PAR was measured in each field treatment to assess to what extent it is affected by the windows. There was no significant difference in PAR between UV-filtering and UV-transmitting windows. The mean PAR in UV-filtered plots was 1324 µmol m-2 s-1, the standard deviation (σ) was 348 µmol m-2 s-1. The mean PAR in UV-transmitted plots was 1343 µmol m-2 s-1 (σ = 340 µmol m-2 s-1). PAR in site reference sample sites (mean = 1472 µmol m-2 s-1, σ = 345 µmol m-2 s-1) was slightly but significantly higher than both UV-filtered and UV-transmitted windows (P = 0.0002 and P = 0.006, respectively). UV was significantly lower under UV-filtering windows relative to UV-transmitting windows (approximately 98% reduction from 91.3 to 1.6 µmol m-2 s-1; P < 0.0001, σ = 25.5 µmol m-2 s-1 and 0.5 µmol m-2 s-1, respectively). Site reference sites had higher UV than both UV-filtered and UV-transmitted sites (mean = 105 µmol m-2 s-1, σ = 34.5 µmol m-2 s-1; P < 0.0001 and P = 0.001, respectively). Mean total light intensity of each treatment per month did not differ between the two windows (DFn = 1, DFd = 28, F = 0.954, P = 0.337).