  In the present work, the problem about shadow, generalized on domains of
space $\mathbb{R}^n$, $n\le 3$, is investigated. Here the shadow problem means
to find the minimal number of balls satisfying some conditions an such that
every line passing through the given point intersects at least one ball of the
collection. It is proved that to generate the shadow at every given point of
any domain of the space $\mathbb{R}^3$ ($\mathbb{R}^2$) with collection of
mutually non-overlapping closed or open balls which do not hold the point and
with centers on the boundary of the domain, it is sufficient to have four
balls.
