Afterimage

vision · eyes · optical illusion · science

Your eyes keep glowing. When light hits the back of your eye, special cells called photoreceptors get excited and create a signal to your brain. Even after the light is gone, these cells keep buzzing for a moment, so you still see the image.

Stare at the sun... carefully. If you stare at a bright light for a few seconds (safely, through special glasses), then close your eyes or look at something dark, you'll see a ghostly dark spot floating there. That's an afterimage, and it fades as your eye cells calm down.

Colors can flip. Sometimes afterimages show up in opposite colors, like seeing cyan when you looked at red, or yellow when you looked at blue. Your brain tries to balance out the colors it just saw.

It happens in seconds. An afterimage usually disappears within a few seconds to a minute, as your photoreceptors settle back down and stop firing. It's a totally normal part of how your eyes work.

Normal or unusual. Most afterimages are just your eyes doing their job, but very long-lasting ones can sometimes be a sign of an eye problem that needs a doctor's attention.