Not Zen, but there's "kasina" meditation that sounds similar to this. You might stare at a light source or a colored disc, then close your eyes and watch the afterimage. Repeat. That's it really – very mechanical.
That can lead to wakeful closed-eye hallucinations, some of which are described here:
Not Zen, but there's "kasina" meditation that sounds similar to this. You might stare at a light source or a colored disc, then close your eyes and watch the afterimage. Repeat. That's it really – very mechanical.
That can lead to wakeful closed-eye hallucinations, some of which are described here:
https://en.wikipedia.org/wiki/Closed-eye_hallucination