  We analyze the results of a 2 years (2011--2012) time series of night sky
photometry performed at the Leibniz Institute for Astrophysics in Potsdam
(AIP). This observatory is located on top of a hill ("Babelsberg"), 22\,km to
the southwest of the center of Berlin. The measurements have been performed
with a Unihedron Sky Quality Meter. We find night sky brightness values ranging
from 16.5 to 20.3 mag$_{\rm SQM}$ arcsec$^{-2}$; the latter (best) value
corresponds to 4.7 times the natural zenithal night sky brightness. We discuss
the influence of clouds, of the Moon and other factors on the night sky
brightness. With respect to the influence of the Moon, it turns out that
Potsdam-Babelsberg, despite its proximity to Berlin, still shows a circalunar
periodicity of the night sky brightness, although it is much weaker than
naturally. The light-pollution-enhancing effect of clouds dominates the night
sky brightness by far. Overcast nights with light pollution (up to 16.5
mag$_{\rm SQM}$ arcsec$^{-2}$) are brighter than clear full moon nights
($\approx$ 18.5 mag$_{\rm SQM}$ arcsec$^{-2}$) in roughly the same proportion
as the latter compared to clear nights with light pollution (20.3 mag$_{\rm
SQM}$ arcsec$^{-2}$).
