Question

Under what conditions will light bend?

Answer 1

Light will not bend under any conditions.  It always proceeds straight
along its path.

The path can bend ... either abruptly, at an interface between two
media with different refractive indices, or continuously, when the
index of refraction changes along a line perpendicular to the path
(as it does in the Earth's atmosphere).  

Answer 2

Light CAN in fact bend, but maybe not on Earth. At least as far as I know. Near a black hole, where gravitational force is so strong that even light is sucked, light is bent do
Ue to the gravitational force. This is how astronomers find and identify black holes.