Eigengrau (
German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ger ...
for "intrinsic gray"; ), 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, but 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.
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. For example, the night sky looks darker than Eigengrau because of the contrast provided by the stars.
Cause
Researchers noticed early on 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. Later experiments on
rod cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in per ...
s 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
Rhodopsin, also known as visual purple, is a protein encoded by the RHO gene and a G-protein-coupled receptor (GPCR). It is the opsin of the rod cells in the retina and a light-sensitive receptor protein that triggers visual phototransduction ...
. In human rod cells, these events occur about once every 100 seconds on average, which, taking into account the number of rhodopsin molecules in a rod cell, implies that the
half-life of a rhodopsin molecule is about 420 years. The indistinguishability of dark events from photon responses supports this explanation, because rhodopsin is at the input of the
transduction chain. On the other hand, processes such as the spontaneous release of
neurotransmitter
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell.
Neuro ...
s cannot be completely ruled out.
See also
*
Closed-eye hallucination
*
Impossible color
Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of perceiving for one reason or another, and fictional colors are rou ...
*
Visual snow
References
{{Authority control
Color
Darkness
Shades of gray
Vision