Is the existence of the color purple a matter of debate?
The world's spectrum of colors is a captivating spectacle; from lavender blooms to amethyst gems, purples are aplenty. But take a second glance at the visible-light electromagnetic spectrum, and you'll find that the distinct hue we call 'purple' is oddly absent.
Does that mean purple is nothing but an illusion? Not exactly. The dicey dynamics of brain color perception make this mystery intriguing and complex.
To be perfectly clear, purple does exist in the electromagnetic spectrum – typically spanning around 380 to 450 nanometers, residency being near the violet border [1][4]. Yet, the way our brain interprets light is what creates the vivid hue we call purple.
Zab Johnson, an executive director and senior fellow at the Wharton Neuroscience Initiative at the University of Pennsylvania, put it succinctly, "I'd say none of color actually exists. It's all the process of our neural machinery."
To better understand, remember that all colors trace back to light. As sunlight kisses our planet, varying wavelengths (infrared rays, radio waves, X-rays, ultraviolet rays, and more) pay their visit [2]. The visible light spectrum – the light our peepers can see – represents an insignificant 0.0035% of the total electromagnetic spectrum. This is the realm of the rainbow.
At one end, we find long wavelengths, the sort we perceive as red. At the other end, shorter, high-energy wavelengths, which we perceive as indigo and violet, reside.
In the back of our eyes, there are specialized receptors called cones. Humans have three types of cones, each sensitive to specific wavelengths: red, green, and blue. Light sparks these receptors, sending electrical signals to the brain. The brain, taking this data, forms a general consensus about what we're seeing [2].
Now, purple comes to play. When short-wave (blue) and long-wave (red) cones are stimulated, our brain concocts something that, in reality, isn't present on the earth. As Johnson pointed out, red and blue are opposite ends of the visible spectrum. When brain encounters these wavelengths, it curves this linear visible spectrum into a circle. Essentially, it brings red and blue together to create purple and magenta, even though light doesn't behave that way [3][4].
Consequently, purple and magenta are referred to as 'nonspectral' colors since they don't exist as actual electromagnetic radiation. Unlike these illusionary colors, spectral colors – from red, orange, yellow, green, to blue, indigo, and notably both violet and indigo – are made of just one wavelength.
For those curious about the cosmic spectrum of color, the sky appears blue thanks to a scattering effect known as Rayleigh scattering [5]. But that's a tale for another day.
Whether naturally produced or created by the grinding of sea snails, purple has held people spellbound for millennia. It even served as a signifier of power and wealth for the ancient Phoenicians, while being a hallmark of magic for us today [6]. Regardless of its tangible existence, purple remains unique and merits closer examination. After all, its intangible qualities are what make it truly special.
So, the next time you bask in the luscious shade of a lavender flower, gaze at the majestic dance of a purple emperor butterfly, or marvel at an iridescent amethyst, remember that you and our brains are the true creators of this whimsical, observable yet illusive display of purple.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5268361/[2] https://www.livescience.com/55841-how-humans-see-colors.html[3] https://www.livescience.com/20307-why-can-we-see-purple-but-not-yellow-green.html[4] https://www.livescience.com/53446-visible-light-visual-spectrum-explained.html[5] https://www.space.com/11653-sky-blue-question.html[6] https://www.sciencedaily.com/releases/2015/12/151208113854.htm
- Our brains play a significant role in creating the color purple, even though it doesn't actually exist in the electromagnetic spectrum as a distinct hue. This is because our brains combine the signals from red and blue cones in our eyes, which are opposite ends of the visible spectrum, to generate the perception of purple.
- Contrary to spectral colors that are made of just one wavelength, such as red, orange, and violet, purple and magenta are considered 'nonspectral' colors because they don't exist as actual electromagnetic radiation. Instead, they are an illusion created by the unique dynamics of brain color perception.
