Light extraction from organic light emitting diodes (OLEDs) is attracting considerable interest as being crucial for enhancing the energy efficiency in lighting applications. Light extraction can be realized by lithographically defined internal diffraction gratings or stochastic scattering centers. The former approach needs in addition an external optical layer for scrambling the angularly dependent emission spectra in order to avoid color shifts . Micro lens arrays cannot only be used for fulfilling this task but they can also be used for enhancing the luminosity into a specific direction. We demonstrate recent advances towards high efficiency OLEDs with high directionality. In addition to the relevant technologies we have also developed a comprehensive simulation software for the quantitative description of the light propagation inside the devices. Here, a particular challenging task is the description of multiple and coherent optical scattering. We have recently developed a software for the exact simulation based on a scattering matrix formalism .
 T. Bocksrocker, J. B. Preinfalk, J. Asche-Tauscher, A. Pargner, C. Eschenbaum, F. Maier-Flaig and U. Lemmer, White organic light emitting diodes with enhanced internal and external outcoupling for ultra-efficient light extraction and Lambertian emission Opt. Expr. 20, A932 (2012).
 A. Egel, U. Lemmer, Dipole emission in stratified media with multiple spherical scatterers: Enhanced outcoupling from OLEDs, Journal of Quantitative Spectroscopy and Radiative Transfer 148, 165 (2014).