Photosynthetic pigments are arranged in light-harvesting clusters or photosystems in the thylakoid membrane. Several hundred accessory pigments capture light energy and channel the energy to a chlorophyll a molecule at the reaction centre of the photosystem.There are two photosystems. Photosystem I occurs mainly in the lamellae and has at its reaction centre P700, a chlorophyll a molecule with a peak wavelength of absorption at 700nm and photosystem II occurs mainly in the thylakoids and accordingly is P680.