Departure coefficients for the lower and upper levels of the O I 777 nm triplet in the ⟨3D ⟩ model solar atmosphere. The departure coefficients as predicted by the reduced model atom overlap with those predicted by the comprehensive model atom in this plot. Also shown are the departure coefficients predicted from the comprehensive model atom but with all fine structure above the triplet (i.e. above 10.74 eV) collapsed (“Less fine structure”), and from the comprehensive model atom but with all fine structure down to and including the ground level collapsed (“No fine structure”), illustrating the importance of resolving fine structure in non-LTE model atoms.