  We present a pilot study of atmospheres of accreting magnetic white dwarfs
irradiated by intense fluxes at ultraviolet to infrared wavelengths. The model
uses a standard LTE stellar atmosphere code which is expanded by introducing an
angle-dependent external radiation source. The present results are obtained for
an external source with the spectral shape of a 10000K blackbody and a freely
adjustable spectral flux. The model provides an explanation for the observed
largely filled-up Lyman lines in the prototype polar AM Herculis during its
high states. It also confirms the hypotheses (i) that irradiation by cyclotron
radiation and other radiation sources is the principle cause for the large
heated polar caps surrounding the accretion spots on white dwarfs in polars and
(ii) that much of the reprocessed light appears in the far ultraviolet and not
in the soft X-ray regime as suggested in the original simple theories. We also
briefly discuss the role played by hard X-rays in heating the polar cap.
