Evolution of the slope of approximating the SSP luminosity following power-law evolution (α(t_∗)) for different photometric bands obtained by combining different synthesis models (see Sect. 3.3 for details). The slope evolution of Q(H) is only shown up to 50 Myr and galex/FUV up to 200 Myr; in addition, the slopes have been smoothed to represent the general aspect of the evolution. We note the non-standard orientation of the y-axis since it refers to α values, whereas the slope is −α.