Optical properties of bilayer organic light-emitting diodes (OLEDs) based on MEH-PPV (2-methoxy, 5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene) and Alq3 (tris(8-hydroxy-quinolinato) aluminum) are investigated in this paper. Numerical method solving 1D model based on driftdiffusion, continuity and Poisson`s equations extended by boundary conditions in treatment of internal organic interface is applied. The obtained space charge densities were employed in the emissive singlet exciton continuity equation resulting in the singlet exciton distribution and the emission zone profile. Dipole methods were utilized for the simulation of light emission in a layered medium. The electroluminescence (EL) spectra of OLED are considered by taking into account dominant interference effects. The exciton quenching near electrodes, allowing for a dominant nonradiative decay, is treated through effective emission zone narrowing.