I can't get even similar irradiance values from lamps.


as 0.032m is diameter, which Lars might already know.

Well, good point.... :wink:

Maybe this is of help:


"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):


CU Lars.