Protein phosphatase specifically required for efficient dephosphorylation of the light-harvesting complex II outer antennae (LCHII) and transition from state 2 to state 1 (PubMed:20176943, PubMed:20126264). State transition plays a central role in response to environmental changes and allows to adjust to changing light conditions via the redistribution of light excitation energy between photosystem II (PSII) and photosystem I (PSI) in a short time by relocating LHCII proteins (Probable). Mainly responsible for the dephosphorylation of Lhcb1 and Lhcb2 but not of the photosystem II core proteins (PubMed:20176943). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 magnesium or manganese ions per subunit. Associates with the stroma lamellae of the thylakoid membranes. Belongs to the PP2C family.