For constant Yb inversion and increasing pump power in the fiber core, a strong acceleration of the photodarkening (PD) process and reduction of PD loss are observed. The PD parameters determined by fitting the measured curves with the stretched exponential function are linked to the activation and deactivation rates of micro-optic centers (PD complexes). A phenomenological model is shown to reasonably describe the combined effect of Yb inversion and a direct influence of the pump power on these rates. It also offers the possibility to extrapolate the PD parameters to higher powers in the core of Yb fiber lasers.