We introduce a new approach for measuring both the effective medium and the
transport properties of light propagation in heterogeneous media. Our method
utilizes the conceptual equivalence of frequency variation with a change in the
effective index of refraction. Experimentally, we measure intensity
correlations via spectrally resolved refractive index tuning, controlling the
latter via changes in the ambient pressure. Our experimental results perfectly
match a generalized transport theory that incorporates the effective medium and
predicts a precise value for the diffusion constant. Thus, we directly confirm
the applicability of the effective medium concept in strongly scattering
materials.Comment: 5 pages, 5 figure