It is very important to have confidence in the material categories and its characteristics for all the materials to be displayed. This means that all materials, including colourants and varnishes, have been correctly identified, and that their responsiveness has been correctly classified, and only a professional conservator has the skill to do this reliably. The conservator’s decisions may cause difficulties for the lighting designer. For example, it may become necessary to set up a controlled daylight gallery as a restricted exposure location, to enable all the responsive materials to be appropriately displayed. The earlier in the process that these issues can be discussed with the exhibitions designer, the better.
Enough has been said in the foregoing pages to make it clear that there is a lot more to lighting than providing prescribed illuminance values. Ambient illumination, and whether or not spaces are daylit, strongly influence display lighting options. The extent to which appreciation of the displayed objects depends on recognition of form or texture, or on discrimination of detail or colour, or of transparency or lustre, demand careful consideration. Do the objects have glossy surface characteristics, and if so, is this to be revealed, as for polished wood or glazed porcelain, or not, as for a glazed picture or a glossy photograph? All of these factors are the concerns of the lighting designer, and no matter how experienced that person may be, setting up, aiming and adjusting the lighting is a time-consuming process that must not be rushed. It is necessary that the important visual attributes of the objects are effectively revealed.
The illuminance levels for responsive materials require careful consideration. A lighting designer who starts from the standpoint that the aim is to reveal effectively the visual attributes of the displayed objects with minimum incident light, quickly discovers that some objects need more light than others. Furthermore, this need can be affected by changing the surroundings. Background lightness and colour are influential in ways that depend on the material being displayed. Sometimes a strong contrast is effective, as when clear glassware is displayed on a dark background, and in other situations it is beneficial to minimize contrast. Watercolour paintings tend to benefit from being displayed on a background that matches them closely for overall lightness and colour tone. Generally, paintings appear darkened when hung on a light-coloured surface, and a similar darkening occurs when there is glare, direct or reflected, in the field of view. By overcoming such darkening effects, there may be opportunity to reduce incident light, and this approach contributes both to visibility and to conservation.