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