  Horizons are classical causal structures that arise in systems with sharply
defined energy and corresponding gravitational radius. A global gravitational
radius operator can be introduced for a static and spherically symmetric
quantum mechanical matter state by lifting the classical "Hamiltonian"
constraint that relates the gravitational radius to the ADM mass, thus giving
rise to a "horizon wave-function". This minisuperspace-like formalism is shown
here to be able to consistently describe also the local gravitational radius
related to the Misner-Sharp mass function of the quantum source, provided its
energy spectrum is determine by spatially localised modes.
