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Color Vision

Human color perception is dependent on three conditions. First, whether we have normal color vision; second, whether an object reflects or absorbs light; and third, whether the source of light transmits wavelengths within the visible spectrum. Rods contain only one pigment which is sensitive to very dim light, and which facilitates night vision but not color. Cones are activated by bright light and allow us to see colors and fine detail. There are three types of cones that contain different pigments which absorbs wavelengths in the short (S), middle (M), or long (L) ranges. Cones are often labeled blue, green, and red, because they detect wavelengths in those color spectrums. The peak wavelength absorption of the S (blue) cone is approximately 430 nm; the M (green) cone 530 nm; and the L (red) cone 560 nm.

The range of detectable wavelengths for all three types of cones overlap, and two of them—the L and M cones—respond to all wavelengths in the visible spectrum. Most of the light we see consists of a mixture of all visible wavelengths which results in "white" light, like that of sunshine. However, cone overlap and the amount of stimulation they receive from varying wavelengths produces a fabulous range of vivid colors and gentle hues present in normal color vision. Approximately 8% of all human males experience abnormal color vision, or color blindness.

Actually, we do not "see" colors at all. A leaf, for example, appears green because it absorbs long- and short-wavelengths but reflects those in the middle (green) range, stimulating the M cones to transmit electrochemical messages to the brain which interprets the signals as the color green.

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