Color circle
From Freepedia
A color circle is a way of representing the visible spectrum in a circular form, with colors arranged in sequence around the circumference in order of spectral frequency. Analogous to the use of a color wheel in art, the color circle performs a different purpose, as it is a psychophysical tool used in the exploration of visual perception, its anomalies and optical illusions connected with color vision.
A normal color circle will appear with red at one end of the spectrum and violet at the other, and with a wedge-shaped gap representing colours which have no unique spectral frequency, but are rather formed by the additive mixture of colors from the two ends of the spectrum.
Adding together two colored lights from different parts of the spectrum may produce a third color that appears to match a color in another part of the spectrum, even though the wavelengths involved are quite dissimilar. This type of colour matching is known as metameric matching. Thus a combination of green and red light might produce a color close to amber in apparent hue. The new hue formed lies between the two original colors on the color wheel, but they are usually represented as being joined by a straight line on the wheel, indicating that the resulting hue is less saturated (i.e., paler) than either of the two source colors.
Objects may, of course, be viewed under a variety of different lighting conditions. Our visual system is able to adapt to these different situations by means of a specific feature of the visual system known as chromatic adaptation. This aspect of our visual system is relatively easy to mislead, and as such optical illusions relating to color are a fairly common phenomenon. The color circle is a useful tool in the examination of these illusions.
