  We establish a new model of coupling between a cosmic dark fluid and
electrodynamic systems, based on an analogy with effects of electric and
magnetic striction, piezo-electricity and piezo-magnetism, pyro-electricity and
pyro-magnetism, which appear in classical electrodynamics of continuous media.
Extended master equations for electromagnetic and gravitational fields are
derived using Lagrange formalism. A cosmological application of the model is
considered, and it is shown that a striction-type interaction between the dark
energy (the main constituent of the dark fluid) and electrodynamic system
provides the universe history to include the so-called unlighted epochs, during
which electromagnetic waves can not propagate and thus can not scan the
universe interior.
