as we know that light is an electromagnetic wave and consists of photons. but, basically Photons always travel at the speed of light, but they lose energy when travelling out of a gravitational field and appear to be redder to an external observer. The stronger the gravitational field, the more energy the photons lose because of this gravitational redshift. The extreme case is a black hole where photons from within a certain radius lose all their energy and become invisible. Indeed, light in the vicinity of such strong gravitational fields exhibits quite bizarre behavior. I hope amish it will help you.