Color is a complex phenomenon that involves both physics and perception. The colors we see depend on the light that illuminates objects and how that light is reflected and absorbed. But color is also a sensation that is created in our brains. So while physics determines the makeup of light and the interactions between light and matter, our visual systems determine how that information gets translated into the colors we experience.
The Physics of Color
On a fundamental level, color originates from light. Visible light is part of the electromagnetic spectrum that includes radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays. Visible light is composed of different wavelengths that our eyes perceive as different colors.
The wavelength of light determines its color. Shorter wavelengths are perceived as blue and purple colors, while longer wavelengths appear red. The wavelengths of visible light range from about 380 nanometers (violet) to about 740 nanometers (red). When all wavelengths of visible light are combined, they make white light.
When white light shines on an object, some wavelengths are absorbed while others are reflected. The reflected wavelengths determine the color we see. For example, a red apple absorbs most wavelengths of light but reflects wavelengths around 650 nm, which we perceive as red.
| Color | Wavelength range (nm) |
|---|---|
| Violet | 380-450 |
| Blue | 450-495 |
| Green | 495-570 |
| Yellow | 570-590 |
| Orange | 590-620 |
| Red | 620-750 |
This table shows the approximate wavelength ranges corresponding to different colors of visible light.
Color Perception
Although physics determines the makeup of light, how we actually experience color involves complex neurophysiology. Color perception arises from the way our visual system interprets light signals.
Light enters our eye and falls on the retina, where photoreceptor cells transduce the light into electrical signals. These signals travel via the optic nerve to the visual cortex in the brain. Here, intricate neural circuits analyze the signals to construct color.
Our retina contains two main types of photoreceptors: rods and cones. Rods are sensitive to brightness but do not provide color information. Cones are specialized for color vision. There are three types of cones that differ in their sensitivity to different wavelengths of light.
| Cone type | Peak sensitivity |
|---|---|
| S cones | Short wavelengths (blue) |
| M cones | Medium wavelengths (green) |
| L cones | Long wavelengths (red) |
This table shows the peak sensitivities of the three cone types which broadly correspond to blue, green, and red wavelengths.
The retinal signals from the cones are processed by neural circuits in the retina and brain. Parallel processing pathways analyze different aspects of the visual input, including color, motion, form, and depth. In the color pathway, neurons compare and contrast signals from the different cone types to extract color information.
Color Constancy
Remarkably, the colors we perceive remain relatively constant despite changes in illumination. This phenomenon is called color constancy. Consider looking at a red apple. Whether viewed under daylight, incandescent light, or shadow, we still perceive the apple as red.
Color constancy occurs because our visual system automatically adapts to changes in illumination. The brain analyzes the overall makeup of light and compensates so that object colors remain relatively stable. This provides a constant perception of color despite changing viewing conditions.
Various mechanisms contribute to color constancy, including neural adaptation to the illumination, internal normalization and ratios between cone signals, and influence from remembered colors of familiar objects. Higher cognitive processes can also influence color perception.
Color Deficiencies
For most people with normal color vision, color perception is remarkably similar. This is because our retinal photoreceptors and neural wiring closely follow a standard design. However, there are individual differences in how people perceive color.
Color deficiencies affect a significant portion of the population, primarily in men. The most common form is red-green color blindness where people have difficulty distinguishing between red and green hues. This arises from genetic mutations that alter cone photoreceptors in the retina. Other rarer deficiencies can affect blue-yellow perception.
Complete color blindness or monochromacy, where a person can only see shades of gray, is very rare. More often, color vision is simply anomalous and certain color distinctions are compromised. Although color deficient vision cannot be restored, adaptive tools and strategies can help compensate.
Color Subjectivity and Culture
Color perception also has subjective aspects. While the physics of light and the basics of color vision are universal, cognitive interpretation and color symbolism often have cultural influences.
For example, color preference and the color meanings we associate with objects are influenced by individual experiences and cultural factors. Red may signify danger in one culture and prosperity in another. Blue and pink can have strongly gendered associations.
Language also shapes color perception. Different cultures have divergent numbers of basic color terms that carve up the spectrum. Categorization by color terms can influence cognitive judgments of similarity between colors that fall within or outside language boundaries.
So in summary, although color has an objective basis in physics and vision science, subjective factors involving language, culture, and individual experience give color additional layers of meaning.
Conclusion
In physics, color originates from light of different wavelengths. But our perception of color involves complex neurophysiology and processing in the retina and brain. While physics determines the stimuli, the resulting color depends on how our visual system interprets those signals.
Color perception is an interplay between the physical makeup of light, the biological machinery of our eyes and brain, and the subjective influences of language, culture and experience. So in essence, color is constructed in our minds based on the physical world of light around us.