On the possibility of measuring $F_L(x,Q^2)$ at HERA using radiative   events
  It is shown that a significant measurement of the longitudinal structure function $F_L(x,Q^2)$ can be performed at HERA, for $Q^2 = 2 GeV^2$ and $Q^2 = 5 GeV^2$ and for x around $10^{-4}$, using radiative events with hard photon emission collinear to the incident lepton beam, under the present running conditions and with an integrated luminosity of 10 $pb^{-1}$. The influence of experimental conditions is discussed. 
L. Favart, M. Gruw\'e, P. Marage, Z. Zhang