  We present an optical picture of linear-optics superradiance, based on a
single scattering event embedded in a dispersive effective medium composed by
the other atoms. This linear-dispersion theory is valid at low density and in
the single-scattering regime, i.e., when the exciting field is largely detuned.
The comparison with the coupled-dipole model shows a perfect agreement for the
superradiant decay rate. Then we use two advantages of this approach. First we
make a direct comparison with experimental data, without any free parameter,
and show a good quantitative agreement. Second, we address the problem of
moving atoms, which can be efficiently simulated by adding the Doppler
broadening to the theory. In particular, we discuss how to recover
superradiance at high temperature.
