  We calculate explicitly the space dependence of the radiative relaxation
rates and associated level shifts for a dipole placed in the vicinity of the
center of a spherical cavity with a large numerical aperture and a relatively
low finesse. In particular, we give simple and useful analytic formulas for
these quantities, that can be used with arbitrary mirrors transmissions. The
vacuum field in the vicinity of the center of the cavity is actually equivalent
to the one obtained in a microcavity, and this scheme allows one to predict
significant cavity QED effects.
