An historical and update review about the ability of cloroplasts to dynamically regulate the excitation energy between photosystems has been made. Now a days is generally accepted that plants contain two photosystems, photosystems 2 (PS2) and photosystem 1 (PS1). They are co-operativelly involved in the process of light energy transduction and are located in the thylakoid membranes of the cloroplasts. Changes in light conditions induce State 1-Satet 2 transitions. The so termed State 1 arises when thylakoids are equilibrated in light absorbed preferentially by PS1 and results from the photochemical apparatus adapting to direct a greater proportion of the absorbed radiation to PS2 than PS1. The opposite situation results in the appearance of State 2.This review is complemented with new experimental results which seem to indicate that a migration of PS2 light harvesting (LHC2) to PS1 located in non-appreses regions of the thylakoid membrane does not occur.Peer reviewed