Light travels into the eye to the retina, located on the back of the eye. The retina is covered with millions of light receptive cells called rods and cones. When these cells detect light, they send signals to the brain. Most people have three kinds of cone cells, and every color stimulates more than one cone. Their combined response produces a unique signal for each color, and millions of different colors can be distinguished this way. These cells, working in combination with connecting nerve cells, give the brain enough information to interpret and name colors.
Considered to be part of the brain itself, the retina is covered by millions of light-sensitive cells, some shaped like rods and some like cones.
These receptors process the light into nerve impulses and pass them along to the cortex of the brain via the optic nerve. Have you ever wondered why your peripheral vision is less sharp and colorful than your front-on vision? It's because of the rods and cones. Rods are most highly concentrated around the edge of the retina. There are over million of them in each eye.
Rods transmit mostly black and white information to the brain. As rods are more sensitive to dim light than cones, you lose most color vision in dusky light and your peripheral vision is less colorful. It is the rods that help your eyes adjust when you enter a darkened room.
Cones are concentrated in the middle of the retina, with fewer on the periphery. Six million cones in each eye transmit the higher levels of light intensity that create the sensation of color and visual sharpness. There are three types of cone-shaped cells, each sensitive to the long, medium or short wavelengths of light.
This mixture is known as white light. When white light strikes a white object, it appears white to us because it absorbs no color and reflects all color equally. Each type of cone is sensitive to different wavelengths of visible light.
The cones then send a signal along the optic nerve to the visual cortex of the brain. The brain processes the number of cones that were activated and the strength of their signal.
After the nerve impulses are processed, you see a color— in this case, yellow. Your past visual experiences with objects also influence your perception of color. This phenomenon is known as color constancy. Color constancy ensures that the perceived color of an object stays about the same when seen in different conditions.
For example, if you looked at a lemon under a red light, you likely would still perceive the lemon to be yellow. Color blindness can occur when one or more of the cone types are not functioning as expected. Cones can be absent, nonfunctioning or detect a different color than normal.
Red-green color blindness is the most common, followed by blue-yellow color blindness. Men are more likely to have color blindness than women. Scientists are currently developing new treatments for color blindness. Researchers estimate that up to 12 percent of females have four cone types in their retinas, rather than three. These individuals have the potential to perceive times more colors than the rest of us. Such chemicals that are capable of selectively absorbing one or more frequency of white light are known as pigments.
In Example A, the pigment in the sheet of paper is capable of absorbing red, orange, yellow, blue, indigo and violet.
In Example B, the pigment in the sheet of paper is capable of absorbing orange, yellow, green, blue, indigo and violet. In each case, whatever color is not absorbed is reflected. Check your understanding of these principles by determining which color s of light are reflected by the paper and what color the paper will appear to an observer.
See Answer Example A: Green will be reflected and so the paper appears green to an observer. Express your understanding of this principle by filling in the blanks in the following diagrams.
See Answer Example A: Green will be transmitted and so the object appears green to an observer. Example B: Both green and blue will be transmitted and so the object appears greenish-blue to an observer.
The colors perceived of objects are the results of interactions between the various frequencies of visible light waves and the atoms of the materials that objects are made of. Many objects contain atoms capable of either selectively absorbing, reflecting or transmitting one or more frequencies of light.
The frequencies of light that become transmitted or reflected to our eyes will contribute to the color that we perceive. Natural philosophers have long pondered the underlying reasons for color in nature. One common historical belief was that colored objects in nature produce small particles perhaps light particles that subsequently reach our eyes.
Different objects produce different colored particles, thus contributing to their different appearance. Is this belief accurate or not? This view presumes that the appearance of an object is independent of the colors of light which illuminate the object.
We observe that the same object appears different colors when viewed under different light. So the secret to an object's appearance is not strictly due to its ability to produce a color. In fact the object's only role in determining its appearance is in its ability to absorb certain wavelengths of light which shine upon it.
What color does a red shirt appear when the room lights are turned off and the room is entirely dark? When the room lights are turned off there is no light , any object present in the room appears black. The color appearance of an object depends upon the light which that objects reflects to the observer's eye. Without any incident light, there can be no reflected light. Such an object appears black - the absence of light. In each case, determine which color s of light are reflected by the paper and what color the paper will appear to an observer.
See Answer Practice A: No light will be reflected; it is all absorbed. Thus, the paper would appear black to an observer. Practice B: Red and orange will be reflected and so the paper appears reddish-orange to an observer. Express your understanding of this principle by determining which color s of light will be transmitted and the color that the paper will appear to an observer.
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