  Contrary to some widespread intuitive belief, the night sky brightness
perceived by the human eye or any other physical detector does not come
(exclusively) from high in the sky. The detected brightness is built up from
the scattered radiance contributed by all elementary atmospheric volumes along
the line of sight, starting from the very first millimeter from the eye cornea
or the entrance aperture of the measuring instrument. In artificially lit
environments, nearby light sources may be responsible for a large share of the
total perceived sky radiance. We present in this paper a quantitative
analytical model for the sky radiance in the vicinity of outdoor light sources,
free from singularities at the origin, which provides useful insights for the
correct design or urban dark sky places. It is found that the artificial zenith
sky brightness produced by a small ground-level source detected by a
ground-level observer at short distances (from the typical dimension of the
source up to several hundred meters) decays with the inverse of the distance to
the source. This amounts to a reduction of 2.5 mag/arcsec2 in sky brightness
for every log10 unit increase of the distance. The effects of screening by
obstacles are also discussed.
