The speed of light in vacuum is a constant regardless of frame of reference, I think the thing that gets a lot of people is remember your perception of time changes. So for instance if you take 2 photons and shoot them in opposite directions, they travel apart at the speed of light. If you are one of those photons, from your point of view time has stopped, so you don't appear to be moving to your frame of reference, but the other photon is going away at the speed of light... What I think you might be thinking of as the light thing, there were some experiments not too long ago where someone was able to cause photons to travel slower then the speed of light, but that's not the same as saying that the speed of light in a vacuum has changed. They just caused the photon to travel slower then usual.....