Humans can only see a small portion of the electromagnetic spectrum, which means we may not be seeing the true colors of the world around us. Our eyes have color receptors that allow us to see light in the visible spectrum, which includes all the colors of the rainbow. But many creatures can see wavelengths of light that are invisible to humans, revealing a colorful dimension we can scarcely imagine.
How human color vision works
The human eye has specialized cells in the retina called cones that allow us to see color. There are three main types of cones, each sensitive to different wavelengths of light:
- S cones – Sensitive to short blue wavelengths
- M cones – Sensitive to medium green wavelengths
- L cones – Sensitive to long red wavelengths
By combining input from these three cone types, the brain can perceive the entire spectrum of visible light, which ranges from about 380 nanometers (violet) to 740 nanometers (red). This range represents less than 0.0035% of the full electromagnetic spectrum, which extends far beyond what we can see.
Colors we can’t see
Many species can see parts of the electromagnetic spectrum that are invisible to humans. Bees, for example, see ultraviolet light, which allows them to spot the ultraviolet patterns on flowers that signal nectar within. Butterflies have an even broader spectrum, seeing from infrared through ultraviolet. Goldfish and birds see into the infrared range, detecting heat that enables them to find warm-blooded prey.
Some snakes can see infrared wavelengths, aiding their hunting of small mammals in total darkness. The pit viper specifically has heat-sensing pits between their eyes and nostrils that detect infrared radiation, generating a thermal image of their surroundings.
Mantis shrimp perceive an incredible range of color. They have 12 different types of photoreceptor cells (compared to our 3), extending their vision well into the ultraviolet range and also a bit into the infrared. They are essentially seeing an unimaginably broader spectrum of the rainbow.
True color imaging
Modern technology allows us to visualize some of the invisible parts of the spectrum. Night vision goggles detect infrared light to enhance visibility in the dark. Ultraviolet photography reveals hidden UV patterns in flowers and butterflies. But even these technologies only extend the range of human vision slightly.
To see the full splendor of the electromagnetic spectrum, a multispectral camera system is needed. This uses multiple filters to capture bandwidths extending from infrared to ultraviolet, then combines the images to produce a representative picture showing true color.
NASA frequently uses multispectral imaging for astronomy and satellite mapping. The images from space telescopes like Hubble and Spitzer reveal stunning cosmic phenomena in exotic wavelengths that far exceed human vision. Nebulas glow brightly in infrared, while interstellar dust shimmers in ultraviolet.
How other species see color
| Species | Color vision range |
|---|---|
| Humans | 380-740 nm (visible light) |
| Honeybees | 300-650 nm (ultraviolet to red) |
| Butterflies | 300-750 nm (ultraviolet to infrared) |
| Goldfish | 320-1000 nm (ultraviolet to near infrared) |
| Birds | 320-1000 nm (ultraviolet to near infrared) |
| Pit vipers | 400-1400 nm (visible to far infrared) |
| Mantis shrimp | 300-720 nm (ultraviolet to far red) |
This table compares the color vision ranges of humans to various other species. It illustrates just how limited human eyesight is relative to many animals. We only see about 1,000 nanometers of light, while mantis shrimp see over 400 nanometers more than us. Bees and butterflies also detect ultraviolet wavelengths that are invisible to us.
Tetrachromatic vision in some humans
A very small percentage of humans are estimated to have a fourth type of cone cell, giving them tetrachromatic vision. Their eyes contain four different color photoreceptors instead of three. Some scientists theorize this allows tetrachromats to perceive up to 100 million more shades of color than trichromats.
Having a fourth cone type with sensitivity to yellowish-green light enables tetrachromats to make more fine distinctions in hues along the red-green axis. Researchers suggest the common red-green colorblindness in males makes this fourth cone more prevalent in females, whose two X chromosomes increase the likelihood of producing a mutant color receptor.
