A new algorithm has been proposed for the calculation of the electric field intensity in stratified multilayered films when light is incident on the system. The algorithm utilizes matrix formulas based on Abeles's formulas for the calculation of reflectance and transmittance. Equations for calculating patial absorptance due to a certain depth in the films are also derived. Some examples of the application of the electric field description are given for the analysis of three kinds of reflection spectroscopic methods which use metal surfaces: reflection-absorption, surface electromagnetic wave, and metal overlayer ATR methods. The algorithm given here offers a useful tool in understanding the mechanism of light absorption in various spectroscopic methods, and is convenient to use where intensity of the IR spectrum is of interest.