  We compute the longitudinal proton structure function F_L from the k_T
factorization scheme, using the unified DGLAP/BFKL resummation approach at
small x for the unintegrated gluon density. The differences between the k_T
factorization, collinear factorization and dipole approaches are analyzed and
discussed. The comparisons with the HERA data are made and predictions for the
proposed Large Hadron-Electron Collider are also provided.
