The scope of this investigation is to evaluate different radiation modeling approaches for both Lagrangian and Eulerian flamelet models by comparing them to fully resolved simulation data of a non-premixed flame. The numerical investigations are performed for a well established laminar methane diffusion flame [1]. The available experimental data is used to validate the CFD results, which clearly show that radiation must be considered in this flame to accurately describe the flame structure. Based on the validated CFD results the main focus is to analyze the applicability of radiation modeling approaches within the flamelet framework for unity Lewis number and differential diffusion. An unsteady Lagrangian flamelet model with direct integration of the radiation source term as well as an enthalpy defect formulation for steady and unsteady flamelet calculations are considered. Several model variants are introduced and discussed and the corresponding time scales for mixing, radiation and chemistry are analyzed. Based on the Lagrangian flamelet time and the enthalpy defect, both postprocessed from the CFD solution, flamelet calculations are carried out and detailed comparisons to the CFD simulation results are performed for the temperature and several species along the axis and in several radial slices. The results are finally used to evaluate the different approaches concerning their applicability and accuracy for use in coupled CFD-flamelet simulations. (c) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.