...according to my physics model:
Light is variance in gravity. More particularly, it is a wave propagating through gravity representing a change in the origin of that gravitational force's position.
This strictly speaking doesn't depend upon my model of gravity, which I haven't elaborated greatly on yet; as far as I know it should work just as well in any model of gravity. In a particulate gravity system, photons are just gravitons with different values than their predecessors.
It predicts some curious behavior for isolated particles, however.