Effective refractive index (n_eff) predicted by the Bruggeman EMA (solid line), and by the Maxwell-Garnett EMA (dash-dotted line) as a function of porosity. The open circles indicate the refractive index and the corresponding porosity obtained by laser optical interference and by the Lorentz-Lorenz equation (Eq. (8)), respectively. The inset presents a zoom-in of the low porosity range.