But whether super-vision in tetrachromats actually exists remains controversial, as most tests have failed to prove they can discriminate colors outside the normal human range. More research is needed to firmly establish if tetrachromacy grants extraordinary color perception abilities.
Color perception influenced by language
Human color categorization is shaped not just by our eyes, but by our language. The words we have to identify colors affects how we group the spectrum into perceived boundaries. For example, some languages like Japanese have only one word that covers both green and blue.
Studies show that speakers of such languages are faster at discriminating between two shades within a category, but slower at discriminating between two shades spanning the boundary. This demonstrates how linguistic categories influence color discrimination.
Different languages also have varying numbers of color terms. Indigenous Australian languages have as few as two, contrasting light and dark. The Himba language of Namibia has five primary color words. English has 11 basic color terms, expanding the segmentation of the continuous visual spectrum.
So language and culture have a substantial impact on human color cognition. They shape our perceptual color categories and even influence how we interpret ambiguous colors along fuzzy boundaries.
How color vision evolved in humans
Humans evolved trichromatic color vision primarily to help find ripe fruit and leaves amid green foliage, according to leading theories. Detecting shades of red in vegetation would’ve enabled our primate ancestors to spot ripe food sources.
Color vision also helped female primates evaluate potential mates. spotting red tones in skin, fur, and genitalia that increase blood flow and signal fertility. So color sight emerged from survival needs to forage and reproduce.
Old world monkeys and apes have trichromatic vision like humans, but our divergence from other primates was marked by a gene duplication event. This produced multiple variants of the L and M opsin genes on the X chromosome, which code for the red and green cones. With three different photopigments, humans gained much finer color discrimination, likely for finding fruits amid leaves.
So human color perception appears specially adapted for seeing shades of red and green, at the cost of discriminating ultraviolet hues that many other mammals detect. Our eyes sacrifice a wider spectral range for superior discernment of useful colors within our narrow visible spectrum.
How altered perception reveals the limits of color
The quirks of human vision reveal that color has no intrinsic essence, but only exists within the observing mind. This subjectivity is highlighted by visual disorders that alter color perception.
In cerebral achromatopsia, a brain injury completely eliminates the ability to see color. Victims with this disorder describe a drab, gray world stripped of all color qualities. This reveals that color is not an objective feature of reality, but a quality constructed by the brain.
Meanwhile, people with synesthesia experience a blending of their senses, where they involuntarily see colors when hearing sounds or reading text. So the perception of color can get crossed with entirely unrelated senses in the brain.
These conditions demonstrate that color depends on complex cognitive processes in the observer’s visual system. It does not possess any self-contained qualities apart from the human brain conjuring color sensations from physical wavelengths of light.
Do colors exist beyond human perception?
Since humans only see a sliver of the electromagnetic spectrum, many scientists propose that colors exist beyond the limits of our vision. But others argue that color is an internal construct of the mind and not an external property.
The philosopher John Locke described this subjective view of color, known as color relationalism. He noted that the blind man operates as if color does not exist at all, so it can’t be intrinsic to the world. Color is not contained within light itself, but rather depends on an observer to generate the experience of color.
From this perspective, ultraviolet and infrared are not colors at all without a conscious agent to perceive them as such. There is no redness or blueness inherent to a wavelength. Color is created by the complex mechanisms and processing of a visual system.
So in a real sense, humans see the true colors – the only colors that exist. But many animals see additional colors adapted to their own visual systems, revealing a colorful world beyond our imagining.
Conclusion
The limited human perception of color serves as a profound reminder of the subjectivity of experience. Our eyes pick up but a sliver of reality. Color is not contained in objects themselves, but arises only in interaction with a visual system. Scientists still ponder if any intrinsic colors exist beyond those manufactured in our minds.
We can marvel at how many more vivid colors or ethereal hues may glow all around us, just beyond the veil of our senses. Technology can help part the veil, but not completely. The full scope of color remains constrained by the eyes we have to see.
