I do not have a problem with the concept of the constant speed of light as it has no mass and therefore no inertia and therefore no relationship to any IFR. However it seems to be expressed as constant in all IFR's which I do not understand. This seems to say that if I am traveling at 1/2c and I shine a torch forward the light moved away from me at c and if I shine the light backwards it also travels away from me at c. This seems to say that, in the first case, the light is travelling away from the point in space that it is created (independent of my IFR), at 1.5c. To clarify this for me, my question is: If I am travelling towards a light source at .5c and I have two light detectors with a set space between them to measure the time that the light takes to transition from one to the other, will the time taken correspond to a speed of c? And, if I decrease my speed to .25c and do the same measurement will the measurement also indicate a speed of c?