Many people are able to perceive polarization of light. It may be seen as a yellowish horizontal bar or bow-tie shape (with “fuzzy” ends, hence the name “brush”) visible in the center of the visual field against the blue sky viewed while facing away from the sun, or on any bright background.

Eigengrau (German: “intrinsic gray”), also called Eigenlicht (“intrinsic light”), dark light, or brain gray, is the color seen by the eye in perfect darkness. Even in the absence of light, some action potentials are still sent along the optic nerve, causing the sensation of a uniform dark gray color. Eigengrau is perceived as lighter than a black object in normal lighting conditions, because contrast is more important to the visual system than absolute brightness.

The Ganzfeld effect (from German for “complete field”) is a phenomenon of visual perception caused by staring at an undifferentiated and uniform field of color. The effect is described as the loss of vision as the brain cuts off the unchanging signal from the eyes. The result is “seeing black” - apparent blindness.

The Prisoner’s Cinema is a phenomenon reported by prisoners confined to dark cells and by others kept in darkness, voluntarily or not, for long periods of time. […] The “cinema” consists of a “light show” of various colors that appear out of the darkness. The light has a form, but those that have seen it find it difficult to describe. Sometimes, the cinema lights resolve into human or other figures

A phosphene is a phenomenon characterized by the experience of seeing light without light actually entering the eye.