Lighting art to its best advantage has come a long way from the days of those dinky over-the-picture wall sconces. The principles that make retail merchandise pop and sizzle can be applied in our own homes, provided we modify them to suit the special needs of our more permanent collections.
Light draws attention to artwork but it can also put sensitive materials at risk of fading or other damage.
Effective display lighting has two components: general light and accent light. Accent light captures our attention by its intensity in retail situations up to five times brighter than general lighting. Retailers however, are in the enviable position of not having to worry about the long term effects of light damage. Still, museums, galleries and knowledgeable collectors can modify standard lighting design practices to suit the needs of their more fragile displays. Before we can talk about tweeking though, we need to understand a couple of lighting terms: Correlated Colour Temperature (CCT) and intensity:
CCT: The higher the temperature the bluer the light; the lower the temperature the redder the light. Northern blue light is in the range of 9000 degrees Kelvin, summer sun 5500 K, cool white fluorescent 4200 K, tungsten halogen 3000 K, incandescent tungsten 2500 K and candle light 1500 K. High temperature blue light has higher energy than low temperature yellow/orange light (its wavelength is close to ultraviolet ) and can fade and damage fragile artworks faster than low temperature light.
Intensity, the illuminance that reaches the object being viewed, is measured in footcandles (imperial system) or lux (metric system). One footcandle equals about 10 lux. A general feel for what lux actually describes can be gained by comparing the light levels recommended for certain tasks. The general lighting in a lobby might be anywhere from 20 to 200 lux. High contrast tasks, such as reading a typed page, can be comfortably performed for short periods at 200-500 lux. Low contrast tasks, such as reading mechanical drawings, would require 1000-2000 lux.
Museum guidelines recommend that very light sensitive media and materials such as watercolours, colour photographs, oil paintings with dyed glazes and silk, be displayed for limited periods at 50 lux. Oil paintings, on the other hand, are usually exhibited at 200 lux. Light impervious materials like stone or ceramics can be exhibited under much more intense conditions.
But how do we know what colour temperature and intensity to use? If artists create their work using high energy north light, shouldnt it be exhibited under similar light? Happily, high light levels and temperatures arent necessary to show art to best advantage. Research into visual psychology and museum lighting shows that the human eye is very good at compensating for lower light levels. In fact, the lower the light intensity, the better things look in lower temperature light. Experiments show that paintings exhibited at 200 lux look best at 3700 degrees Kelvin. Fragile pieces, that should be displayed under lower intensities, will look their best when lit with incandescent lights such as tungsten halogen or standard tungsten.
If general lighting is kept at the lower levels of lobby lighting, for example, 20-100 lux, accent lights can still create a dramatic impact at 50-200 lux. The requirements of the art determine the optimum light intensity, which in turn determines the optimum light temperature.
In the real world it may not be possible to keep to precise museum standards, but by understanding the general principles of lighting design and how the human eye sees under different light intensities and temperatures, we can take steps to display our collections to the best and safest advantage. Light sensitive pieces can be grouped together and shown in the less public (dimmer) areas, and highlighted with low energy accent light only when we actually want to show them off. Public areas with more robust artworks can be modified with drapes and dimmers to keep the light levels down when we are not using them.
Understanding the language of light, basic lighting design and visual psychology, allows us to communicate clearly to lighting designers and lighting retailers, so that we get lamps and results that best suit and best protect our collections.