  Born-Infeld electromagnetic waves interacting with a static magnetic
background are studied in an expanding universe. The non-linear character of
Born-Infeld electrodynamics modifies the relation between the energy flux and
the distance to the source, which gains a new dependence on the redshift that
is governed by the background field. We compute the luminosity distance as a
function of the redshift and compare with Maxwellian curves for supernovae type
Ia.
