My train of thought goes like this. When sufficient pressure is applied to the eyes your cones and or rods are stimulated and you see "light". It's not "photonic light" it's just your brains reaction to the stimulation. I've seen what I would call "luminescent phenomenon" that seems to be a complex version of this happening to the point of actually clearly looking like things. Picture an old 16 bit video game to get a basic sense of it. I would speculate that maybe some apparitions and/or U.F.O.s might be the result of something stimulating the cones and rods directly. It doesn't have to be paranormal in nature or even some kind of intentional manipulation.
I have no clue how to test that without actually doing harm to someone's eyes.