Water Spliting

Light Reaction
The photochemical phase is also known as the light reaction. It involves the absorption of light, the splitting of water, the release of oxygen, and the production of high-energy chemical intermediates (ATP and NADPH). The process involves a large number of complexes.
Within Photosystem I (PS I) and Photosystem II (PS II), the pigments are arranged into two distinct photochemical light-harvesting complexes (LHC). The photosystems are called according to the order in which they were discovered, not their function during the light reaction.
Except for one molecule of chlorophyll a, each photosystem contains all of the pigments. The reaction centre is formed by a single chlorophyll molecule. PS I is named after the reaction centre chlorophyll a, which has an absorption peak at 700 nm. PS II has an absorption maximum at 680 nm, hence the name PS680.