Raining Cats and Dogs

The diagram above shows that the UV raining down upon us has a shorter wavelength than visible light, i.e. it has higher frequency and thus more damaging energy. UV is invisible to humans (but not to cats and dogs, curiously). And it is normally divided into 3 broad subranges:-

UV-C: This stuff kills you. Thankfully the Earth’s upper atmosphere stops such radiation from literally frying all life on the planet.

UV-B: This stuff penetrates the earth’s atmosphere and gives us all a nice suntan (and not so nice skin damage, like melanoma). If it reached art, it would surely destroy some objects in a matter of minutes. Thankfully, common float glass stops all UV-B radiation.

UV-A: This is the one to watch out for. Display cases made from float glass will not stop UV-A. This radiation requires filters (either plastic or specially formulated glass) to stop it.

UV damage is cumulative, irreversible and proportional to the exposure, which is the amount of light incident on the object multiplied by the time exposed.

If you were to look at a graph of light levels varying through the year, the exposure would be the area under the graph.

So What Can I Do About It?

There are many solutions available and it would be a mistake to discard them out-of-hand without first knowing the requirements of each item in the collection.

As BSI PAS 198 states, “care of collections requires an understanding of the different categories of object and their different requirements“.

One Size Fits All?

Not really. Based on the popularity, value and condition of the objects, you may choose some, or all, of the following solutions to arrest UV:-

• UV Blocking Plastic and Glass on window facades or the display cases themselves
• Avoiding the use of Compact Fluorescent Lamps (CFLs), since they emit UV
• Motion-activated lighting to restrict the time that the object is exposed
• Electrochromic or electro-optic glass or plastic (which changes its transparency based on an electrical signal), again possibly activated by presence or a timer
• Object-rotation schemes
• Window Blinds, Filters, Curtains, etc

So, It’s Curtains For You?

Not necessarily. Each technique has its cost and benefits. Each technique will be more or less effective.

The choice should be guided by a deep knowledge of the materials on each item. If you want to know more, we have plenty of material in our Blog to inform you.

If that is not enough, or you have a specific item, feel free to contact us and we can discuss the best options to protect your collection.