  Light is the richest information retriever for most physical systems,
particularly so for astronomy and cosmology, in which gravitation is of
paramount importance, and also for solid state defects and metamaterials, in
which some effects can be mimicked by non-Euclidean or even non-Riemannian
geometries. Thus, it is expedient to probe light motion in geometrical
backgrounds alternative to that of general relativity. Here we investigate this
issue in generic metric-affine theories and derive (i) the expression, in the
geometrical optics (eikonal) limit, for light trajectories, showing that they
still are null (extremal) geodesics and thus, in general, no longer
autoparallels, (ii) a generic {formula} to obtain the relation between source
(galaxy) and reception (observer) angular size (area) distances, generalizing
Etherington's original distance reciprocity relation (DRR), and then applying
it to two particular representative non-Riemannian geometries. First in
metric-compatible, completely antisymmetric torsion geometries, the generalized
DRR is not changed at all, and then in Weyl integrable spacetimes, the
generalized DRR assumes a specially simple expression.
