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Using advanced near UV photoemission spectroscopy PES in constant final state mode CFSYS with very high dynamic range, we investigate the triple cation lead halide perovskite Cs0.05 MA0.17FA0.83 0.95Pb I0.83Br0.17 3 and gain detailed insights into the density of occupied states DOS in the valence band and band gap. A valence band model is established which includes the parabolic valence band edge and an exponentially decaying band tail in a single equation. This allows to precisely determine two valence band maxima VBM at different k vectors in the angle integrated spectra, where the highest one, resulting from the VBM at the R point in the Brillouin zone, is found between 1.50 eV to 1.37 eV relative to the Fermi energy EF. We investigate quantitatively the formation of defect states in the band gap up to EF upon decomposition of the perovskites during sample transfer, storage, and measurements During near UV based PES, the density of defect states saturates at a value that is around four orders of magnitude below the density of states at the valence band edge. However, even short air exposure, or 3h of X ray illumination, increased their density by almost a factor of six and 40, respectively. Upon prolonged storage in vacuum, the formation of a distinct defect peak is observed. Thus, near UV CFSYS with modelling as shown here is demonstrated as a powerful tool to characterize the valence band and quantify defect states in lead halide perovskites