  Radiation spectra from ultra-relativistic electrons in thin [$T\ll
l_f(\omega)$] and thick [$T\gg l_f(\omega)$] targets are discussed. The method
of simplified averaging is described by examples of Landau-Pomeranchuk-Migdal
effect and radiation at doughnut scattering. General infrared and ultraviolet
asymptotic properties of radiation spectra are discussed.
