Does one have perception of the external world while in meditative concentration?

Samādhi can be divided into many levels. Coarse and shallow samādhi is the desire-realm concentration (kāmadhātu-samādhi), in which the mind is somewhat more peaceful, more tranquil, with fewer scattered thoughts and a lighter, more nimble physical body. In this samādhi, the six consciousnesses can still discern the six sense objects; there is still perception and deliberation by the six consciousnesses regarding the six sense objects, and there are still bodily, verbal, and mental actions, so one can still interact with people and handle affairs. In the preparatory concentration (anāgamya-samādhi) of the desire realm, the mind can concentrate on single-pointed deliberation, can achieve freedom from scattered thoughts; the mind is more tranquil and the physical body lighter and more nimble. There is still perception and deliberation by the six consciousnesses regarding the six sense objects, and there are still bodily, verbal, and mental actions, so one can still interact with people and handle affairs. In the first dhyāna of the form realm, the mind is even more tranquil and single-pointed; among the six consciousnesses, the nose consciousness and tongue consciousness are absent, while the remaining four consciousnesses—eye, ear, body, and mind—can still discern the four sense objects, and there is still perception and thought regarding those four sense objects. While abiding in these kinds of samādhi, one can still interact with people and handle affairs, with mild afflictions and swift deliberation. In samādhi of the second dhyāna and above, one cannot interact with people and handle affairs, because the five sense consciousnesses are gone: the body cannot move, one cannot discern form, sound, smell, taste, or touch, and there can be no bodily or verbal actions.

During cultivation, when meditative concentration manifests, the mind's functions are developed and expanded, and the obstruction of the aggregate of form (rūpa) becomes smaller. Originally, with the eyes closed, there was darkness before one's eyes; now, even with the eyes closed, one can see the light before one. In fact, whether the eyes are closed or open, asleep or awake, the tathāgatagarbha always transmits material sense objects through the eye faculty; it only depends on how capable the conscious mind is at discrimination, and whether it is obstructed by the aggregate of form. Even while asleep, external material sense objects continue to be transmitted to the supreme faculty (rūpa-prasāda). For example, sometimes in the morning we are awakened by intense stimulation from sunlight; this is because first there are the material sense objects and mental sense objects in the supreme faculty, and afterward the eye consciousness and mind consciousness are born, and so we wake up. When sitting in meditation with samādhi present, there is not darkness before the eyes but rather a certain degree of light; as for what kind of light it is and how bright it is, that depends on the depth of one's meditative concentration.