The light regime inside a photobioreactor is characterized by a light gradient with full (sun)light at the light-exposed surface and darkness in the interior of the bioreactor. Consequently, depending on the mixing characteristics, algae will be exposed to certain light/dark cycles. In this study the green alga Chlamydomonas reinhardtii was cultivated under five different light regimes: (1) continuous illumination; (2) a square-wave light/dark cycle with a light fraction () of 0.5 and a duration (tc) of 6.1 s; (3) =0.5, tc=14.5 s; (4) =0.5, tc=24.3 s and (5) =0.8, tc=15.2 s. The biomass yield on light energy, protein per photons, decreased under light/dark cycles (=0.5) in comparison to continuous light (CL), from 0.207 (CL) to 0.117–0.153 g mol−1 (=0.5). Concomitantly, the maximal specific photosynthetic activity, oxygen production per protein, decreased from 0.94 (CL) to 0.64–0.66 g g−1 h−1 (=0.5). Also the quantum yield of photochemistry, yield of the conversion of light energy into chemical energy, decreased from 0.47 (CL) to 0.23 (=0.5, tc=24.3 s). Apparently, C. reinhardtii is not able to maintain a high photosynthetic capacity under medium-duration light/dark cycles and since specific light absorption did not change, light utilization efficiency decreased in comparison to continuous illumination.
Janssen, M., de Winter, M., Tramper, J., Mur, L. R., Snel, J., & Wijffels, R. H. (2000). Efficiency of light utilization of Chlamydomonas reinhardtii under medium-duration light/dark cycles. Journal of Biotechnology, 78, 123-137. https://doi.org/10.1016/S0168-1656(99)00233-3