The Truth About Color Vision

May 14, 2019 Kayode Oseh

Color vision is the ability to identify objects using frequencies or light wavelengths. We perceive light based upon its absorption or reflection from an object. In basic terms, color is light. Color doesn’t actually exist in the absence of light, but is perceived by the brain in humans, insects, and other animals. Color vision, is therefore, very subjective. One person’s perception of color may be completely different from another.

Rods and Cones

Cones, found in the retina, are photo-receptor cells that work best in bright light. They are responsible for eye color sensitivity and color vision. Cones, along with Rods, help us define and differentiate what we see. However, Rods are specifically for dim light and are only capable of black and white. Cones and Rods got their name from their distinctive shapes. Cones and rods receive the light and translate the light as messages or signals that are then sent to the brain.

Red, Green, and Blue

There are three different types of cones in the human eye. The three types of cones in the human eye are: Red (long), Green (medium), and Blue (short). Red, green, and blue are considered “primary colors.” The human eye can see nearly every gradient of colors when red, blue, and/or green are combined together.

How Does Color Vision Work?

Light comes through the eye through the cornea of the eye. The pupil of the eye controls the amount of light that comes in to the eye, by adjusting the size of the pupil. In brighter light, the pupil doesn’t require as much light and adjusts by getting smaller, so less light comes in. In low-light situations, the pupil dilates, or gets bigger to let more light in. The cornea is the thin, clear membrane that covers the front of the eye and protects our eyes from foreign objects. The cornea bends or refracts the light as it passes through the eye. The lens sits right behind the pupil of the eye. The lens of the eye focuses the light coming in, onto the retina.

The rods and cones are located on the retina and act as “photo-receptor cells” that convert the light into electrical messages that are then sent to the brain through the optic nerve, for the brain to process and make sense of the information sent from our eyes. We see color if the light is bright enough for the cones to process the light signals. In low light, we see in black and white, when the rods work best process the light information.

500 Shades of Grey

The human eye can distinguish between 500 shades of grey. A normal human eye can detect over 7 million colors! Most of the colors we see are the combination of more than one color or some sort of blend of red, green, and/or blue. Objects absorb and reflect light and color differently. It is the colors that are reflected from an object that we actually see. For example, a black object absorbs all colors and reflects none, therefore, the object appears black to the observer. The blue sky absorbs all colors, reflecting blue. Therefore, it is the blue color we see. A green leaf absorbs all the colors, except for green. The leaf reflects green and it is the color we actually see.  An apple is red, because it reflects red light.

Color Blindness

Color Blindness occurs in about 2% of the human population. Color blindness is not really blindness at all. It is the inability to distinguish colors. The most common occurrence of Color Blindness is defined by the inability to differentiate between red and green. Most mammals with color blindness see colors in differing shades of blues, greys, and yellows. Women are far less likely to be color blind than men. 1 in every 200 women are affected by color blindness, while it affects 1 in 12 men. The cause of color blindness is missing or damaged cones in the eye. Most commonly, in humans, the missing or damaged cones are the red and/or green cones.

It’s Black and White

Black is actually not a color. It is the absence of color. White isn’t actually a color, either. It is actually the blending of all colors of the spectrum. The combination of all colors of light, result in white light. White light, such as sunlight, appears colorless or white. Like a rainbow, white light is composed of all the colors of the light spectrum.

White Light and Prisms

White light is made up of all the visible colors. This can be observed using a triangular prism, and colors can seen separately, as this light splits, according to each color’s wavelength, through the prism. As a narrow beam of light is reflected on one plane of the triangle, a spectrum of colors can be seen on the other side. This occurs because the light passing through the triangular prism is refracted or bent by the angles and flat sides of the prism. Each color represented in the white light is refracted differently and each wavelength or color, bends at a different angle. This results in an arc of different colors that spread out into a beautiful rainbow.

The Long and Short of It

Wavelengths vary widely. Ultraviolet light, for example, has a shorter wavelength than visible light, and therefore, humans cannot see ultraviolet light with the human eye. Visible light is the light that corresponds with a light wavelength of 400-700 nanometers. Violet has the shortest wavelength and red has the longest wavelength of visible light. Infrared light has a longer wavelength than visible, red light. Infrared light falls outside the scope of what is considered visible light for humans, although some other animals can perceive light outside of this range.

Rainbows

When tiny water droplets are in the air, they can act as miniature prisms. Much like what happens when light passes through the triangular glass or plastic, when light passes through a water droplet, a spectrum of light can be created in the sky.  As light enters a raindrop, it slows down, because light is slower in water than in air. The light bounces off the back of the raindrop and exits the raindrop, however, the light speeds up and is once again, refracted as it exits the droplet.  Rainbows are created when light enters a water droplet and the light is refracted or bent, then reflects on the side and is refracted again, as the light exits.

What do animals see?

Can other animals see colors? Do they see more or less color than humans? While we can’t say for sure, scientists can count the numbers of cones in an animal’s eye and the position of the cones, in relation to the retina, to make educated guesses about the number of colors and how strongly the color might be seen. Spiders, bees, and many other insects can see an additional color that humans cannot see—ultraviolet. Reptiles and snakes can see infrared, in addition to some color.

500
Leave a comment...