Lyman continuum flux N_Ly vs. the bolometric luminosity L_bol for young H II regions with rising spectra. The black solid line refers to the expected Lyman continuumphoton rate from a single ZAMS star of a given bolometric luminosity. The top axis lists the spectral type corresponding to a given bolometric luminosity taken from stellar models (Thompson 1984; Panagia 1973; Davies et al. 2011). The error bars in the bottom-right corner correspond to a 50% uncertainty for L_bol and N_Ly (Urquhart et al. 2018). At the top, we show the color bar for the physical size of the sources, indicating the physical diameter in parsecs. The red circles and black squares refer to optically thick H II regions (ν_t > 5 GHz) and optically thin H II regions (ν_t < 5 GHz). About 30% of the sample is located in the forbidden region above the solid curve considering a 50% uncertainty. The dotted line represents the empirical relation between L_bol and N_Ly for ionized jets from YSOs, with a power-law index of 0.64 derived by Purser et al. (2016). The red arrows for the optically thick H II regions indicate that the bolometric luminosities are upper limits due to the presence of other H II regions in the same clump.