21cm brightness temperature lightcones from four runs of 21cmFAST. From left to right: ‘v3 Default’ shows the previous default model, where the source field is calculated on the filtered density grids, ‘CHMF on Grid’ shows a model where there is a one-to-one relationship between cell density and emissivities, based on the integral of the CHMF; ‘v4 No Astro Scatter’ shows the effects of our halo sampler described in Section 2, without any stochasticity in the galaxy properties. We show two cases for the model with stochasticity in the halo mass distribution and galaxy properties, which differ in their interpretations of the scaling relations; ‘v4 Mean Norm’ shows the case where the scaling relations are defined by the mean of each property’ and ‘v4 No Norm’ shows the case where the scaling relations are defined by the mean logarithm. In the latter case, increasing the log-normal scatter also increases the mean emissivities at all wavelengths.