The degradation of J-aggregates of thiacarbocy~nlne dye (THIATS) exposed to visible radiation is experimentally investigated. A model that allows s consistent description of photodegradation of J-aggregates in s solution is proposed. L-mlnescence quencher molecules are formed with the participation of monomer dye molecules in s solution under action of the light. These molecules, when diffusing to the aggregates for a time of nearly 10 s, are adsorbed on their surface and participate in quenching of exciton luminescence of the J-aggregates.