Figure 5: Binned optical quasar luminosity function from the work of Croom et al. (; their Figure 11) in six redshift intervals, from to . Measurements where obtained from the 2dF QSO Redshift Survey (2QZ;  blue), the 2dF-SDSS LRG and QSO survey (2SLAQ; ; green), and combining the latter with the general SDSS QSO sample (; red). The dotted line shows the measured luminosity function in the range for reference. The strong evolution of the QSO luminosity function is clearly seen in this figure. This evolution is best fitted by a LEDE model, as described in the text.