(Greek: light)

The term phos- is rarely used in any dictionaries (as shown below); however, this phospho- unit will present the most relevant use of this Greek element.

phosphene (s) (noun), phosphenes (pl)
1. A sensation of seeing light caused by pressure or electrical stimulation of the eye: "A phosphene is an entoptic phenomenon (visual effect whose source is within the eye) characterized by the sensation of light from mechanical, electrical, or magnetic stimulation of the eye's retina, or from random firing of cells in the visual system, rather than from light."
2. Sensations of light caused by excitations of the retina by mechanical or electrical means rather than by light, as when the eyeballs are pressed through closed lids: "The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes."