: On Tue, 3 Jan 1995, Alex Barker wrote:
 
: > Does anyone have experience with the use-life (and general usefulness) of
: > fluorescent light UV filters?  How long do they remain effective?
: >
: > Alex Barker
: >
 
It depends on the materials in the filter.  Most of the polyester and acrylic
UV filters now produced should be stable for a decade or more, but some tests
we ran on extruded plastic (acrylic?) sleeves revealed that over time the heat
from the bulb will degrade the plastic, causing minute crazing that allows
light to pass through relatively unfiltered.  This crazing can be easily seen
if the sleeve is gently squeezed.
 
(tech talk:  the aged sleeves exhibited transmission curves that were centered
at about the same frequency (400nm) as the new samples, but the aged curves
were considerably sloped, indicating both an increase in effectiveness caused
by plastic yellowing, and a decrease caused by film degradation (crazing), the
net effect being a decrease in UV filtration)
 
Moral:  if you are going to use extruded sleeves, replace them when they look
darker at the ends, otherwise, purchase or borrow a UV meter and check every
five years or so.
 
John Burke, The Oakland Museum