|Course:||4: Housing Your Collections|
|Lesson:||Lesson 1: Assessing and Improving Your Building|
Light levels in storage areas should be low. Light accelerates deterioration of historical materials. It weakens paper fibers and makes them brittle. It can cause the paper or ink to bleach, yellow, fade, or darken. Any exposure to light, even for a brief time, is damaging, and the damage is cumulative and irreversible. Ultraviolet (UV) light is particularly damaging and should be avoided whenever possible.
Monitoring Light Levels
There are specific devices that can be used to monitor light levels. Light meters measure visible light levels; and UV meters measure ultraviolet light levels – UV is particularly damaging to collections.
Basic light meters can be purchased for just over $100. UV meters are significantly more expensive, costing over $1000. Some meters measure both visible light and UV; these are, of course, more expensive.
Because light meters, particularly for UV levels, are expensive, your best choice is to take some precautions to keep light levels at a minimum. Since damage caused by light is a result of both the intensity and duration of exposure, your goal is to reduce both whenever possible.
Visible light levels are measured in lux (lumens per square meter) or footcandles. One footcandle equals about 11 lux. Ideally, visible light levels should be maintained at 55 lux (5 footcandles).
Incandescent bulbs are the best choice to avoid damaging materials.
The law of reciprocity.