Photosystem I is a protein complex found in the thylakoid membranes of chloroplasts in plants and algae. It plays a crucial role in the process of photosynthesis by capturing light energy and converting it into chemical energy. This complex primarily absorbs light at a wavelength of 700 nanometers, which excites electrons and initiates a series of reactions. The excited electrons from Photosystem I are transferred to a primary electron acceptor and then passed through a series of proteins in the electron transport chain. This process ultimately leads to the production of NADPH, a key energy carrier used in the synthesis of glucose during the Calvin cycle.