  In the framework of noncompact lattice QED with light fermions, we derive the
functional dependence of the average energy per plaquette on the bare
parameters using block-spin Renormalization Group arguments and assuming that
the renormalized coupling vanishes. Our numerical results for this quantity in
$8^4$ and $10^4$ lattices show evidence for triviality in the weak coupling
phase and point to a non vanishing value for the renormalized coupling constant
in the strong coupling phase.
