Chlorophyll is a highly important (green) protein in photosynthesis. There are two forms the protein can take: accessory / antenna chlorophyll and reaction-centre / special-pair chlorophyll. The antenna chlorophyll are used to concentrate the light energy onto the special pair. This occurs through Förster resonance energy transfer (FRET). An electron is excited by a photon, causing it to ‘jump’ to either the S1 or S2 excited states. Heat conversion is used to de-excite any electrons at the S2 level down to the S1. FRET then allows overlapping energy levels in close proximity to transfer excitation between them. Due to the decreasing excitation energies closer to the special-pair chlorophyll, the excitation energy is able to ‘flow’ down. At the reaction centre, the special-pair chlorophyll receive all the transferred excitation energy, allowing for the turnover rate to be closer to its maximum. In photosystem II, this allows for greater proton transport, and in photosystem I for greater NADP and FAD production. Chlorophyll allows the collection of light energy through the light harvesting complex, enabling for the excitation of the special pairs to P700*/P680* states. Without chlorophyll, fewer wavelengths of light would be able to be absorbed and converted to potential energy and chemical energy, reducing efficiency.