In the two light reactions of photosynthesis

In the two light reactions of photosynthesis PS I produces the strong reductant NADPH while PS II is a strong oxidant.
Photosystem I is an integral membrane protein complex that uses light energy to catalyze the transfer of electrons across the thylakoid membrane from plastocyanin to ferredoxin. The enzyme transfers the electron from reduced ferredoxin to NADP⁺ to complete the reduction to NADPH in PS I.
Photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP.