Many institutions need help in identifying what level of light an object (art, artefact, manuscript or book) should receive when exhibiting, either in their own displays or on loan. Many objects will fade over time if displayed regularly and there is a measured level of fading, called the 'Just Noticeable Fade', that has been defined based on an object's sensitivity to light. Given the wide range of materials that can be displayed, with different types having different sensitivities, is can be hard to know how long to exhibit an object. Most collections exist to be seen and popular objects are inevitably placed on display more often than others.
So how does a custodian decide what level of light and how long and often should an object be displayed before it risks fading? Can we decide that, given the demand for popular items, we can accept as a policy that a small level of just perceivable fading over a very long period of time will happen? If so, what time is acceptable? 10 years? 50 years? 100 years? There is much information available about light fading in standards such as BS 4971:2017 or guides such as PAS 197:2012, offering information about what types of material fall into what sensitivity category: High, Medium or Low. None guides the custodian to identify the policy decisions they should make in such a way that they can translate this into amounts of light exposure over time.
To help custodians set policy and define procedures, we have developed a simple Light Policy Guide. You can download it from here free of charge and members also have a copy in their Standards & Templates folder in the Member Area.