In total darkness what we perceive is a uniform gray that in the nineteenth century received the name eigengrau, from the German intrinsic gray, and that today is called "visual noise" . This means that we see total darkness with more light than a black object in normal light conditions or the night sky, due to the contrast provided by the stars.
This is due to a peculiar process that happens in the photosensitive cells of our retina, the rods and cones. Random events occur throughout the day that are indistinguishable from those caused by photons of light when they hit the retina.
In human rods, these random "flashes" occur once every 100 seconds, providing noticeable background "visual noise" in completely dark conditions. Moreover, in experiments with toads it has been found that these events depend on temperature , which makes scientists suspect that the molecule behind this phenomenon is rhodopsin , a photosensitive protein composed of two parts, opsin and Vitamin A. Rhodopsin, found in rods – the cells that allow us to have night vision – is very unstable and can spontaneously lose its integrity and cause the eye to send signals to the brain that a photon of light has arrived when, in fact, that has not happened.
