Light passes through several chlorophyll molecules to special reaction-center chlorophyll that generates excited electrons for photosystem I.

In cyclic phosphorylation, hydrogen split from water during noncyclic photophosphorylation is pumped across the thylakoid to the outside using energy derived from the release of electrons from chlorophyll.  The electrons are returned to the chlorophyll molecule and the hydrogens are used to drive ATP through chemiosmosis.

In noncyclic photophosphorylation, water is enzymatically split to provide hydrogen to be pumped across the thylakoid and electrons across the electron-transport chain.  The electron and hydrogens are used to reduce NADP to NADPH, used in the Calvin-Benson reactions.