Vision
Shades of green make the world spin
1. Greenery
Green used to be a color associated with the natural world. Nowadays, that association is past bygone.
Currently, the natural wavelengths that vary from 495 to 570 nanometers in the light spectrum, caught up between yellow and blue, display another universal meaning with their green hue:
Wealthy funds.
And if you think money grows on trees, you can bet you are right!
But it comes in the form of Nature’s bitcoins: chlorophyll.
It is the natural currency that allows the market exchanges that enable plants to absorb the energy they need from sunlight to build tissues.
2. Chlorophyll
Chlorophyll is a pigment molecule found in the membranes of chloroplasts, in photosystems that enable any plant’s metabolism. They absorb light in the biochemical trade market.
Complex interactions between light and sophisticated microstructures such as chlorophyll and our retinal cells allow us to perceive shades of green.
When a tree leaf is illuminated with white light, we perceive the particular wavelength range that is reflected by the pigment chlorophyll whilst the other wavelengths are absorbed by that same leaf. That means chlorophylls absorb mostly the blue and red portions of light and reflect the green and near-green portions of the light spectrum.
Whenever the pigment’s electrons absorb energy, they change layers and release photons in response to the light stimuli.
Then our retinal cells interact with the emitted energy and depending on its wavelength, we perceive different color tones.
If our eyes are apt.
Some say the grass is always greener on the other side. One cannot make such assumptions because our eyes are not able to make those subtle distinctions.
But birds of prey could.
Their UV-sensitive visual system allows them improved sight for green vegetation, thus facilitating their flight through such cluttered environments.
We would have to do proper research with a spectrometer. Either way, that metaphor can only be applied by those who can actually distinguish all sorts of color tones.
Many people cannot. People who are color-blind or have some form of color vision deficiency cannot perceive all colors in the spectrum of visible light (380 to 780 nm).
Lines between red and green can be blurred for them.
This condition is called color-blindness but can also be known as daltonism or protanopia.
It must be hard to live in a noninclusive world with any kind of deficiency. There are those, however, trying to pave the way to a more inclusive and accessible science.
3. Structural colors
Structural colors are those with a purely physical origin found in Nature. They differ considerably from the ordinary coloration mechanisms found in pigments, like hair color.
When we take a peek at a peacock’s tail, we observe different phenomena than merely staring at a green leaf.
Here, the interactions are far more sophisticated to create this holographic effect, and they do not depend solely on pigmentation. Our perception of the so-called structural colors occurs due to light in accordance with the angle of incidence of the light rays.
Energy itself is not lost in such interactions. What we see is the result of various types of spatial inhomogeneity that act as obstacles to light scattering. The same thing happens when we observe a sunset. The colors in the sky change because the angle of incidence changes, in accordance with Snell’s Law.
Since light behaves as waves (meaning that it travels in one direction and oscillates back and forth in a direction that is perpendicular to the original direction), whenever it hits a medium that reflects or filters part of the incident light waves (acting like optical lenses), light undergoes reflection, polarization, scattering, and deflection asides absorption.
That explains why the color changes with different viewing angles, a phenomenon also called iridescence. Many animals have structures that produce structural colors, the more widespread are undoubtedly insects.
But these phenomena can also occur naturally in surfaces by thin-film interference like in soap bubbles and oil leakages, as well as some minerals depending on their tridimensional array.
4. (Bullet with) Butterfly wings
Most of the structural colorations are originated from multilayer interference with anatomical structures.
For instance, a butterfly wing changes its color as we change our viewing angle. The degree of color change is dependent on each species.
I don’t know about the bullet, though.
Butterflies and moths are insects that belong to the Lepidoptera order, amidst other estimated 150 thousand species.
Of those, only three superfamilies are devoted to butterflies (Papilionoidea, Hesperioidea, and Hedyloidea).
And I must say they have very curious names. Trapezitinae, Dismorphiinae, Nymphalinae, Morphinae, Satyrinae… Just to name a few.
All Lepidopteran species have their wings covered with different types of scales. These are thin plate-like forms that cover their wings like tiles on a roof or a dense tapestry, as shown in close up in the illustration:
Usually, two types of scales are present in butterflies: ground (basal) scales and cover scales over them, acting as a specialized glass cover. The latter are variously in shape and play a variety of roles on the wing, whereas the ground scales usually are rectangular and less specialized.
The upper scales create an effect similar to a thin layer interference (like soap bubbles) and the wings change their color in accordance with the refraction angle of the medium they are immersed into:
5. Greed
Unfortunately, Science has not explained this human feature well enough.
Perhaps we should ask those that kill birds for green profit or greedy self-indulgence.
