The Muser
Physics & Physiology of Color
All the material located at this web page address is
J. C. Adamson, 2008 and prior years, unless otherwise noted.

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A Visual Effect Using Complementary Colors


To observe this phenomenon, stare intently for about one minute at the lower-right star in the oddly colored flag. Don't look anywhere else on the screen, or anywhere else in the room during that minute. Then switch your gaze to the single star in the white field next to the flag.  Do that now.

The effect is caused by desensitization, or fatigue, of the cone cells in your retina, and it demonstrates complementary colors. As you stare at the flag image, the cone cells in part of your retina are being stimulated by yellow light, which is composed of red and green light. In time, those cells become less sensitive to the red and green. When you shift your gaze to the white field, your eyes are stimulated by roughly equal amounts of red, green, and blue light. The cone cells that have been desensitized to red and green are relatively more sensitive to the remaining blue light, and they respond as if they were seeing more blue light than other colors.

To state the idea differently, the eye becomes desensitized to one color, then responds more to the complement of that color.

Of course, the same thing happens where you've been seeing cyan (blue + green) light. The retina becomes relatively more sensitive to red light in those areas. Where you've been seeing black, no desensitization occurs, and you later see white light in its full strength.

This fatigue effect is also a test for complementary colors . Try a fatigue experiment with brightly colored red and green pieces of paper. You'll see that magenta is always the complement of green, and cyan is always the complement of red.

© J. C. Adamson, 1997