  The effective Lagrangian of electromagnetic fields at the cubic order in
field strength has been considered. This generalized Lagrangian is motivated by
electrodynamics on non-commutative spaces. We find the canonical and
symmetrical energy-momentum tensors and show that they possess non-zero traces.
The propagation of a linearly polarized laser beam in the external transverse
magnetic field is investigated. We evaluate the induced ellipticity which
allows us to obtain a constraint on parameters introduced from the PVLAS
experimental data.
