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Lighting by design

The text below formed the basis for the article ‘Lighting by design’, published in Museum Practice journal number 6 in 1997.

Good lighting of a museum or gallery interior is vital. It can help the visitor to see well all the exhibits in the space in addition to appreciating the space itself. Poor lighting can make the space feel gloomy, the exhibits look unappealing and leave the visitor feeling let down or frustrated. Poor lighting can also leave the exhibits at risk from fading from excessive light or at risk of physical damage from visitors’ clumsiness caused by there being too little light or by glaring lights.

With the new museum of Islamic art we have the opportunity to light the architecture to bring out its grandeur and feeling of space and openness as well as the works of art displayed within it. Each work of art has been individually collected and so deserves individual consideration in its lighting. We would intend to work with the museum designers and staff to create a favourable lighting space for each object within the framework discussed below and within normal conservation, interpretation and display criteria.

Balancing act

Successful lighting of a museum or gallery is a question of balance. Balancing the needs of the visitors to see the objects well against the conservation needs of the objects; balancing the initial investment cost of the lighting and its controls against the running costs of the installation; balancing the various qualities of light available, the direction and the intensity of the light to bring out the best in an object and its surroundings.

Choosing the point of balance for each of these considerations will vary from gallery to gallery; from exhibit to exhibit and from setting to setting. The choice of lighting level is often the starting point for the lighting design. The section on conservation limits below shows that the light level for each object needs to vary depending on its susceptibility to fading or colour change by lights, although even here the values are not absolutes, but guides to be considered in balance with other issues.

Each room itself will impose certain restraints on the designers. Height and shape affect the sight lines from the lights to the objects and the ease of access for re-lamping and aiming. The position of side windows or roof lights impose an additional discipline on lighting levels and the positioning of objects to avoid reflections. Access for control or maintenance of blinds again affect positioning of both lighting equipment and exhibits.

Even where there are restrictions on the initial capital budget for lighting the long-term operating costs of the lighting systems must be considered. A cheap scheme now may lead to long term drains on the running costs of the building leading to repeated under investment in future. Trying to put into place the right quality of infrastructure for the lighting should be a high priority.

An eye for an object

It is often forgotten that the purpose of lighting in museums and galleries is for the public and others to view the exhibits on display. In some major international museums it appears that lighting has been provided solely to provide light for the cleaners or to stop people bumping into the exhibits. The best museum or gallery lighting prioritises the visibility and appreciation of the exhibits first and the room secondly.

From studies at University College, London and elsewhere, there is evidence of a benefit to be had from increasing lighting levels on works of art up to a point above which there is little reported improvement in viewing quality for increases in illumination. These studies found that raising the lighting level in a typical gallery environment to about 200 Lux was very worthwhile, but raising it much over 300 Lux did not seem beneficial. Obviously the type of object and the quality and colour of backgrounds will all affect this balance figure, but it is likely that for most gallery and museum interiors providing the visitor with 200 to 300 Lux on the art works would more than satisfy their needs in most cases.

As noted below, lighting levels need to be controlled to varying degrees for most museum exhibits for very good conservation reasons. There always needs to be a balance struck between lighting levels for good viewing and the conservation needs of the exhibits. It is often possible to play off one against the other. In a collection of drawings where only a small part is displayed at any one time, the lighting level could quite legitimately be raised, since the individual exhibit spends much of its time in store in darkness and thus the total light exposure will stay within overall recommended exposure limits. Alternately, the opportunity could be taken to still limit the light exposure on the objects to standard levels thus reducing even further the total light exposure on the object and hence reducing future conservation costs.

Adaptation and room appearance

It is almost always necessary to consider visual adaptation of the visitors eye to the various lighting levels encountered when visiting a gallery or museum. The first and greatest adaptation step to be handled is that from the outside, where the lighting level can easily be 50 to 100,000 Lux on a bright day, to the interior of the building. Here the secret is to delay the visitors in an intermediate lighting level within the entrance halls or lobbies before they enter the main exhibition rooms. This is almost always naturally achieved whilst the visitors are held in the entrance area for security checks, depositing bags in cloakrooms and obtaining gallery plans. During the day, if there is insufficient daylight entering the outer halls or lobbies, then lighting levels of some 500 to 1000 Lux should be provided on the surrounding wall surfaces, especially those with signs and displays. Lighting levels of the spaces the visitor passes through as they approach the galleries should be reduced further, especially if the visitor is about to enter a room lit to 50 Lux.

