I would like to know why certain colors cannot be seen by humans, in an ultra violet and infrared?

this is for my reseach for college.

I would like to know why certain colors cannot be seen by humans, in an ultra violet and infrared?
We don't have the biological mechanisms within our eyes that respond to electromagnetic energy in those wavelengths.



See here for a more indepth discussion:



http://en.wikipedia.org/wiki/Eye
Reply:It's because our genetic make-up has eyes that pick up on the visible part of the spectrum only.Ultra violet(beyond violet) and Infrared(below red)...tom science
Reply:The rods and cones in our eyes aren't adapted to it, because we've never needed to see those colors.



Insects do because that's how they recognize flowers (and in a symbiotic turn, it's how flowers attract the right insects). But we don't suck on flower sperm to keep ourselves alive, we just need to see a lion in the dark (rods), or discern certain animals from the surroundings by color (cones).
Reply:Because the eye does not contain photoreceptors which are sensitive to radiation of these wavelengths. The normal eye has three different photoreceptors sensitive to wavelengths in the range of 400 to 780 nanometers, more or less; one is more sensitive to shorter wavelengths, one to intermediate wavelengths, and one to longer wavelengths. Evolution picked these particular wavelengths because the sun's radiation is maximal for them.
Reply:The retina contains two types of photoreceptors: rods and cones. The rods are more numerous more sensitive to light than cones; however, the eye's color perception comes from the cones. There are approximately 120 million rods and 6-7 million cone photoreceptors.



There are three types of color-sensitive cones in the retina of the human eye, corresponding roughly to red, green, and blue sensitive detectors. Humans don't have UV or IR photodetectors. Why? That is just the way we evolved. Seeing UV or IR was less important than being able to see red, green and blue. UV perception might be more important to insects that need to distinquish among various flowers; and IR reception might be more important to snakes and other animals that hunt burrowing warm-blooded mammals at night.
Reply:very good question. i would like to know that too!
Reply:Is this a math question? Then the answer is because 2+2 = 4.
Reply:If there is no visible light along with IR %26amp; UV rays we would see nothing i.e. it would be pitch black