Non-photochemical quenching
![Carbon assimilation (red line) tends to saturate at high light intensities, while light absorption (blue line) increases linearly[3]](/uploads/202501/30/Photosynthetic_parameters_of_plants0835.png)
![The relationship between irradiance and carbon assimilation for a monoculture of the plankton Woloszynskia halophila at different pH[4]](/uploads/202501/30/Irradiance_and_carbon_assimilation_for_a_monoculture_of_Woloszynskia_halophila_at_different_pH0835.png)
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.