  We focus on the astrobiological effects of photospheric radiation produced by
main-sequence stars of spectral types F, G, K, and M. The photospheric
radiation is represented by using realistic spectra, taking into account
millions or hundred of millions of lines for atoms and molecules. DNA is taken
as a proxy for carbon-based macromolecules, assumed to be the chemical
centerpiece of extraterrestrial life forms. Emphasis is placed on the
investigation of the radiative environment in conservative as well as
generalized habitable zones.
