  Localization of relativistic particles and their position-momentum
uncertainty relations are not yet fully understood. We discuss two schemes of
photon localization that are based on the energy density. One scheme produces a
positive operator-valued measure for localization. It coincides with the number
density operator and reproduces the effective 3x3 polarization density matrix.
Another scheme results in a probability distribution that is conditioned on the
detection. In both schemes the uncertainty relations for transversal position
and momentum approach the Heisenberg bound $\Delta p \Delta z= \hbar/2$
