Several people cluster around the bed of a dying person. The pupils of the dying person widen as their condition worsens. And as the pupils of the dying person widen, they notice that the lighting in the room becomes brighter, or even that the room is bathed in bright light. No-one else notices that the lighting in the room has changed, only the dying person, because only the pupils of the dying person widen. This is why dying people may say they see bright light, bright light that does not hurt the eyes, or even bright landscapes. . . .

The reduced focal depth of the eyes of a person with wide open pupils, means they see all people, and objects upon which they do not focus their eyes, as vague and blurred forms. Furthermore, more light enters the eyes of a person with wide open pupils, so they perceive people upon which their eyes are not focussed as vague blurred bright figures, or even as beings of light. The mental function of the dying and nearly-dead is abnormal, so they may interpret these bright forms and figures as being supernatural, ethereal, other-worldy beings of light, or even as personages and gods from their religion.

—Dr. G.M. Woerlee, from Mortal Minds: The Biology of Near-Death Experiences, 2003.