The subtlest level of mental activity (mind), which continues with no beginning and no end, without any break, even during death and even into Buddhahood. It is individual and constitutes the mental continuum of each being. It is naturally free of conceptual cognition, the appearance-making of true existence, and grasping for true existence, since it is more subtle than the grosser levels of mental activity with which these occur. It has nothing to do with "light."
J Hopkins: clear light.