Exposure levels are monitored by calculating total exposure, which is the product of the intensity of the source multiplied by the length of exposure. All light is damaging, so lights should be turned off as much as possible in the stacks. In a situation where study carrels or desks are located in the stacks, carrels should be illuminated by individual lamps. The stack ranges should have timer switches or, at least, switches with signs that remind people to turn off the lights when they are not needed. Direct sunlight and skylights should be avoided since they emit so much UV radiation.
Daylight contains different kinds of light.
Thus, UV is most intense when it comes straight downward from a light source. Fluorescent illumination in direct contact with collection materials should be filtered. The preferred way to filter fluorescent tubes is by using plastic coverings on the light fixtures. Covers, lenses, or glazing should be made of UV-filtering acrylic or polycarbonate. An alternative to plastic glazing is to fit each fluorescent tube with an UV-filtering sleeve, especially the ends where UV emissions are the highest.