Fractional error when using Eq. (2) to determine L_bol compared to the true L_bol for synthesised stellar populations with different cluster masses as a function of time. To create these synthesised populations, we used SLUG with the median metallicity, extinction, and electron density found for the HII regions in this sample. The solid lines indicate the median of 100 simulations and the shaded region indicates the spread between the fifth and 95th percentiles for each cluster stellar mass. The dashed black line shows where the IMF-averaged estimate given by Eq. (2) is equivalent to the true bolometric luminosity from SLUG, L_{bol,  SLUG}. Above this line, Eq. (2) overestimates the true L_bol of these synthesised populations.