UV FILTERS FOR FLUORESCENT LIGHTS
Reprinted from The Abbey Newsletter (Dec. 1996), Ellen McCrady, Editor. 7105 Geneva Dr., Austin, TX 78723.
A perennial question in preservation circles has to do with the UV radiation emitted by the fluorescent lamps that light most libraries and archives. UV radiation is known to deteriorate paper; some fluorescent lamps give off large amounts of UV; so people worry about how to control it. Tubular UV filters can be bought through the supply houses, but how can you tell when to replace them? In fact, how can you tell when they are needed in the first place?
Three knowledgeable people from three different countries provided answers to these questions on the Conservation DistList January 8 and 9: Colin Pearson of Australia, who quoted from and confirmed a 1991 article by Murray Frost on museum planning; Helen Alten, Field Services Director for the Upper Midwest Conservation Association; and Andrew Calver, Conservation Manager for Nottingham City. (Hooray for the Internet!)
Murray Frost said that there is no need to worry about UV levels if the lamps are fully enclosed by metal and regular solid acrylic diffusing panels; they always test at less than 75 mwatts per lumen according to a Crawford 760 UV meter. Pearson says to check them at least once every five years. Helen Alten gave similar advice, and said it made sense to exclude visible light too by the use of curtains and shades, since visible light damaged collections.
Andrew Carver measured the light coming through the flat plastic panel below lamps that are installed above a false ceiling, and found they were all low, around 10 mwatts/lumen (except that he wrote mM/lumen by mistake). All the diffusers that actually cover the lamps reduce transmission. All the museums he cares for show 10-40 mW/lumen. He stopped to measure the light fittings above him as he sat at his computer, and found that they emitted only 10 microwatts per lumen, though the diffusers are at least 15 years old. He implied that the end of a diffuser’s life might come when they become so brittle that they crack during relamping, rather than when their filtering ability declines.
