Two radiance models within LOWTRAN 6 are compared: the ‘zero-order’ scattering, as implemented in standard LOWTRAN 6, and the ‘conservative’ scattering algorithm. The comparison is performed for slant paths from ground to space in infrared window regions 3-5 μm and 8-14 μmi. Deviations between both models depend on the spectral region and the visibility. Considerable discrepancies of more than 10 K in radiation temperature occur for 90° zenith angles, i.e. paths tangent to the Earth's surface. It is shown that an artifact, namely the radiance dip near the 90° zenith angle, does not occur in the ‘conservative’ scattering model.