Maintaining the value of artworks has a number of characteristics, not least the importance of limiting light damage, most evident in the fading of more fugitive colours.

Unfortunately, not only does all light cause some form of damage, but also its effect is cumulative. The concept of "resting" works-of-art by taking them off display does limit light damage but in no way can restore them to an earlier state.

How then can the art collector maintain a responsible line between having works on display, and thus being able to enjoy/exhibit them, whilst at the same time limiting their fading, and maintaining their value for future generations?

The traditional gallery route has been to provide low light levels in areas where light sensitive artworks are on display. Whilst this may satisfy the conservators, it rarely keeps the visitors happy, as they peer into dimly lit showcases or gallery corners. Healthy young eyes may be able to see such artworks clearly, but the elderly have increasing trouble, particularly where the artworks are dark with complex textures.

The approach to this difficult problem developed by the Victoria & Albert Museum in London is to use a combination of Just Noticeable Fades or JNF (the unit measure established to monitor the fading of artworks) and blue wool standards. The ISO blue wool standard is the standard light sensitivity test, whereby ISO 1 is typical of very light-sensitive objects such as colour prints, and ISO 8 is some 2,000 times more stable and equates to robust pigments such as earth colours and graphite.

The V&A has estimated that there are about 30 steps of JNF, ie. a level of fading which the human eye can just detect, between full colour and complete fade. They consider 50 years to one JNF as an acceptable rate of fading, i.e. that no discernible effect can be detected in one generation (25 years) but there is just noticeable damage at the end of two generations.

By combining the ISO blue wool standard and acceptable rates of fade (i.e. one JNF every 50 years), it is possible to calculate for how many hours a year at various light levels artworks can be safely exhibited.

Whilst this may all sound rather esoteric to the art collector, it does mean that a scientific method of calculating the likely damage of various levels of light on artworks can be undertaken, and a regime put in place to limit that damage. All of which can only benefit the maintenance of value.