I would not put a lot of thought into "a beam of light" running the edge of the razor,,, that is a reflection of light that you see, not a beam.
I'm not trying to be a smart a$$, just that reflections are being made here. Reflections can sometimes tell you that you have honed the distance from toe to heal & sometimes they can tell you if you have laid a bevel on top of another bevel,,, but they cannot indicate a perfect edge. Too much reflection can hide microchips in the edge though.