  The HEGRA system of Imaging Atmospheric Cherenkov Telescopes (IACTs) detects
Cherenkov light produced by air showers. The concept of stereoscopic
observation with the five HEGRA telescopes allows the reconstruction of various
shower parameters, for example the shower direction, the location of the shower
core and the energy of cosmic rays. One of the telescopes was modified so that
measurements of the spectrum and the polarization of Cherenkov light with the
HEGRA system were possible. The experimental setup is described and preliminary
results presented.
