  The questions of whether a photon can be localized in an arbitrarily small
volume and what is the allowable strength of that localization (the decrease
with distance of the functional form) are questions of current interest. We
propose a measure of localization for the single photon that is the expectation
values of the electromagnetic field strength components in a coherent
wavepacket state of mean photon number unity. As such, we deal with real
quantities that have a physical meaning rather than complex amplitudes. It is
seen that the real parts of complex amplitudes proposed previously as measures
of localization are equal to our field expectations. With this measure, we
examine two test states. The first has a well-resolved momentum. The field
expectations show Gaussian (quadratic exponential) localization in all
directions, although the localization length scale is much larger than the mean
wavelength. For the other test state, with a spherically symmetric momentum
distribution, we find almost exponential localization in all directions at t =
0. The profiles are scale invariant, so choosing the momentum width very large
would make the localization length arbitrarily small. We conclude that there is
no lower bound on the localization length scale of a photon as determined by
this measure.
