Quote by xeno108
I'd really would like to know the equation that relates the kinematics of light under gravity.

From the view of a distant observer the speed of light is reduced by the gravitational field (Shapiro delay):
[itex]u = \frac{c}{{1  2 \cdot \frac{\Phi }{{c^2 }}}}[/itex]
with
[itex]\Phi \approx  \frac{{\gamma \cdot M}}{{\left r \right}}[/itex]
The path of the light should be the same as in matter with the same optical density:
[itex]a = 2 \cdot \frac{v}{u} \cdot \left( {v \cdot u'} \right)  u \cdot u'[/itex]