  Anisotropy in the speed of light that has been constrained by
Michelson-Morley-type experiments also generates anisotropy in the Coulomb
interactions. This anisotropy can manifest itself as an energy anisotropy in
nuclear and atomic experiments. Here the experimental limits on Lorentz
violation in 21Ne are used to improve the limits on the Lorentz symmetry in the
photon sector, namely the anisotropy of the speed of light and the Coulomb
interactions, by 7 orders of magnitude in comparison with previous experiments:
the speed of light is isotropic to a part in E-28.
