Green is a color that is ubiquitous in nature. From lush green forests to rolling green hills, the color green dominates many natural landscapes. But where does this vibrant color come from? Can green exist without blue?
The Science of Green
In order to understand green, we first need to understand a bit about how color and light work. The visible color spectrum that humans can see consists of a range of wavelengths of light. This spans from red light with longer wavelengths to violet light with shorter wavelengths. Somewhere in the middle of this spectrum is green light.
When light interacts with objects, some wavelengths are absorbed while others are reflected. The wavelengths that are reflected determine what color our eyes perceive. Green objects reflect more green light waves while absorbing other colors. Plants appear green because the chlorophyll pigment in their leaves absorbs blue and red light while reflecting green.
But there is more to the perception of color than just reflecting a single wavelength. Most colors we see are a combination of multiple wavelengths. This is where blue comes into the picture for green. While green objects may primarily reflect green light, they also reflect a bit of blue. It is this combination of mostly green with some blue wavelengths that creates what our brain recognizes as the color green.
Primary Colors of Light
The primary colors of light are red, green, and blue. This is different from the primary colors of pigment which are cyan, magenta, and yellow. With light, the primary colors can be combined to create all other colors in the visible spectrum through a process called additive mixing. This can be demonstrated with red, green, and blue stage lighting:
| Red + Green | Yellow |
| Red + Blue | Magenta |
| Green + Blue | Cyan |
| Red + Green + Blue | White |
As you can see from this table, combining green and blue light makes cyan. This demonstrates that green requires blue as a primary color of light in order to exist.
Color Perception in the Eye
Taking a closer look at the anatomy of the human eye reveals more about the relationship between green and blue. There are two types of photoreceptor cells in the retina of the eye that detect color – cones and rods.
The cones are specialized cells with pigments that are sensitive to different wavelengths of light. There are three types of cones:
- S cones – sensitive to short blue wavelengths
- M cones – sensitive to medium green wavelengths
- L cones – sensitive to long red wavelengths
The output from these three cone types is processed by the visual cortex of the brain to produce all the colors we see. The M cones in particular detect green light. However, they also pick up some input from the S cones that are sensitive to blue light. This blue response contributes to our neural perception of green.
Pigment Mixing
With pigments, such as paints and dyes, colors work differently than light. Pigments selectively absorb certain wavelengths while reflecting the others. The reflected wavelengths are what we see as the color. The primary colors of pigment mixing are cyan, magenta and yellow.
These primary pigment colors combine to create secondary colors. Green is a secondary color formed from cyan and yellow pigments. Cyan absorbs red while reflecting green and blue. Yellow absorbs blue while reflecting red and green. When combined, the reflected blue of cyan and reflected green of yellow mix to create the green we perceive:
| Cyan Pigment | Reflects Green and Blue |
| Yellow Pigment | Reflects Red and Green |
| Cyan + Yellow | Reflects Green → Green Color |
So with pigment mixing, green can be created by combining cyan and yellow only. But the perception of green still originates from the combination of green and blue wavelengths.
Computer Displays
On digital displays like computer monitors and phone screens, colors are created using light-emitting pixels. Most modern devices use LCD or OLED screens where each pixel contains a red, green, and blue subpixel. Varying the intensity of these subpixels allows the generation of all colors through additive light mixing, similar to stage lighting.
This means that on digital displays, green pixels rely on having both a green and blue subpixel within each pixel. The intensities of these two components can be adjusted to precisely control the hue of green that is output. So again, blue light is intrinsically necessary to create the greens we see on most screens.
Natural Green Without Blue
From the above examples, it is clear that blue light or pigment is essential for generating most greens that we encounter. But there are some rare exceptions to this in nature.
One example is the green sulfur bacteria Chlorobium. These bacteria contain a special chlorophyll pigment called chlorobactene that absorbs reddish-orange and near-infrared light while reflecting green.
So Chlorobium is able to reflect vibrant greens without utilizing blue light. However, this is highly unusual. Most natural greens leverage a combination of blue and green to achieve the green color we recognize.
Impossible Greens
Humans can only see light in the relatively narrow visible spectrum. However, we can imagine hypothetical greens that exist outside this range. Greens that only reflect light in the infrared or ultraviolet spectrum would be impossible for our eyes to see. An alien species might be able to perceive such greens.
There could also be imaginary greens that reflect completely unnatural wavelengths of light. In these hypothetical scenarios, green might not need blue at all since the rules of physics wouldn’t apply. But real greens that humans can observe seem to universally require some amount of blue.
Conclusion
In summary, the color green predominantly arises from medium wavelength light around 510 nanometers. However, the perception of green also requires some stimulation of the receptors in our eyes that are sensitive to blue wavelengths around 450 nanometers. Therefore, the color green as we know it cannot exist without also evoking a blue response.
This is consistent across the principles of light, pigments, and digital screens. The only exceptions are a handful of exotic biological pigments that can reflect green by absorbing non-blue wavelengths. Otherwise, blue seems to be an indispensable component of green in our visual world.
So when you admire the verdant greens of a lush forest or leafy plant, know that you are actually seeing a fusion of green and blue light, partnered together to produce the lovely colors of nature.
