  Using air showers induced by TeV gamma-rays from Mrk 501, the radial
distribution of Cherenkov light is investigated. The shower geometry is
reconstructed from the stereoscopic shower images obtained with the telescopes
of the HEGRA IACT system. We observe a change in the shape of the light pool
with shower energy, and with zenith angle. Data are well reproduced by
Monte-Carlo air shower simulations.
