The pigments involved in photochemical reactions are organised into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II).

• In PS I, the reaction centre chlorophyll-a has an absorption peak at 700 nm, hence is called P700.
• In PS II the reaction centre chlorophyll-a has an absorption maxima at 680 nm, and is called P680.