  We discuss in this article the usefulness of the effective Lagrangians
(L_eff) of QED and QCD within the one-loop approximation. Instead of
calculating L_eff via complicated computations with Schwinger's proper-time
technique or Feynman graphs, we prefer to employ the energy-momentum tensor and
the leading-log model. The advantage is that we do not have to demand the
external electromagnetic or color field to be constant. There are also some
critical remarks added which cast doubt on the use of LQCD with covariant
constant fields in explaining the nature of the QCD vacuum.
