If light has a maximum speed of c, what frame of reference is that speed determined from? For example, if you were to turn on a light bulb moving at a constant rate and measured when the light in every direction got to one light year away from it's source, wouldn't some of it reach that distance more quickly than the light moving in the opposite direction and wouldn't it be appropriately redshifted? If so, couldn't you use that data to determine a universal frame of reference? It's an obvious question so I'm sure I'm wrong about something. I'd be obliged if someone could explain it to me.