Convective efficiency and gravity-darkening exponent in the HR diagram. The models were computed with the GRANADA code and the masses range from 0.8 up to 3.16 M_⊙. Dashed line indicates the locus of the f = 0.5 (Eq. (10)). This line roughly divides the HR diagram in envelopes with high convective efficiency (right) and low convective effciency envelopes (left). The critical log T_eff at the ZAMS is around 3.9.