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Light is affected by local inhomogeneities in its propagation, which mayalter distances and so cosmological parameter estimation. In the era ofprecision cosmology, the presence of inhomogeneities may induce systematicerrors if not properly accounted. In this vein, a new interpretation of theconventional Dyer-Roeder (DR) approach by allowing light received from distantsources to travel in regions denser than average is proposed. It is argued thatthe existence of a distribution of small and moderate cosmic voids (or "blackregions") implies that its matter content was redistributed to the homogeneousand clustered matter components with the former becoming denser than the cosmicaverage in the absence of voids. Phenomenologically, this means that the DRsmoothness parameter (denoted here by $\alpha_E$) can be greater than unity,and, therefore, all previous analyses constraining it should be rediscussedwith a free upper limit. Accordingly, by performing a statistical analysisinvolving 557 type Ia supernovae (SNe Ia) from Union2 compilation data in aflat $\Lambda$CDM model we obtain for the extended parameter,$\alpha_E=1.26^{+0.68}_{-0.54}$ ($1\sigma$). The effects of $\alpha_E$ are alsoanalyzed for generic $\Lambda$CDM models and flat XCDM cosmologies. For bothmodels, we find that a value of $\alpha_E$ greater than unity is able toharmonize SNe Ia and cosmic microwave background observations therebyalleviating the well-known tension between low and high redshift data. Finally,a simple toy model based on the existence of cosmic voids is proposed in orderto justify why $\alpha_E$ can be greater than unity as required by supernovaedata.

Studying light propagation in a locally homogeneous universe through an extended Dyer-Roeder approach