High Quality Content by WIKIPEDIA articles! Kirchhoff`s diffraction formula can be used to model the propagation of light in a wide range of configurations, either analytically or using numerical modelling. It gives an expression for the wave disturbance when a monochromatic spherical wave passes through an opening in an opaque screen. The equation is derived by making several approximations to the Kirchhoff integral theorem which uses Green`s theorem to derive the solution to the homogeneous wave equation.