At this point we don't really know how long the UV filters for fluorescent lamps will last. Some people say ten years, others say longer. Therefore, it is a good idea to test the filters once a year using a UV meter such as the Elsec 762 or Elsec 763. While this is an expenxive piece of equipment, I often recommend that museums share the purchase cost somehow, since it is not a piece of equipment that will be used on a daily basis. Some of the US state historical societies or regional conservation associations have an environmental test kit (that includes a UV meter ) which can be borrowed. The only other time that a monitor will be necessary is to test any new UV filters which are delivered. Sad to say, sometimes the distributors of the filters substitute non-UV filtering materials for those that filter, and it is not always easy to discover the mistake. Please understand, I am not implying that the distributors are doing this on purpose, but mistakes are made and have been made in the past. I once tested a series of windows in the hall of an historic house and found that 6 of the 7 windows had been fitted with UV filtering acrylic sheeting, the 7th had been fitted with standard non-filtering acrylic sheeting. Wendy Claire Jessup President and Conservator Wendy Jessup and Associates, Inc. 210 Little Falls St., Suite 203 Falls Church, VA 22046 USA (703) 532-0788 (703) 532-1661 - fax