Eigengrau

Eigengrau (German for "intrinsic gray"; pronounced [ˈʔaɪ̯gŋ̍ˌgʁaʊ̯] ^ⓘ), also called Eigenlicht (Dutch and German for "intrinsic light"), dark light, or brain gray, is the uniform dark gray background color that many people report seeing in the absence of light. The term Eigenlicht dates back to the nineteenth century,^[1] and has rarely been used in recent scientific publications. Common scientific terms for the phenomenon include "visual noise" or "background adaptation". These terms arise due to the perception of an ever-changing field of tiny black and white dots seen in the phenomenon.^[2]

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.^[3] For example, the night sky looks darker than Eigengrau because of the contrast provided by the stars.

Contrast threshold data, collected by Blackwell^[4] and plotted by Crumey, shows Eigengrau occurring at adaptation luminances below approximately 10^{− 5} cd m⁻² (25.08 mag arcsec⁻²).^[5] This is a limiting case of Ricco's law.