It is important to consider the overall balance of the light in each exhibition room, as this greatly affects a visitor’s opinion of the visibility of objects and the feeling of lightness or gloom. The lighting of the ceilings and upper wall surfaces are very important for the best appreciation of the splendour of the rooms. This can be difficult during daylight hours if there are side windows which tend to put more light on the floor and lower wall surfaces, leaving the upper walls and ceiling in relative darkness.

Conservation limits

It is well known that light, along with other environmental factors, affects the rate of fading and decay of certain materials. When these materials are used in works of art then the fading or decay can lead to changes in appearance of the work and to possible loss of detail or quality. From a conservators point of view as little light exposure as possible is what should be aimed for. From the point of view of those exhibiting the works of art, more light should be provided for the full appreciation and enjoyment of the works. For those objects relatively insensitive to light both of these objectives can be met, but for those object sensitive to light a compromise must be struck.

Most of the early work on light exposure and damage was carried out in the UK at the National Gallery in London. From this work recommended maximum illumination levels were given for various categories of object or material. This work has been continued and refined by many conservation and scientific staff at universities and galleries around the world. Although recommendations vary slightly from country to country there is broad agreement on what is the most appropriate compromise between conservation and appreciation of works of art.

For items that are very sensitive to light the illumination generally recommended is 50 Lux. For items of moderate sensitivity the limit rises to 200 Lux. There are also limits expressed for the amount of Ultra Violet (UV) light contained in the light falling on the objects, as this causes the most damage to most types of material. This limit, of 75µW/lumen, is usually met by using appropriate UV filtration on all window glass and by using tungsten or UV reduced tungsten-halogen lamps or using UV filters on fluorescent lights.

The maximum illuminance figures given above assume that the objects are in normal museum situation where the objects are exposed to light for about 3,000 hours a year. This equates to a museum opening all day for perhaps five or six days a week, all year round. As this is not always the case the limits are now more commonly expressed as a recommended maximum exposure to light during a year and this is expressed in Lux-hours, being the sum of the exposure in Lux and the duration in hours.

For very sensitive items such as most textiles and water-colours the annual limit is 150,000 Lux-hours.

For moderately sensitive items such as most oil paintings, wood and lacquer the limit is 600,000 Lux-hours.

For objects insensitive to light, such as most ceramics, the light level will only be limited by the need to keep within reasonable adaptation limits with surrounding objects. Thus, close to objects lit near to 200 Lux the lighting level on objects should not exceed 500 Lux. Where there are objects lit to about 50 Lux then no object near by should be lit above 200 Lux.

Flexibility

When considering a new lighting system it is often difficult to strike the right balance between flexibility and cost. Obviously you need to make the system flexible enough to meet your present needs for the correct lighting of the exhibits and their setting, but future changes must also be allowed for. Where cost is of relatively little concern, it is possible to install additional connecting points or track sections to take additional lights at a future date. It is also possible to put in more dimmer channels than is necessary to cope with future changes and adaptation. But where capital cost has to be tightly controlled, important decisions need to be made about how future flexibility can best be provided.

With the lighting points themselves, a track system, where suitable, can provide a simple way to add in additional lighting if it becomes required. As long as the track and dimmer module power capacity is chosen correctly then it is possible to add lights or change fittings as required. Track systems with two, three or even four circuits are available that allow two or more dimming circuits to be taken to each area as well as a simple switched circuit for cleaning lighting or security lighting for after public hours.

To get the most out of any system it must be easily and safely accessible in order to allow quick adjustments if objects are moved and to allow failed lamps to be replaced without delay.

Blending hard and soft light

When considering the lighting of any individual object or group of objects it is important to first of all consider what characteristic you want to bring out and show to the viewers. It may be the weave of a tapestry, the bold colours of a ceramic, the shallow relief of a carving or the shape or form of a vase. Once you have established this you can start to considered what light source will give the required colour quality and to plan-out the best position for the lights. Whilst this process is relatively simple for individual large objects some compromises are always needed where there are groups of objects displayed together. The lighting of many diverse object types displayed in one space are likely to be lit by one lamp type to avoid distracting colour shifts about the room.

There needs to be a balance between soft light and directional light, both on individual objects and within the space as a whole. The provision of soft general light in the room with more directional light on the exhibit does, in general, give the most pleasing effect. Controlled daylight can often provide some or most of the soft lighting, with the electric lighting providing the directional emphasis on the objects them selves. Some individual objects may well warrant a special lighting treatment with sharp glancing light to bring up texture or lighting from behind to emphasize translucency or the silhouette of the object.

