The Light That Isn’t There
In total darkness, many people report seeing a uniform dark gray field. This phenomenon, called Eigengrau—from German, meaning “intrinsic gray”—is not produced by light, but by internal processes in the eye. It’s a constant, ever-present backdrop even when no light enters the eyes.
Not True Black
Though Eigengrau appears dark, it’s perceived as lighter than a truly black object under normal lighting. This is because the human visual system is more sensitive to contrast than to absolute brightness. The night sky, dotted with stars, often looks darker than Eigengrau due to these contrast effects.
A Signal from Within
In 1860, researchers proposed that the eye itself produces signals indistinguishable from light. Modern experiments confirmed that thermal isomerization of rhodopsin, a light-sensitive protein in rod cells, triggers these false signals—sometimes just once every 100 seconds.
Lasting for Centuries
Calculations suggest that a single rhodopsin molecule in a rod cell might spontaneously activate only once every 420 years on average. This rarity still adds enough visual “noise” to generate the gray field we see in the absence of light.
In complete darkness, many people still see a soft gray glow.
Known as Eigengrau, or 'intrinsic gray,' this visual experience doesn’t come from outside light—it’s generated inside the eye itself through spontaneous activity in light-sensitive cells.🧵👇 pic.twitter.com/TDIOvcIYpc
— Detective Tiger's Stories (@TigerDetective) April 16, 2025