Non-photochemical quenching (NPQ) is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity. It involves the quenching of singlet
excited state chlorophylls (Chl) via enhanced
internal conversion to the
ground state (non-radiative decay), thus harmlessly dissipating excess excitation energy as heat through molecular vibrations. NPQ occurs in almost all photosynthetic
eukaryotes (algae and plants), and helps to regulate and protect photosynthesis in environments where
light energy absorption exceeds the capacity for light utilization in
photosynthesis.