Where the greatest mistakes are often made is in the lighting of highly light fugitive material, such as manuscripts and water colours. The need for low lighting levels often leads to a sense of panic amongst some exhibition and lighting designers. It is not necessary to plunge the whole room into darkness or to exclude daylight from such an exhibition room. The ‘knee jerk’ reaction to put such exhibits into black rooms leads to a ‘black-hole’ effect where visitors have to find their way around the darkened room and stare into dimly lit cases. By correctly using adaptation spaces and gently balancing the lighting of the exhibits and the room, it is possible to exhibit such objects at, or even below, the low conservation levels whilst providing good visibility and still keeping the room looking good, the labels visible and interpretative information still legible.

Daylight isn’t free

Daylight is considered by some as a nuisance or an uncontrollable intrusion into an otherwise well disciplined lighting scheme. For many types of exhibits this is most unfortunate as daylight adds a variability and naturalness to most displays. It should be remembered that most of the objects displayed are likely to have been created in daylight and were usually intended for display by the artist or originator with some daylight present.

For many top-lit galleries the sunlight shading can be achieved by passive shading techniques rather than active moving blinds or louvres. This has the benefit of reduced installation and long term maintenance costs. Where the level of daylight is going to be allowed to swing over and below a set-point, with perhaps the electric lighting dimming in response, then again a fixed, or seasonally adjusted daylight shading system can be considered. If more control of the daylight is needed then some form of movable blind or louvre will need to be carefully considered.

Lighting rooms from side windows can be problematic as it means that the wall opposite the window is preferentially lit and objects within the room are predominantly lit from this side. Pictures and similar objects on the wall opposite the windows will suffer from veiling reflections from the windows when seen from most parts of the room. Those hung on the window wall are often difficult to see well as the viewer has to compete with the relatively bright light from the adjacent window.

It goes without saying that all window glass should be covered by UV film or incorporate a UV absorbing interlayer and that it should be regularly tested for deterioration. Where there are problems with the total amount of light entering from a given window during the year then the type of UV film that also incorporates a light neutral density filter can be used. These leave a view out looking relatively normal, the UV restricted as before and the daylight admission reduced for these windows.

It should not be forget that during any evening openings when there is little or no daylight, the rooms will be lit from the electric lighting alone. It is quite appropriate for the feel of a room to change at such times and the visitors will expect to see the ‘lights on’ at such times, as they would in their homes or places of work, but it must be ensured that the electric lighting alone can provide the desired quality of light in the space and on the exhibits. The lighting should also be consistent in feel from room to room.

Objects in cases

Showcases are in effect small rooms where the same principals of soft plus directional light can often apply. It is usually a mistake to accept just the standard lighting solution of the case manufacturers. This often consists of purely soft downlight from fluorescent lights above the case. Whilst top lighting can be appropriate for some objects, most benefit from some side lighting to emphasise the modelling or texture. The classic failure of top lit cases is where there are a number of glass shelves in the case with the top shelf objects over-lit and those on the shelves below rapidly fading into darkness cased by the shadowing of the objects on the shelves above.

Purpose-designed lighting for cases need not be expensive if considered at the time the cases are being designed. If the case structure is created in tandem with the lighting solution an economic and flexible solution can be arrived at. This often involves fibre-optic lighting which can be used on its own or combined with fluorescent lights providing the soft general light.

Designed for future use

Often the use and flexibility of the lighting and control systems are not explained fully when the building is finished. This means that the abilities of the lighting system is forgotten about or underestimated. It is always important to ensure that comprehensive maintenance manuals are produced and that thorough training is provided to maintenance, curatorial and exhibition staff on the most effective use of the lighting. It is important to ensure that a complete understanding of the dimmer control systems is had. Then not only can the best performance be got from the lighting, but changes and alterations can easily be accommodated as time goes by.

Spare lights and accessories should be provided so that lights can be added to existing track systems or accessories added to existing lights. This will allow staff to better tailor the beam spread and distribution of an individual light to improve the lighting of an object or to reduce glare from it.

A full and comprehensively indexed set of spare lamps must also be provided. This ensures that the right lamp type and wattage is used in each light. This ensures that the lighting quality and distribution does not suffer over time as the wrong lamps are substituted for failed lamps.

Conclusions

Good lighting is the difference between an exciting and invigorating gallery and a dull one; the difference between repeat visits and a one-off look round; the difference between a successful exhibition and a failure. At the new Museum of Islamic Art we intend to use good lighting to get the most out of atmosphere created by the grand architecture and to show each individual exhibit in the best possible way.

The lighting systems will be designed to be used and understood by the curatorial and maintenance staff so that the museum will look as good after ten years as on the day the designer first set up the lighting.

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