose luminaire which is a combination of a softlight and a hard light. This tends to be somewhat of a compromise as a soft source because of its small physical size and compact reflectors, but it was a fairly good Fresnel spotlight. By having the complete area covered with the multi-purpose units, a saturated lighting system was evolved where the need to rig and de-rig luminaires was avoided, and the BBC achieved extremely high productivity in its studios, based at that time on multi-camera shooting techniques. The multipurpose luminaires were generally fitted with a twin 2.5 kW lamp in the Fresnel half and four 1250 W linear lamps in the soft half. This allowed the luminaires to be either in a 2.5 kW mode, or a 5 kW mode and enabled the operators to control the light level and colour temperature over various distances of ‘throw’ within the studio. A later development provided one filament at 1.25 kW with the other at 2.5 kW, thus enabling a range of one third, two thirds or full power, giving a much better control of light intensity within the limits of colour temperature, with the soft end of the luminaire fitted with 4 × 625 W lamps capable of being switched between 1.25 kW and 2.5 kW only.

With the spread of colour TV in the United Kindom experiments took place to ascertain the parameters that could be used to maintain good colour balance for the pictures, but allowing some form of control on the lighting itself, and it was found that a tolerance of 200 K either side of 3000 K was reasonable; thus the cameras were lined up for this colour of incident light. The light level requirement was given by the sensitivity of the colour cameras working between f2.8 and f4.0. The dimmers used in TV studios normally have a square law light output, which means that the square of the fader setting from 1 to 10 gives the percentage light output, i.e. level 6 = 36%. It is normal when commencing operations in the studio to align the channel controllers to position ‘7’ which means that the dimmer would supply current to operate the lamp at 49% of its light output; its colour temperature at this point is approximately 3000 K. As we have an acceptable variation of ±200 K, it allows the fader lever to go down to ‘5’ with a 25% light output and when faded up to ‘full’, to have 100% light output; thus we have 2 stops (4:1) variation in the light level. This system allows a wide variation in the intensity of light and allows a great deal of control so that we may balance the light sources. However, it requires that all luminaires are fed from dimmers; thus there is a need for large dimmer installations.

When using discharge lighting at 5600 K the tolerance is generally accepted to be ±400 K.

In both the film and TV industries, if the key light is between 30° and 45° in the vertical angle to the subject, the luminaires height above the studio floor will be dictated by the power output of any luminaire used and the intensity of light required on the subject; e.g. a low powered luminaire will be positioned closer to the subject and consequently will be lower in height to maintain the same incident angle. In TV this approximates to around 4 m above floor level. In the film studio it may be that the height above the floor is increased by using higher powered luminaires. In all branches of entertainment lighting the luminaire positions are greatly affected by their relationship to the scenery. On some occasions it will be impossible to get the preferred light source high enough and it may be necessary to use a smaller luminaire closer to the subject. On other occasions large pieces of scenery, as found on the opera stage or the double storey building on the film set, may force the luminaires to be unnaturally high, creating a requirement for much more powerful luminaires. Due to the decrease in lighting levels required in TV studios, we have seen the introduction of 3 kW lamps to replace 5 kW lamps in 5 kW luminaires with a light output in the same ratio as the kilowatts i.e. 5:3.

Generally in TV studios, there is no problem with large variations in light levels as they are well controlled within the studio area. On outside broadcasts, it is a vastly different situation where the light level may vary from almost nothing to light levels as high as 120000 lux. There are occasions, however, where the controlled conditions of the studio and variations in light level of the outside world have to come together, and these are usually in studios where windows are provided to give a natural backing. Although neutral density filters can be used on the windows it will also be necessary to raise the interior light level so that there is some approximation to the incoming daylight. However, this usually results in some form of discomfort glare to the artists and the generation of heat, caused by the high light levels. In these cases, of course, one invariably resorts to discharge lighting with its much more efficient light output. An important factor when designing for studios such as this, is the direction of the light through the windows. It's rather unfortunate if you are facing south west in the northern hemisphere and getting the rays of the dying sun. One method that was used at the BBC to control the incident light from the outside world was to use Polaroid sheet applied to the windows, with a rotating Polaroid filter in front of the studio camera. The rotational Polaroid only caused a 50% reduction in the reflected light from the subject to camera. However, the combination of the rotating and fixed Polaroid allowed the windows to be controlled from 50% transmission down to virtually 0% transmission. With the addition of an electronic exposure sensing circuit it was possible to have the rotating Polaroid filter automatically adjust according to the incident daylight. This method is only useful if the window has small areas of glass, as Polaroid sheet is only obtainable in fairly small sizes. Incidentally, the luminaire employed as the frontal key was a 1.2 kW Fresnel spot discharge source in ‘flood’.

Temporary TV studios overlooking sporting events may require several levels of lighting being used to match the daylight, and it may be that the daylight keylights are 4 kW Fresnel discharge sources in full spot to give sufficient light level, whereas the night time lighting may be down to quite small discharge sources such as the 575 W in full flood. The natural light will vary in relation to the artificial light; but by using a selection of luminaires with various power outputs and switching between them it is possible to balance for the incident daylight. Of course, it is possible to balance for the maximum incident light level and just let the background slowly diminish over a period of time but with presenters using prompters and the danger of a high glare factor it is preferable to adjust the lighting to create more comfortable conditions. As the natural light diminishes changes are made between the various sources and it is hoped that these go relatively unnoticed by the viewer.

When filming for slow motion, the camera has to operate at a high shutter speed so that when played back at normal speed it produces a slow motion replay. By increasing the frames per second rate means that every time the frame rate is doubled from normal, i.e. from 50 frames to 100, we would have to double the light level to produce the same exposure effect. High speed video and filming is required in industrial research applications. Frame rates may be anything from 1000 to 10000fps. When filming at rates of 1000 and 2000 frames, light levels of 120000 lux are necessary and to put this in perspective normal sunlight level is around 130000 lux. It is obviously possible to produce high light levels using many tungsten sources but this has a heating effect which does not help with experiments. The most efficient way of producing the very high light levels required is to use discharge lighting. Due to the fact that discharge lighting is approximately four times more efficient than tungsten, a 1 kW HMI unit will be 4 times brighter than a 1 kW tungsten unit. It is possible to increase the light output of a double ended HMI lamp by doubling the current through the lamp for a very short period of time, therefore a 4kW HMI lamp can be boosted to 8kW for periods up to 20 seconds, more than enough for usual high speed video cameras. The ballasts have to be flicker free to provide a steady light output at high shutter speeds.

Light sources and luminaires come in a variety of shapes and sizes and whether tungsten, discharge, fluorescent or any other type of lighting is used, the final result will depend upon the intensity, colour, quality of light and incident angle to the subject. Lights are only a means to an end and even the most modern lighting devices will not correct for bad lighting practices.

To put the whole subject in perspective a famous British lighting director once said of one of his colleagues ‘that man could obtain good pictures using candles mounted in milk bottles ’.