Figure 1.

Relative spectral irradiance profiles of UV-B and blue light sources. UV-B, solid curve; blue light, dashed curve. The culture flasks blocked wavelengths less than 280 nm and thus the UV-C range was excluded. In all treatments, an incandescent growth light of 50 μmol of photons per m² per s was maintained. UV-B treatments added UV-B at culture surface intensities of 0.2, 0.4, or 0.8 W/m² (about 0.5, 1, and 2 μmol of UV-B per m² per s, respectively). Blue light treatments added culture surface intensities of 5 μmol of photons per m² per s (about 1.3 W/m²).