Luminosity is reflective awareness. A luminous mental state is one that you have and know that you have. It could be an emotion, a belief or alief, a disposition, a quale, a memory - anything that might happen or be stored in your brain. What's going on in your head?
See also
Luminosity
iswas Alicorn's term for reflective awareness. More recent posts tend to use the term introspection. See also noticing.