Objection 1. It would seem that the clarity of the glorified body is invisible to the non-glorified eye. For the visible object should be proportionate to the sight. But a non-glorified eye is not proportionate to see the clarity of glory, since this differs generically from the clarity of nature. Therefore the clarity of the glorified body will not be seen by a non-glorified eye.
Objection 2. Further, the clarity of the glorified body will be greater than the clarity of the sun is now, since the clarity of the sun also will then be greater than it is now, according to Isaiah 30:26, and the clarity of the glorified body will be much greater still, for which reason the sun and the entire world will receive greater clarity. Now a non-glorified eye is unable to gaze on the very orb of the sun on account of the greatness of its clarity. Therefore still less will it be able to gaze on the clarity of a glorified body.
Objection 3. Further, a visible object that is opposite the eyes of the seer must needs be seen, unless there be some lesion to the eye. But the clarity of a glorified body that is opposite to non-glorified eyes is not necessarily seen by them: which is evident in the case of the disciples who saw our Lord's body after the resurrection, without witnessing its clarity. Therefore this clarity will be invisible to a non-glorified eye.
On the contrary, A gloss on Philippians 3:21, "Made like to the body of His glory," says: "It will be like the clarity which He had in the Transfiguration." Now this clarity was seen by the non-glorified eyes of the disciples. Therefore the clarity of the glorified body will be visible to non-glorified eyes also.
Further, the wicked will be tortured in the judgment by seeing the glory of the just, according to Wisdom 5:2. But they would not fully see their glory unless they gazed on their clarity. Therefore, etc.
I answer that, Some have asserted that the clarity of the glorified body will not be visible to the non-glorified eye, except by a miracle. But this is impossible, unless this clarity were so named equivocally, because light by its essence has a natural tendency to move the sight, and sight by its essence has a natural tendency to perceive light, even as the true is in relation to the intellect, and the good to the appetite. Wherefore if there were a sight altogether incapable of perceiving a light, either this sight is so named equivocally, or else this light is. This cannot be said in the point at issue, because then nothing would be made known to us when we are told that the glorified bodies will be lightsome: even so a person who says that a dog [The dog star] is in the heavens conveys no knowledge to one who knows no other dog than the animal. Hence we must say that the clarity of a glorified body is naturally visible to the non-glorified eye.
Reply to Objection 1. The clarity of glory will differ generically from the clarity of nature, as to its cause, but not as to its species. Hence just as the clarity of nature is, by reason of its species, proportionate to the sight, so too will the clarity of glory be.
Reply to Objection 2. Just as a glorified body is not passible to a passion of nature but only to a passion of the soul [Cf. 82, 1], so in virtue of its property of glory it acts only by the action of the soul. Now intense clarity does not disturb the sight, in so far as it acts by the action of the soul, for thus it rather gives delight, but it disturbs it in so far as it acts by the action of nature by heating and destroying the organ of sight, and by scattering the spirits* asunder. ["Animalem," as though it were derived from "animus"--the mind. Cf. I-II, 50, 1,3m; I-II, 52, 1,3m.] Hence, though the clarity of a glorified body surpasses the clarity of the sun, it does not by its nature disturb the sight but soothes it: wherefore this clarity is compared to the jasper-stone (Apocalypse 21:11).
Reply to Objection 3. The clarity of the glorified body results from the merit of the will and therefore will be subject to the will, so as to be seen or not seen according to its command. Therefore it will be in the power of the glorified body to show forth its clarity or to hide it: and this was the opinion of Praepositivus.
Source: Summa Theologica (New Advent)