Perhaps it's how meditation balances the sympathetic and parasympathetic nervous systems. But yeah, I know when my mediation is deepening because the rhythmic pulsation up my spine into my base brain begins.
I'm not talking about the general effect of meditation which is to relax the body and increase the flow throughout the body. I was talking very specifically about this concept of spherical expanding waves of light. To make an analogy, it resembles a moderately white light expanding from a centre. See my other comment where I describe how such a phenomena could be healing and restorative using a physical analogy.