Fraction of the luminosity in star formation tracing bands contributed by stars living over 100 Myr versus simulation time. The colour scheme is the same as that of Fig. 3. The contribution of long-lived stars is negligible for the Lyman continuum but reaches upward 10% in the FUV, a small but non-negligible fraction. The contamination is stronger for the NUV and TIR tracers, and it is maximum for the U band with a typical value of ~35%.