The visible color spectrum is the range of colors that the human eye can perceive. It runs from violet and blue on one end, through greens and yellows, to orange and red on the other end. One notable omission from the visible spectrum is the color brown. This article will examine why brown is not considered part of the main visible color spectrum.
The visible spectrum is composed of wavelengths of light that range from about 380 to 740 nanometers. Violet light has the shortest wavelength, while red has the longest wavelength. When all the wavelengths are combined, they make white light. The various colors we see result from only some wavelengths reaching our eye.
For example, an object that absorbs all wavelengths except those around 420nm will appear violet to our eyes. An object that absorbs all but the longest wavelengths near 700nm will look deep red. Our eyes contain special receptors called cone cells that detect these wavelengths and allow us to see color.
The Nature of Brown
So where does brown fall in this spectrum? Brown is interesting because it does not correspond to a specific wavelength of light. Brown is formed when an object absorbs more blue light and reflects more red and green wavelengths. This makes the light coming from the object appear brown to our eyes.
Essentially, brown is a mix of various wavelengths, not a pure color with a singular wavelength like the other colors in the spectrum. It is created through a subtractive process of absorbing some colors more than others, rather than emitting a particular wavelength.
Additive vs. Subtractive Color Mixing
To understand this better, it helps to contrast additive and subtractive color mixing.
The visible spectrum uses additive color mixing. This refers to mixing various wavelengths of light together to create other colors. For example, red light around 700nm combined with green light around 520nm will appear yellow to our eyes. All the wavelengths together make white light.
In contrast, subtractive color mixing involves selective absorption of some wavelengths. For example, a brown object may absorb more blue and violet light, leaving mostly yellow, orange and red wavelengths to be reflected. This gives the brown appearance. Other colors like cyan and magenta work similarly.
Additive mixing produces pure spectral colors with specific wavelengths. Subtractive mixing produces non-spectral colors without a dominant wavelength. Brown arises through the latter process.
| Additive Color Mixing | Subtractive Color Mixing |
|---|---|
| Mixing light colors | Absorbing some light wavelengths |
| Produces pure spectral colors | Produces non-spectral colors |
| Example: Red + Green = Yellow | Example: Absorbing blue -> Brown |
Brown’s Place on the Color Wheel
The visible color spectrum is often depicted as a color wheel, showing the transition from violet to red through the other spectral colors. Brown does not have its own place on this wheel. However, it exists between red and yellow, blending those hues together.
On an artist’s color wheel showing mixtures of paint pigments, brown occupies the transitions between primary colors. For example, between red and green sits the color termed “raw umber”. Between yellow and purple lies “raw sienna”. These browns again show the subtractive mixing of pigments.
So while brown does not have a dedicated spot between violet and red, its position on color wheels represents the blending between surrounding spectral colors.
Brown in Nature
While not a spectral color, brown is extremely common in nature. Soils, bark, autumn leaves, fur, and feathers are just some examples of items that display rich browns. The browns arise from selective absorption of some wavelengths over others.
For instance, soils contain iron oxides that absorb bluer wavelengths, leaving warmer reds and oranges to predominate. Leaves turn brown in autumn as their chlorophyll breaks down and other pigments come to the fore. These organic pigments favor passing along yellow and red wavelengths while absorbing some greens and blues.
By preferentially absorbing or scattering certain wavelengths, a wide array of living and non-living items display the color brown, from rocks and sand to mushrooms and deer.
Useful Color Perception
The fact that our eyes perceive browns as distinct hues, despite their non-spectral nature, is an adaptation to be sensitive to the natural environment. It is useful to see soils, leaves, trunks and animals as brown rather than just mixing reds, greens and blues. This categorical perception into distinctive color groups aids identification and scene understanding.
So while brown does not exist as a monochromatic wavelength, our visual system is attuned to categorize ranges of subtracted wavelengths as “brown”. This allows us to efficiently interpret the natural world. Our color vision nurtures useful perceptual constructs like brown.
Conclusion
In summary, brown is not considered a color within the visible light spectrum because it does not correspond to a single wavelength. The spectral colors arise from specific wavelengths of emitted light.
Brown instead results from subtractive color mixing, absorbing some wavelengths more than others. This causes a mix of remaining colors that we perceive as brown. While brown lacks its own pure hue, it occupies the transitions between other major colors on the artistic color wheel.
Our visual system adapted the useful construct of brown to represent the range of subtracted wavelengths common in nature. So while not spectral, brown provides valuable perceptual categorization. The absence of brown from the visible spectrum arises from physics, but its perception is grounded in biology.
