Rigorous diffraction theory is a reliable tool to quantify the absorption enhancement in textured thin film solar cells. We provide a line of arguments that make the insights from such an involved analysis accessible to a broader community by using a scalar approach. We show that the scattering response from a textured surface as calculated by a simple scalar model can be related to the measured external quantum efficiency of a solar cell and double-check this model by rigorous calculations. This approach allows estimating the performance of a textured thin film to a certain extent without any sophisticated numerical analysis.