For the majority of people, colors are a natural part of their daily lives. But why can we see colors at all, and how does it work? Dogs, cats or bulls can’t, and obviously still find their way in the world quite well. The fact that we can recognize and distinguish colors gives us a whole series of advantages that make the survival of our evolutionary ancestors in the wild, as well as our orientation in modern civilization, considerably easier and safer. The process of color vision itself and the fact why we can determine with certainty what color exactly an object has is quite an elaborate process.
Color is not created in the eye, but in the brain
First of all, it must be stated that our eyes are not superior in physical optical terms. The image of our surroundings projected onto the retina is not of particularly good quality: it is distorted spatially and in terms of color, quite blurry and also upside down. Only the brain reconstructs from the information of the eyes with the help of biochemical processes and with inclusion of further stored information a picture of our environment, as we are used to it and in which we can move safely. Incidentally, this also means that the color image we perceive is created with the help of our stored knowledge, our experience, our interests and, not least, our personal mood and state of mind. This also makes it clear why two people see the same thing at the same moment, but are very likely to perceive it differently.
Cones and rods
Our eyes provide more information than just the projection onto the retina, which is crucial to the creation of a colorful image. Electromagnetic radiation, in the form of light of different wavelengths, hits our eyes and passes through the cornea, iris, pupil, lens and vitreous body until it reaches the retina. There are two different types of photoreceptors on the side of the retina that is not exposed to light. These are once about 120 million so-called rods and ca. 6 million cones. The rods are very sensitive to light and are responsible for light/dark vision, while the less light-sensitive cones are responsible for color vision.
The brain as a color mixing apparatus
Three different types of cones (L, M, and S) each absorb a specific wavelength range of light. Here, the so-called "long cones" perceive the area that our brain subsequently interprets as red, while the medium or. Short cones register the proportion of green and blue. They owe their specific sensitivity to the respective spectral range to certain pigments that change their molecular structure when exposed to light. They trigger signals that the sensory cell transmits in the form of an impulse to a ganglion cell of the nervous system. This receives the signals of the different cone types and computes them against each other. From this information with the respective proportions of the three basic color information, our brain can determine the exact mixture and thus the correct color tone. The information from the rods, on the other hand, is needed by our brain to recognize spatial depth and contrasts by means of the black and white components of the light. Since they are very sensitive to light, they allow us to orient ourselves even in low light conditions. When it is dark, they do most of the work, the cones are then no longer active. This is the reason why we do not see colors in the dark.
Different colors from different light
The crucial prerequisite for being able to see colors is light. And in our eyes, objects get their color by either absorbing or reflecting light of different long wavelengths. Basically, the color impression is created by the property of the surface of an object to reflect certain parts of the light more strongly than others. Water, for example, appears blue to us because the red, yellow and green components of sunlight are absorbed very quickly and the blue component is reflected most strongly. If you change the color or. wavelength of light, for example, filters also change the color of the illuminated object. Thus, a red apple suddenly appears black in green light.
A goldfish sees more
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