American Flag Optical Illusion – SICK Science

With a little staring, a strangely colorful optical illusion resolves into the Stars and Stripes.

At first, your eyes are working just fine and the image your brain produces for you is correct even though you may wonder a little bit. All you have to do is get a little closer to the screen, stare at the white dot in the center of the image for 20 seconds or so, and then feel good about what happens next. You’re taking advantage of some optical chemistry and neurological confusion to generate an image of the good, old Red, White, and Blue.

SICK Science® is a registered trademark of Steve Spangler, Inc. All Rights Reserved.

Experiment Materials

  • Your Eyes
  • This Video

Experiment Videos

Experiment

1

Your task: focus on the white dot in the center of the image. It might be useful to have someone manage the mouse for you and click away any pop-ups that come up on the screen. You can do it yourself but don’t get too distracted. Keep staring!

2

Your focus remains fixed on that white dot and nothing else. You may feel like you’re getting tunnel vision as your peripheral vision gets a little fuzzy. About all you can see is that white dot.

3

After 20 seconds or so, the strange color combination disappears and is instantly replaced with the familiar red, white, and blue of the US flag. It’s kind of a relief, actually.

How Does It Work

The back of your eye is layered with special cells that respond to light. There are two kinds of these “photoreceptors” (light receivers) and they’re called rods and cones because of their shapes. It’s estimated that there are 120 million rod cells and a paltry 6-7 million cone cells in each of your eyes. Rods are more sensitive to light and dark changes so you use them more at night or in a dark space. Cones respond better in bright light to wavelengths of color so they work mostly during the daytime. Amazingly, like a TV or computer screen, there are three types of cone cells that are red-, green-, and blue-light sensitive. Your perception of colors comes from how these cells fire together and send the messages to your brain for interpretation.

When you stare at a color for a long time, the cones detecting that color get tired or fatigued and your eyes become less responsive to that color of light. After several seconds of staring and then looking away at a white surface, what you see is an afterimage that results from the photoreceptors not being balanced. The cells temporarily “subtract” cyan, black, and yellow light from the white light coming off the white page. The colors of the US flag occur because red, white, and blue are the complementary colors of cyan, black, and yellow light. After a few seconds, chemical balance is restored in the cells and the afterimage fades away.

Take It Further

For additional optical illusions in the Spangler file, check out the Heart Optical Illusion or the Growing and Shrinking Head Optical Illusion.