Thermoluminescence is a burst of light emission by warming the leaf or chloroplasts which were illuminated by light. It results from the charge recombination between positively and negatively charged pairs created by photochemical reaction. The origin of four out of seven thermoluminescence bands was assigned: the A, Q, B1 and B2 bands arise from S₃Q_A^-, S₂Q_A^-, S₃Q_B^-·and S₂Q_B^- charge pairs, respectively. Thermoluminescence is applied to the analysis of oxidinzing and reducing side of photosystem II. The following facts were elucidated; 1) By removal of 33 kDa extrinsic protein, S₃ to S₄ transition is inhibited. 2) By Cl^-·depletion, abnomal S₂ state is formed. 3) Replacement of Q_B-quinone with quinone derivatives yields a modified thermoluminescence band. 4) Thermoluminescence is a powerful tool for the study of herbicides and the resistant mutants.