Fig. 6 shows the growth rate of the Spirulina with different red light illumination time and the control group. As indicated
in Fig. 6, Spirulina exposed to red light grows faster than the control group. The growth rate of Spirulina with an illumination
time of 2 h increased not as significant as that with 4–12 h illumination everyday. In addition, huge change is observed in
the growth rate of Spirulina with an illumination time of 4–8 h, and the growth rate of Spirulina is nearly invariable after
illumination time of 8 h. The optimal time with the red light is 8 h and the maximum dry matter content is 1.440 g/L which
increases by 67.64% compared with the control group.