Actually…

we do know that some saints were endowed with characteristics proper of a glorified body, one of which is the “halo”. Now that was not granted to all, nor necessarily visible, but we do know of souls who were granted by God the possibility, for their own good, of seeing this phenomenon when at the presence of someone who would later be canonized.
I have two witnesses in mind (luckily I could quickly find the book and locate the exact paragraph

)…one is Mother Ana de San Alberto, prioress, of who was assisting a Holy Mass by St. John of the Cross and saw Him surrounded by a great light as he took a rather long time for the celebration. Later in confession, she asked him why he was taking longer than usual, and when he tried not to answer, she said: “What if I were to tell you why you were taking so long?” to which St. John, surprised, asked: “Did you see something? How long did I take?” and she told her what she had seen and replied: “No time is long enough to experience the heavenly goods.” Several witnesses saw light come out from the confessional when he was in (in other occasions, I mean), and when one of them told St. John privately, he replied: “Be quiet, silly man, and don’t tell anyone!” These witnesses are taken from the reputable book “Vida y Obras de San Juan de la Cruz” by Crisogono de Jesus O.C.D.
This is one example, but of course it is not the only one. And we also know notoriously of Moses having this visible characteristic.
So while pious painters may have emphasized this characteristic by depicting all saints with such visible halos around their heads while in reality they looked like ordinary people, they were not deceiving you, for at least mystically they did have a special characteristic invisible to the human eye.
This same example of “visible light radiance” can be made with regards to the Holy Eucharist: no doubt, the host has (and is meant to have) the look of ordinary bread, however we read in the lives of many saints that at one time or another they did see the Eucharist radiate light, as for ex. represented in
this beautiful painting.