Two conceptually different approaches (broadband-based ERBE (Earth Radiation Budget Experiment) and narrowband-based ISCCP (International Satellite Cloud Climatology Project) approaches), used to derive the TOA (top of atmosphere) longwave radiative fluxes, are compared using the ScaRaB simultaneous narrowband and broadband measurements. Except for very thin cirrus clouds, differences between the ERBE and the ISCCP approaches are in general <10 W m-2 for the TOA LW radiative fluxes. For clear pixels the model-calculated (ISCCP approach) TOA LW radiances are systematically smaller than the observations. Compared with the radiative transfer model used in this study, the ERBE LW angular dependence models are too weakly limb darkened for optically thin clouds but too strongly limb darkened for optically thick clouds, suggesting that more accurate instantaneous TOA LW flux estimations from the ERBE approach would require additional cloud classes based on cloud height and optical thickness.