When you look directly at a bright light, why does it “stain” (for lack of a better term) your vision when you look away?

Question

When you look directly at a bright light, why does it “stain” (for lack of a better term) your vision when you look away?

In: Biology

Answer 1

Disclaimer: not a scientist, just some dude with a vague interest in biochemistry.

At the heart of the cells in your eyes that receive light from the world and produce a signal to the nerves is a chemical (similar to betacarotene) that’s continuously reacting back and forth between two forms. This is a dynamic equilibrium, where the relative concentration of both of these chemicals changes when exposed to light.

When you stare into a light for a long time, you heavily skew the equilibrium towards charged molecules, and it takes some time for the signal to revert back to its baseline.