The word phosphene is derived from two Greek words phos which means light and phainein which means to show. Phosphene is a phenomenon that causes an experience of seeing light without light. This experience is caused usually when the eyeballs are rubbed with eyes closed. This phenomenon is usually linked with optic neuritis and is persuaded by movement or sound.  Those who lack visual stimulation and those who are under heavy dosed medication or highly addicted to drugs may experience this sensation.