Colddisk of an A6V star: normalised SED (solid line in blue). Left: bright debris disc with f_d ~ 10⁻³. Right: very bright debris disc with f_d ~ 5 × 10⁻³. The dash-dotted blue line shows the contribution of unbound s ≤ s_blow grains. The dotted blue line represents the contribution of grains in the halo beyond the main disc. The red line corresponds to a simulation that only takes s ≥ s_blow grains into account.