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Lighting & energy use

The text below was that submitted to Museum Practice Magazine for their article ‘Lighting & energy use’. It was published in Museum Practice, issue 14, spring 2000.

The appropriate use of energy in lighting museums and galleries

The title of this article was chosen carefully. The words ‘appropriate use in..’ were used rather than ‘minimising energy use in…’ or ‘energy saving in…’ for very sound reasons. All to often the call goes out from on high to ‘save energy’. This can be done fairly easily, but at what cost to the quality of the lighting?

Energy use is only one of a number of factors that goes to make up a balanced lighting system. The most important is that the correct amount and correct quality of light is provided for each area. Some areas have particular levels of light that have to be provided for safety or for task performance. In other areas the lighting sets the mood or creates the right viewing conditions for an exhibition or a shop display. Just saving energy for the sake of it can be a false economy if it makes displays look uninteresting or merchandise unappealing.

What lighting, and hence what energy usage, is appropriate depends on the area being considered. The spaces within museums and galleries can be broadly divided into exhibition areas, other public areas and non-public areas. What spaces are in each of these areas will depend on the size and type of institution. In even the smallest of museums or galleries there is typically toilets, cloakrooms and some form of reception or information desk for the public. Behind the scenes there will be some office accommodation and storage, however small. As the institution gets larger so the public spaces expand to include shops, cafés, lecture theatres and education rooms. The non-public areas similarly expand to include more offices, storage, conservation and staff rooms.

Behind the scenes

The backs of house areas offer perhaps the greatest scope for energy saving in many establishments. Often under-investment over the years has left them with older, less efficient lighting. In many cases not only is the lighting using far more energy than is necessary, but may also fall short of modern lighting or health and safety standards.

For offices areas the right quantity and quality of light needs to be provided at each workplace. There is extensive guidance to lighting of all sorts of office spaces contained in the CIBSE guide ‘Lighting for offices’(1). Where computers are in use there are additional health and safety requirements. The lighting of such spaces needs to provide a balanced visual environment and not cause undue reflections in the screens. More guidance is available in the CIBSE guide ‘The visual environment for display screen use’(2).

For most back of house areas that are in fairly constant use modern, high efficiency fluorescent lighting systems are usually the best and most economical forms of lighting. There are a large number of manufacturers of such lights and finding the styles and type of such lights that is suitable for each space is usually fairly straightforward. For areas that are in use occasionally small compact fluorescent or tungsten-halogen lighting may be more cost effective.

Selecting or retrofitting the right controls for each space can have a big impact on energy usage. Each cellular office or distinct area within a larger office should have individual switching installed for it. Where rooms are expected to be left empty for reasonably long periods they should have occupancy sensors connected to the lighting to turn them off after a set period.

Public areas

It is important that these areas are well lit as they often have commercial as well as functional requirements. A shop or café for instance should be inviting and lit in a way that encourages visitors to enter and then to linger. The most effective form of lighting here is often general fluorescent to give some background lighting with spotlighting of sales displays and other feature points. Tungsten-halogen or metal-halide lamps are the best choice for the spotlights. Such mundane areas as toilets and cloakrooms still deserve to be well lit to create a positive image of the institution. Low-energy compact fluorescent lights are normally the best option here.

The lighting control system needs to be carefully selected for each area. For areas such as shops and cafés the lighting is likely to be on for the entire opening hours. Switching should be provided to turn off any display and signage lighting after visitor hours. Areas that are not continually occupied, such as toilets and education rooms can have occupancy sensors connected to the lighting to turn most of them off after a set period.

Exhibition areas

The exhibition areas in most museums and galleries are the most important spaces. They are the reason why most people come to the building and when they arrive they expect to be able to see clearly the exhibits. Saving energy in these spaces should not be a case of reducing the lighting level or the quality of lighting without due consideration.

The first step in any energy study should be to establish if the amount of light being provided in each gallery and case is in excess of the recommended conservation levels. If so there should be room to reduce the lighting levels. This must not be done at the expense of the lighting quality. In other words if the lighting levels in a case is excessive then simply removing one of a group of four spotlights in the case may result in the lighting being uneven. It is likely to be better to reduce the wattage of all the existing lights if possible or to look to more radical changes in the way the case is lit. The amount of expenditure justified would obviously depend on the extent of the over-lighting and the age and effectiveness of the existing equipment.

