Why does everything look grey in the dark?

1the puzzle

Ever notice at night, in dim moonlight, colors vanish and everything looks grey? That's not your imagination — your eye actually switches modes.

2two sensors

Your retina, the screen at the back of your eye, has two kinds of light sensors: cones for color, and rods for dim light.

3cones: color

Cones need bright light and come in three types, tuned to red, green, and blue — mixing their signals is literally how you see color.

4rods: grey

Rods are far more sensitive — over a hundred times — but they come in only one flavor, so they can't tell hues apart at all, just brightness.

5the switch

So at dusk, as light fades, your cones shut down and rods take over — the world quietly shifts from full color to black and white, right inside your own eye.