Eigengrau

These terms arise due to the perception of an ever-changing field of tiny black and white dots seen in the phenomenon.

[2][3] 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.

Contrast threshold data, collected by Blackwell[5] and plotted by Crumey, shows Eigengrau occurring at adaptation luminances below approximately 10− 5 cd m−2 (25.08 mag arcsec−2).

Researchers noticed as early as 1860 that the shape of intensity-sensitivity curves could be explained by assuming that an intrinsic source of noise in the retina produces random events indistinguishable from those triggered by real photons.

[7][8] Later experiments on rod cells of cane toads (Rhinella marina) showed that the frequency of these spontaneous events is strongly temperature-dependent, which implies that they are caused by the thermal isomerization of rhodopsin.