UV Transmittance Values Reported in Berkeley Lab WINDOW
Friday, September 1, 2017
Berkeley Lab WINDOW reports three different values in the whole window report for transmittance.
Tdw-K (TKR in the Standards file) is weighted by the old Krochmann damage function which purports to correct for the sensitivity of many materials. While more meaningful than TUV, it is also included for "historical" purposes, because it was included in ISO 9050 and perhaps in CEN standards before the latest recommendations by CIE.
Tdw-ISO (TDW in the Standards file) is weighted using a function recommended in the CIE standard which also derives from the work of Krochmann, but is considered to have more general validity. We had the opportunity to harmonize with CIE when the NFRC standard was last updated and we took it.
Tuv (TUV in the Standards file) is the unweighted transmittance over the ultraviolet. Because it is unweighted by a "detector" function, TUV has no correction for the spectral sensitivity of materials to radiation damage. It doesn't even cover the spectral range in which damage occurs, just the "uv" meaning below the visible. This function is included for historical comparison purposes only, since many manufacturers used this function before corrected functions were available. It is believed to have little meaning.