A new approach for the simulation of OLEDs based on a plane wave field expansion is proposed. Exact general formulae are given that allow for the calculation of their optical characteristics including losses in all layers in an arbitrary OLED structure. The S-matrix approach is used which ensures numerical stability of the algorithm. A simple way is proposed to take into consideration non-coherent reflections in a thick substrate. The validity of the model is demonstrated by comparing with experimental data. (C) 2011 Elsevier B.V. All rights reserved.