A phenomenon called flashing light effect (FLE) has very solid theoretical basis, which lies in the intimate metabolic mechanisms of photosynthesis. Light is utilized instantly, but the syntheses of cell components are slow processes compared to that. Hence, FLE is crucial to increasing biomass quality and quantity. Having it as a tool in microalgal cultivation, methods are extremely beneficial. The frequency of light/dark cycles can be optimized according to cell pigments abilities of any particular strain. This can be done in modern photobioreactor (PBR) design where geometry is chosen on the basis of computing fluid dynamics simulations. Many scenarios of flow distributions are analyzed before choosing optimized frequency of light/dark cycles inside the vessel. Further, real active experiments to discriminate the competing hypotheses of the models must be planned and executed. This chapter analyzes in detail major advantages of growth when FLE is applied.