Abstract <p>An analysis of a number of works on modeling the process of the exposure of a photoactive layer lying on an optically matched substrate is carried out. The relationship between Dill’s equations and previously obtained systems of equations is shown. The methods of reducing the system of two Dill partial differential equations to ordinary differential equations, the accuracy of the numerical solution of which can be easily controlled, are considered sequentially. A procedure for using such equations to characterize the photochemical properties of positive photoresists is proposed.</p>