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What is it about the human eye that limits the types of wavelengths in the electromagnetic spectrum that can be seen as visible light? Why are other animals capable of interpreting infrared waves as well?
The back of the eye is covered by the retina which contains millions of cells called photoreceptors that absorb light. The brain receives electrical signals from all of these cells and compiles them into an image. The photoreceptors in the retina which are responsible for color vision are called cones. In humans, there are three different types of cones, each of which absorbs either red, green or blue light. Other colors are interpreted by the brain as a combination of these three primary colors.
Light can be described as a wave and the distance between the peaks of the wave, called the wavelength, is what determines a wave`s color. The cones in your eye contain a pigment whose molecules are made of two smaller pieces called retinal and opsin that change shape from bent to straight when it absorbs energy from a light wave. The change in structure frees the opsin which C R E A T Es a chain reaction of biochemical processes that cause an electrical signal to be sent to the brain. Retinal by itself absorbs only green light, but when it is linked with an opsin the combined structure absorbs a different color. Light waves with either too high or too low of a wavelength do not cause this reaction to take place and so are not detected by the eye.
Different species of animals have pigments that contain the same retinal but different opsins. Changes in the combined molecule due to different opsins tunes the absorbance of the pigment making it more sensitive to different wavelengths. Some animals even have more than three types of cones. This will allow them to detect different wavelengths of light than humans.
Link:
http://www.ccmr.cornell.edu/education/ask/index.html?quid=800
/Zeta
2007-01-08 23:13
(direct link)
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