As early as 1953, reports documenting the enhancement of photosynthesis by plants when exposed to flashing light, as compared to the same photon dose under continuous light, were published (Kok, 1953; Myers, 1953). Using the unicellular green alga Chlorella, the effects of varying frequencies and dark/light duration ratios on photosynthetic rates were described. Such results have kindled research on their role in nature and their application in various photobioreactors and algal mass culture facilities, aimed at the production of valuable carotenoids, lipids, and additional products of commercial interest, such as biodiesel. The present review discusses the characteristics of the fluctuating underwater light field in natural waters, bioreactors, and ponds, and summarizes their effects on photosynthesis and growth. Based on the advances in the understanding of the various mechanisms and processes affecting the efficiency and yields of photosynthesis, we discuss their interaction with continuous and intermittent light. The following are examined: a. Post-illumination enhanced respiration b. Photodynamic damage to the 32kd protein of Photosystem II (PSII) c. The xanthophyll cycle d. Thermal-energy dissipation e. In addition, the enhancement phenomenon is examined in relation to the intensity of the ambient light In the context of the present review, it is appropriate to list and compare the different terms and definitions used in the description and study of fluctuating light fields (Table 1). In the following review, the term 'fluctuating light' is used for clarity and consistency.