Three different photoperiods (15 h light: 9 h dark, 12 h light: 12 h dark, and 24 h light: 0 h dark) were employed in growing D. tertiolecta in culture flasks with fluorescent light under the initial light intensity of 100 lE/(m2 s), 4% CO2, temperature of 23 C, and pH of between 6.4 and 7.0 in culture flask. Fig. 6 shows the density of D. tertiolecta as a function of time with three different photoperiods. The maximum cell density approached 9.2 106 cells/mL after a five day cultivation with 24 h light, while the maximum cell density with 15 h light was achieved after 6 days, followed by the 12 h light cycle where maximum cell density was achieved at 6 days. Results indicated that the longer light period significantly increased the cell density of D. tertiolecta and the photoperiod of 24 h light produced the highest biomass during the same cultivation time.