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e. four- to 130-fold greater; Table?2). Following 6?h of UV-B exposure coupled with ecologically realistic levels of PAR and UV-A, the urate- and CA-filtered cultures displayed decreases in light-saturated photosynthetic rates of 5 and 56%, respectively, versus controls receiving no UV-B radiation (Fig.?7). Following a 12?h exposure, cultures exposed to the urate-filtered radiation showed an 11% decrease, whereas CA cultures declined 78% compared with controls receiving no UV-B (Fig.?7). Widely used Biological Spectral Weighting Functions (BSWFs) were applied to the UV-B Regorafenib ic50 radiation for all photosynthetic experiments as summarized in Table?3. It has long been understood that even small deviations from the solar UV-B spectrum in laboratory studies must be recognized and compensated for if ecologically relevant inferences can be made (Smith et?al. 1980; Caldwell et?al. 1986; Helbling et?al. 1992). Attempts to understand solar UV-B effects on photosynthetic organisms are plagued by the difficulty of accurately simulating the solar UV-B spectrum. One lamp that will produce a UV-B emission spectrum very similar to ground-level solar without filtration is the Q-Panel Q-340 UV-A lamp (Fig.?3; Floctafenine Brown et?al. 2000). This lamp has been used in some published algal UV studies (Shelly et?al. 2005; van de Poll et?al. 2005, 2006). The primary shortcoming of the Q-340 lamp is its modest UV-B output. In these studies, the authors reported UV-B emissions of less than 0.6?W?m?2. This is approximately 15% of the UV-B radiation measured in full sunlight (H?der & Tevini 1987). Other lamps must be employed to obtain UV-B fluxes nearer to unfiltered solar levels. To produce significant UV-B radiation in laboratory or solar supplementation experiments, fluorescent UV-B lamps are generally employed. The most widely used UV-B lamps have a peak emission at 313?nm and show relatively minor differences in their emission spectra (McLeod 1997; Johanson & Zeuthen 1998). The UV-B emission from these lamps is very different from the solar ground-level spectrum due to their substantial emission Torin 1 concentration of UV-C (