  Based on the gauge symmetry framework, the $U_1$ symmetry of electrodynamics
is violated in the presence of gravity with space-time translational gauge
symmetry in inertial frames. For a light ray, an eikonal equation with
effective metric tensors is derived in the geometric-optics limit. Under these
conditions, the angle of the deflection of light by the sun is calculated to be
$\d \phi \approx 1.75''$ in inertial frames without requiring a gauge condition
such as $\p_\mu A^\mu=0$. In contrast, if the theory is $U_1$ gauge invariant,
one can impose the gauge condition $\p_\mu A^\mu=0$ in the derivation of the
eikonal equation. In this case, one obtains a slightly different effective
metric tensor and a different angle of deflection $\d \phi \approx 1.52''$.
However, because the precision of experiments in the last century using optical
frequencies has been no better than (10 $-$ 20)\% due to large systematic
errors, one cannot unambiguously rule out the result $\d \phi \approx 1.52'$.
It is hoped that the precision of these data can be improved in order to test
Yang-Mills gravity.
