James White

Museum lighting is in a period of revolution, and lighting designers are facing fundamental changes in their design decisions. This is a result of the International Commission on Illumination's (CIE) publication “Control of Damage to Museum Objects by Optical Radiation,” CIE 157:2004 that shifts the focus of the illumination of artworks from illumination levels to total exposure over time. It also reassesses energy use in museums in line with concerns about climate change. Designers are being encouraged to look at new technologies, largely in the form of LED sources, and to address methods of lighting control.

The challenges created by CIE 157:2004 relate to reducing light exposure of objects not solely by illuminance levels but by also paying attention to the duration of exposure. The responsibility to manage this does not rest entirely with lighting designers. It requires curators and conservators to take a more proactive role, and to accept that any exposure to light causes deterioration in light-sensitive materials. Therefore, when and how long an object is exhibited determines the survival of the object more than the specific light levels to which the artwork is exposed. CIE's publication also implicitly challenges the extremely high levels of light used by conservators during condition assessments and at other times when an artwork is in their charge. Light exposure during this time should also be accounted for in the overall history of the object.

Lighting controls are becoming an essential tool for conservation and they provide significant energy savings. In museums, lighting designers are setting up control systems that turn lights on and off as visitors walk through galleries. The challenge is to create a system that works seamlessly: The museumgoer should be largely unaware that a control system is in place, except for when the lighting is a part of the artwork or the display technique. Depending on the setup of the exhibit, visitors can be given the ability to control the light in specific cases or displays, or lighting can direct the visitor by using dynamic lighting of specific displays or elements of an object.

One critical component in this equation is the light source itself. As the industry shifts from using incandescent to solid-state sources, the question remains: What are designers being offered as replacements for low-voltage lamps?

Solid-state lighting can no longer really be considered a new or emerging technology. LEDs have been in use for architectural lighting applications for more than a decade, and LEDs and fixtures that use them continue to be plagued with excessive claims about their life span, efficiency, and output. Although there are now standards that describe how LEDs and LED products should be measured, such as LM-79 and LM-80, these standards do not inform designers about the reliability of the products. They only provide a basis under which they should be tested and how claims and specifications should be made.

So how are changes in the technology of light sources affecting conservation requirements and how artworks should be lit? What do designers need to consider when assessing LEDs for museum lighting applications?

The first thing to remember is that LEDs are not a like-for-like swap with low-voltage tungsten halogen, no matter what product literature might indicate. There are many replacement LED lamps on the market, but they are not ready for museum applications. The U.S. Department of Energy has been doing excellent work through its CALiPER testing program to evaluate products, and offers designers guidance for luminaire selections.

Ultimately, it is not possible to achieve the same performance as low-voltage tungsten halogen lamps by using LEDs when they are packed into the space of an MR16 reflector lamp. Compromises are required in thermal performance that lead to lower light output, lower efficiency, and shorter life.