Hi!
as 0.032m is diameter, which Lars might already know.
Well, good point.... 
Maybe this is of help:
http://www.uvequip.co.za/faq.htm
"Of the approximately 456 types of fluorescent lamps made all of the UV or Blacklight lamps make up less than 1% of the total lighting industries lamp production. Therefore there is not much economic incentive to do research to develop low UV depreciation LW phosphors and lamps. The typical UV depreciation of a 4W, 6W, or 8W LW lamp might be as much as 40% to 50% in about 2,400 hours.
UV SYSTEMS has just completed a scientific UV depreciation test using one TripleBright II LW LL-60-352 lamp. From this test it was determined that the UV output of that lamp depreciated to about 80% of initial output (a 20% reduction) after about 7,000 hours of use. While this was only a sample of one, it could be typical of all LL-60-352 lamps."
And some more tests (you can see a set-up how to determine the depreciation in this paper, too):
http://www.uvsystems.com/articles/Life_SW_Filters_UV_Depreciation_Lamps.pdf
CU Lars.