Unlocking The Color Spectrum: A Deep Dive into the Science of Color Perception

A Deeper Look Into How Our Eyes Perceive Colors

by Tim Truth

The visible light spectrum encompasses wavelengths from approximately 380nm to 780nm, with each specific wavelength corresponding to a distinct color. These spectral colors, often depicted in series as the rainbow, are fundamental to understanding how we perceive color. Interestingly, by mixing these spectral colors, we can create entirely new colors like brown, pink, gray, magenta, and white (just to name a few).

Our modern displays, such as computer and phone screens, utilize the RGB (red, green, blue) color model to mimic these spectral colors. Each pixel on these screens combines varying intensities of red, green, and blue light to produce the wide range of colors we see. This method, known as additive color mixing, is essential in devices that emit light, including screens, lights, and projectors. We’ll discuss the biological basis for why these colors are chosen.

Here is the visible light spectrum. These are the spectral colors for each of the whole numbers in the visible light spectrum between 380nm and 780nm

All of these colors can be added (and subtracted) to create entirely different colors (brown, pink, gray, magenta & white for examples). Also, these single frequency colors of the rainbow can be created from mixing other colors. If your computer/ phone screen uses RGB, it just made each of the spectral colors by mixing red, green & blue light. We’ll discuss additive color (screens, lights, projectors) & subtractive color (ink, dyes, paints) later in this article.

Color Wheels

We’ve all seen the color wheels. Usually it is the rainbow series of colors bridged together with a magenta section gradient-bridging from red back to purple.

Note in the above rendition, Red, Green & Blue subdivide the wheel into thirds. The rainbow consists of colors known as the spectral colors, but there are many more colors possible via addition or subtraction of different colors.

In this color wheel, yellow plus these 3 primary colors (red, green & blue) evenly divide the wheel in fourths:

You’ll see these 4 colors in many logos like Google, Microsoft, eBay, older Windows logos, NBC, Google Chrome etc

All of the spectral colors can be mimicked by adding different amounts of red, green and blue together. This is actually what most of our computer monitors and phone displays do for each pixel. This next chart examines spectral colors with whole number wavelengths and then calculates how this is combined using just red, green & blue.

How We Sense Colors

The human eye perceives color through specialized photoreceptor cells called rods and cones, located in the retina. While rods are responsible for vision in low light conditions and do not contribute to color perception, cones are responsible for our ability to see colors. There are three types of cones, each sensitive to different wavelengths of light corresponding to red, green, and blue.

Red Cones (L Cones): These cones are sensitive to long wavelengths of light, roughly peaking at 564 nanometers. When red light enters the eye, it stimulates these cones more than the green or blue cones. The brain interprets the level of stimulation from the red cones, along with input from the other cones, to perceive the color red.

Green Cones (M Cones): Green cones respond best to medium wavelengths, with a peak sensitivity around 534 nanometers. When light in this wavelength range hits the retina, the green cones are most activated. The brain uses the information from these cones, in conjunction with the red and blue cones, to construct our perception of the color green.

Blue Cones (S Cones): Blue cones are sensitive to short wavelengths, peaking at approximately 420 nanometers. These cones are less numerous compared to the red and green cones, yet they play a crucial role in detecting blue light. The combined response of blue cones, along with red and green cones, helps the brain determine shades of blue and other colors.

Seeing certain colors leaves a lot of unknowns about their actual photon frequency composition. Take, for example, yellow. When we perceive yellow, it could be composed of any of these three combinations:

1. Pure yellow light: Photons with a wavelength near 575 nm.

2. Red and green light added together: A combination of red light (photons with wavelengths around 650 nm) and green light (photons with wavelengths around 530 nm).

3. Red, green, and yellow light added together: A mixture of photons with wavelengths corresponding to red, green, and yellow.

Our eyes have three types of photon-sensing cones, each tuned to different frequency ranges, which makes this possible. When it comes to the above three examples of yellow light compositions, consider how the two relevant cones perceive these:

• Pure yellow light (575 nm): The yellow light stimulates both the red and green cones to some extent, because the response curves of these cones overlap in this region.

• Red and green light added together: The red cones are stimulated by the red light, and the green cones are stimulated by the green light. When both types of cones are activated simultaneously, our brain interprets this combination as yellow, even though there is no actual yellow wavelength present.

• Red, green, and yellow light added together: In this scenario, the red and green cones are stimulated by their respective wavelengths, and the additional yellow light adds to the overall stimulation. This can create a more intense perception of yellow or a slightly different hue depending on the exact intensities and ratios of the lights involved.

This phenomenon is a result of the way our photoreceptors respond to light. Here’s how the cones work for each scenario:

1. Pure yellow light: Red cones and green cones both respond, with the green cones typically having a stronger response because their sensitivity peak is closer to 575 nm.

2. Red and green light added together: Red cones and green cones both respond, but here they each respond to their respective wavelengths. The brain averages these responses, leading to the perception of yellow.

3. Red, green, and yellow light added together: Red cones and green cones respond to the red and green components, respectively, and both respond to the yellow component. The combined response from all three types of light can enhance the perceived intensity of yellow.

Understanding these interactions can help in various applications, such as color display technology, lighting design, and even in creating visual art, where manipulating light and color can achieve desired visual effects.

So considering the photon sensors within our eyes is a must to understanding the relationships between colors and reasoning about why they affect us different.

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