How Do We See Color?
Stephanie Pappas, Live Science
"Roses are red and violets are blue, but we only know that thanks to specialized cells in our eyes called cones. When light hits an object – say, a banana – the object absorbs some of the light and reflects the rest of it. Which wavelengths are reflected or absorbed depends on the properties of the object.
For a ripe banana, wavelengths of about 570 to 580 nanometers bounce back. These are the wavelengths of yellow light. When you look at a banana, the wavelengths of reflected light determine what color you see. The light waves reflect off the banana's peel and hit the light-sensitive retina at the back of your eye. That's where cones come in.
Cones are one type of photoreceptor, the tiny cells in the retina that respond to light. Most of us have 6 to 7 million cones, and almost all of them are concentrated on a 0.3 millimeter spot on the retina called the fovea centralis."
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3 comments:
One of the interesting things about color vision is that most mammals actually have very poor color vision or no color vision at all. Primates (the sub-group of mammals to which humans belong) have evolved better color vision, probably because they're largely fruit-eaters and color vision is useful for distinguishing things like bananas from their surroundings. But our color vision (and vision generally) is still much inferior to that of birds and reptiles. It's actually turtles and tortoises that have the best color vision in the world, with more different kinds of receptor cells in their retinas than we have.
This is understandable when one remembers that all mammals are descended from small shrew-like animals which, for tens of millions of years during the age of dinosaurs, were probably nocturnal or living underground -- ways of life for which color vision is not very useful. But one wonders how creationists account for God giving man, the supposed crown of creation, vision far inferior to that of the bird or the lowly turtle.
Pretty neat..and we take it for granted. There are exceptions
(about 250 million, world wide)
when specific cone arrays fail to function-
"The exact physical causes of color blindness are still being researched but it is believed that color blindness is usually caused by faulty cones but sometimes by a fault in the pathway from the cone to the brain.
People with normal color vision have all three types of cone/pathway working correctly but color blindness occurs when one or more of the cone types are faulty. For example, if the red cone is faulty you won’t be able to see colors containing red clearly. Most people with color blindness can’t distinguish certain shades of red and green."
-a defect carried on the x chromosome, sort of a guy thing.
Infidel753, thanks for your information on why we higher mammals have poorer sight than do turtles and birds.
The creature that has the widest range of color, from infrared to ultraviolet, is the stomatopod, othrwise known as the mantis shrimp, a creature I've always been fascinated with.
"The mantis shrimp has one of the most elaborate visual systems ever discovered.
The midband region of its eye is made up of six rows of specialised ommatidia. Four rows carry up to 16 different photoreceptor pigments, 12 for colour sensitivity, others for colour filtering. The vision of the mantis shrimp is so precise that it can perceive both polarised light and multispectral images.
Their eyes (both mounted on mobile stalks and capable of moving independently of each other) are similarly variably coloured and are considered to be the most complex eyes in the animal kingdom."
BB-Idaho, in our family, we three sisters carry the gene for color blindness. Our father was color blind and each of us have a son with color blindness, which is passed on through the mother. There is a 50/50 chance of passing it on. I had one son, he's color blind, my oldest sister had one son, he's color blind, our middle sister had two sons, one is color blind.
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