  We use a scattering formalism to derive a condition of strong coupling
between a resonant scatterer and an Anderson localized mode for electromagnetic
waves in two dimensions. The strong coupling regime is demonstrated based on
exact numerical simulations, in perfect agreement with theory. The strong
coupling threshold can be expressed in terms of the Thouless conductance and
the Purcell factor, thus connecting key concepts in transport theory and cavity
quantum electrodynamics.
