I read (I think ) that part of relativity theory is that a strong gravitational field distorts the uniform passage of time. If this is true and a lightwave 'travelling' to Earth passes a star near its intense gravitational field (a gravity 'lens') does the gravitational field distort the 'timing' of the speed of light and for a small duration of time the light-wave slows a bit until it leaves the influence of the star's gravity? If this is so could you say the speed of light itself was slightly less while the lightwave was passing through the star's gravity?
Answer
We need to be a bit cautious about making over simplified statements in this area because it is a minefield for the unwary. However it is true that as observed by observers far from the star, the gravitional field does affect the elapsed time for objects within it and it also affects the distances travelled by those objects. The net result is that the speed of light does vary with distance from the star.
For more details you might want to look at the questions Photons emitted at the event horizon? and Speed of light originating from a star with gravitational pull close to black-hole strength? for a more detailed discussion of this.
The time dilation is a real effect and has been experimentally measured. In 1971 Hafele and Keating measured the affect of the Earth's gravity on atomic clocks. You ask about this in your comment to user3138766's answer, and the answer is that the time dilation slows everything. If you hovered near a black hole for a while then returned to Earth you would find you were younger than your contemporaries on Earth.
Gravitational lensing is due to the curvature of spacetime. The change in the speed of light in effect changes the refractive index of the space it's travelling through, and this bends the light in an analogous way to the bending of light by a lens.
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