A theory for describing the frequency dependence of the fluorescence response stimulated by a sinusoidally modulated light is developed starting from a hierarchical system of many-body Smoluchowski equations for the reactant molecule distribution functions. A new aspect of the present theory is that it predicts the dependence of phase angle and modulation on the light intensity. Under weak light intensity and at low quencher concentration, the present theory agrees with the theories proposed by Zhou and Szabo and by Molski and Keizer. At high quencher concentration, however, the discrepancy in the predicted values of phase angle and modulation is noticeable even under weak light intensity.