Total stellar bolometric luminosity–pre-cluster molecular cloud mass relation. The solid curve shows the prediction from the optimal sampling method, where the cluster mass relates to the mass of each star formed in that cluster deterministically, according to Eqs. (7)–(10). The total stellar luminosity is calculated with Eq. (12). The red circles are the observational data adopted from Urquhart et al. (2022); specifically their clumps related to HII regions.