How Eyes Perceive Color
Objects do not possess color of their own. Our eyes perceive color as different wavelengths of light that bounce off things, and our brains process that information to help us interpret the world we see in vibrant color.
The visible spectrum lands between ultraviolet light and red light for humans, but scientists believe that humans can recognize up to 10 million colors.
The process for color recognition is that light hits an object; that object absorbs some of the light, and then that same object reflects the rest of the light. The light wavelengths that absorb or reflect are based on the object’s properties. The portion of the light spectrum that humans perceive is the reflected light, which enters the eye through the cornea then bends the light toward the pupil, finally focusing on the light-sensitive retina.
For example, light wavelengths that reflect to the eye take about 570 to 580 nanometers to bounce back into the eye for a lemon. And these light wavelengths are considered yellow light.
Within the eye’s retina, one type of photoreceptor is a cone. Most humans have 6-7 million cones, and they are concentrated on a 0.3-millimeter spot called the fovea centralis in the retina. Nearly 64% of the cones respond strongly to red light, while a little less than a third react to green light. The final 2% or so of cones fire in response to blue light.
Three cone types in the eye mean that humans are better than most mammals at perceiving color in the world. However, other animals are even better at color vision, specifically birds and fish! Birds and fish have four types of cones, which allow them to see ultraviolet light. This wavelength is shorter than what the human eye can see.
Meanwhile, another type of cell is at work in color perception, and that cell is called a rod. Rods activate in dim or low light. Most humans have approximately 110 million rods. In darker environments, light is still reflecting; however, your eyes will only be able to view objects through the rods’ activation, which show shades of gray.
Another phenomenon is color constancy. When you are familiar with an object being a particular color, your brain will continue to recognize the object as being that color even if it’s viewed in different conditions. For example, if you place a lemon under a red light, your brain will still likely perceive the lemon as yellow.
Color Vision Anomalies
When cones or rods are not functioning as they usually do, humans can perceive colors differently – most often, this is termed color blindness. Color blindness occurs when cones are absent or detecting a different color than normal. The most common color blindness is red-green blindness, followed by blue-yellow blindness. In general, men experience more color blindness than women.
Color plays an integral role in how humans interact with different objects. For example, we use color to recognize ripe fruit, and colors also signal when to stop or go.
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