Whether it is the contemplation of the sun as described in the Sutra on the Contemplation of Amitayus, the contemplation of white bones, or any other forms of contemplative practice, upon reaching accomplishment, the vision will spontaneously appear whether the eyes are open or closed, without deliberate mental effort. Naturally, if conscious effort is applied, the vision will become even more distinct.
So-called accomplishment means it arises spontaneously; this is called Samadhi. If it does not arise spontaneously but requires deliberate mental effort to manifest, that cannot be considered accomplishment; it is not Samadhi. What is called Samadhi is a very deep state of concentration (dhyana), but it does not exclude the simultaneous presence of a state of wisdom. The organic integration of wisdom and meditative concentration is called Samadhi; the absence of either prevents it from being Samadhi. Within this Samadhi, there already exists a relatively deep level of meditative concentration, which necessarily means the manas (the seventh consciousness, or root mind) has also been thoroughly trained. Once the manas is fully trained and capable of functioning at all times, this vision will manifest continuously within the mind.
If your power of concentration (dhyana) has not been perfected, then Samadhi has not been perfected, and the manas has not been successfully conditioned through habituation. It merely indicates that the sixth consciousness (mano-vijnana, or ordinary consciousness) has become more adept. When this adept consciousness applies deliberate effort, it then activates the manas. Only then can the manas engage in deliberate effort, after which the state manifests. Such a state, however, is not stable but intermittent. This level of concentration is insufficient and thus cannot be called Samadhi.
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