Left: brightness temperature of the protostellar disks calculated from the full Planck equation as a function of the evolutionary stage (bolometric temperature). Right: transition between disks with substructures and without substructures at T_bol ∼ 200 K, which is not due to the optical depth. We do not see a discontinuity for the brightness temperature to dust temperature ratio (T_{bright,Planck}/T_dust) at 200 K. For optically thick disks, the T_{bright,Planck}/T_dust ratio should be close to 1 (horizontal black line). We adopted the dust temperature from Equation (1), and excluded the circumbinary disks.