When a human “sees” a color, light first enters the eye through the cornea. The lens and the pupil help to focus the light and control the amount that can enter. When the focused light hits the back of the eye, the retina converts the light energy into biochemical signals, which are sent to be processed by the brain.
This conversion of light energy to biochemical energy is performed by two types of photoreceptors: cones and rods. These cells, located within the retina, play crucial roles in how we perceive our surroundings. Rods are responsible for vision at low light levels (scotopic vision), while cones are active at higher light levels (photopic vision) and enable us to see color.
Cones Are the Basis of Color Vision
Cones, numbering around 6 million in each eye, are concentrated mainly in the fovea, the central area of the retina. There are three types of cones, each sensitive to different wavelengths of light: long (red), medium (green), and short (blue). This diversity in sensitivity allows for the perception of a wide range of colors through the combination of signals from these photoreceptors.
Rods Navigate Low Light Conditions
Rods outnumber cones significantly, with about 120 million rods in the human eye. They are highly sensitive to light but do not discern color. Instead, rods detect shades of gray and are vital for night vision and peripheral vision. Their high sensitivity to light makes them essential in dark environments, where they enable us to detect shapes and movements.
How Rods and Cones Work Together
Rods and cones work together to help us detect both intensity of light and the color. The shift between rod and cone dominance enables humans to see across a wide range of lighting conditions. In bright environments, cones provide detailed color information. In darker settings, rods take over, allowing for continued vision though in a more monochromatic sense. This functional differentiation and cooperation between rods and cones are fundamental for the adaptability of human vision in different lighting scenarios.
Sometimes, there can be a deficiency in the short (S), medium (M), and/or long (L) cones and it can cause color vision disorders such as color blindness. Depending on which photoreceptors are affected, color perception can be affected differently. The example below shows the normal range of human color vision compared to the color range of someone who has a deficiency in either their short, medium, or long wavelength photoreceptors.
Color Perception Varies from Person to Person
Everyone experiences color differently. Natural variations in the density and distribution of rods and cones, genetic conditions like colorblindness shown above, your age or medications you’re taking, differences in brain chemistry, and a number of other factors, means that not everyone will perceive color in the same way.
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