The next most useful step in day-lit spaces is to see if the electric lighting is on for unnecessary periods when there is sufficient daylight. Some care has to be taken here as for some exhibits electric lighting provides modelling light to bring out detail or texture on an object that would appear rather dull in just soft daylight. If it does appear that the electric lighting is on for excessive periods then the lighting control system needs to be looked at in some detail.

In judging the effect of differing energy using schemes it should be borne in mind that if the space is air-conditioning the running costs of the air-conditioning system will also decease if the heat load in the space decreases. In planning for a new scheme then a low planned lighting load can reduce the planned size and hence capital cost of the air-conditioning plant.

Lighting control in exhibition areas

The lighting in exhibition spaces should be divided up into zones relating to the fixed or relocatable structures within the space. This allows for different lighting levels or effects to be achieved in the different areas.

For both conservation and energy saving reasons low-energy fluorescent lighting can be provided for use out of hours. The control system can be set-up to provide a ‘visitor’ setting for normal opening hours and an ‘out-of-hours’ setting where all the cases and display lighting is turned off. This not only reduces unnecessary light exposure for the exhibits but also reduces the running costs for the gallery.

Display lighting on House lighting only on

[These photographs show the People’s History Museum in Manchester. We designed the system to light the banners and other displays to conservation levels during opening hours and for the display lights to go out and for low-energy lighting of the walkway areas to come on to during the closed periods.]

Cases

Showcases are often bought with the manufacturer’s standard lighting option already incorporated. This is often an array of standard fluorescent lamps above a louvre or diffusing panel. Whilst this option is cheap to buy and to run it is often not very flattering for the exhibits in the case. Some directional lighting within them enhances most case displays. This can be tungsten-halogen spotlights in the larger cases or fibre-optic lighting in smaller cases. Whilst adding this type of lighting to a case will cost more and will use more energy the display is likely to be enormously improved.

Exterior Lighting

The lighting of the outside of a museum or gallery can not only be a way of advertising its presence, but can also help to enhance the surrounding area. It is not necessary to light the whole of a building for the lighting to be effective. Special feature or details can be picked out, colour can be used for added emphasis or even moderate amounts of colour change or movement can be introduced.

The time that the lighting is on can be set for maximum impact with minimum energy use and running costs. Light cells or solar-dial time clocks can be used to bring lights on only when it is sufficiently dark for them to be most effective. The lights can be set to only come on during the weekends or just during the peak tourist season. Sometime bringing on special lighting for festival periods and other special occasions makes the building stand out more in people’s minds due to the surprise effect of the change.

Conclusions

Lighting is installed in a building for a purpose. If it is reduced or compromised for isolated ‘energy saving’ reasons it can compromise its original purpose. Careful design of any new lighting system or refurbishment of existing systems can lead to low running costs with good effective lighting. Good controls on both humble storeroom lights as well as main gallery lights can lead to worthwhile long-term energy savings.

An article like this can not hope to do more than bring the issues of appropriate energy use to the attention of the readers. For a more extensive coverage reference should be made to the excellent book by what was the Museums and Gallery Commission.(3). There is also a free guide published by BRECSU entitled ‘Introduction to energy efficiency in museums, galleries, libraries and churches’(4).

For a full coverage of the lighting of all parts of museums galleries and historic house the reader should refer to the CIBSE lighting guide ‘Lighting for museums and art galleries’(5).

References:

1. ‘Lighting for offices’. CIBSE Lighting Guide 7

2. ‘The visual environment for display screen use’ CIBSE Lighting Guide 3

3. ‘Museums Environment Energy’ The council for museums archives and libraries, 1994.

4. ‘Introduction to energy efficiency in museums, galleries, libraries and churches’. BRECSU, 1994

5. ‘Lighting for museums and art galleries’. CIBSE Lighting Guide 8.

CIBSE can be contacted on 0208 675 5211. BRECSU can be contacted on 01923 664258.

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