Thank you Tibetan_ice.
This is an excellent thread.
I've read many times about seeing a bright light in meditation and visions spontaneously arising from the light.
From time to time, I get some brief vision if I reach the hypnagogic state, but in that place my mind is very scattered.
In my experience of what is called hypnogogic states, thoughts do not remain verbal or vague but projects into hyper-real sights and sounds that are as real or even more vivid than waking reality, the sights and sounds are crystal clear and if you think about a place you'll be there and sometimes if you think about a song you'll just hear the whole song with its lyrics sung so clearly and you wonder why do you remember the lyrics better in sleep than in waking.
It is probably in such states that the practice of visualization in many spiritual traditions succeeds.