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Facts of the Matter Richard Brill |
Color is the
primary carrier
of informationColor is so ubiquitous that most of us take it for granted. Yet, our ability to discriminate millions of colors and distinguish between them is the basis for such diverse things as fireworks, the study of stars, the production of dyes, and the detection of pollution, to name a few.
Color is not a thing, but rather a perception based upon the interaction of light with specialized cells called cones, of which there are six million or so concentrated in the macular region in the center the retina at the back of the eye.
Another type of light sensitive cells numbering around 120 million, called rods, are sensitive to shades of gray and allow us to see in dim light.
Three types of pigments in cones absorb blue, green and red light, the triad of primary colors that in various combinations create the spectrum of color on the artist's pallet.
White light consists of the three primaries in equal proportion and is sometimes said to contain all of the colors.
Light of any color can be separated into its constituents by a prism, or by a spectroscope, which allows us to measure the relative intensity of the light of different colors as well.
We never see pure colors, except for the light produced by a laser. We see combinations of colors, similar to the way we hear music colored by overtones and harmonies of different instruments and voices to produce different timbres.
Color doesn't come from the things we see, it comes from the interaction of light and substance, with each substance contributing its own unique signature of color through the interaction.
Color is an atomic phenomenon, at its most fundamental the interaction of light with electrons, specifically electrons that are confined within the atom as they transition between orbits.
Every transition entails a gain or loss of energy by absorbing or emitting a quantum of light energy called a photon. It is the energy of photons absorbed by the cones that we perceive as color: More energetic photons are associated with larger level changes and bluer light; the redder the light, the less energy carried by each photon.
Energy transitions by electrons are roughly analogous to moving up and down between floors of a skyscraper, except that in the atom the spacing between the lower levels is greater and becomes progressively smaller with distance from the center of the atom.
Imagine all of the possible changes in level from every single floor of such a building to each and every other floor and you will begin to see the complexity born from simplicity that produces the variety of colors in our environment. Then to fully appreciate it, multiply that by a nearly infinite number of "buildings," representing the number of different possible combinations of different kinds of atoms!
Energy transitions within atoms are responsible for the richness of color in our environment. But not all atoms, or combinations of atoms, are equally adept at producing colors. Each substance has a unique chemical composition. As a result, its atoms have a unique pattern of electron energy level changes, which produce a unique combination of colors.
Only a fraction of the transitions produce visible light. Many involve photons in the infrared or ultraviolet range while many others involve a multitude of transitions with energies that span the spectrum and so produce grays or washed-out colors.
When light interacts with an object, either by reflecting off the surface or by passing through it, a stream of photons bombards the electrons in the atoms of the substances that comprise it. All of the light impinging on any substance is either reflected from, transmitted through or absorbed.
Most of the colors around us, both natural and man-made, are due to reflection of certain colors that were not selectively absorbed.
The moon and the planets shine by selectively reflected light as well. This coloration is the effect of the properties of electrons in atoms of a select group of metals -- such as iron, chromium, manganese and copper -- chemically combined with with atoms of a very few oxidizing substances -- such as oxygen, sulfur, or halogens such as chlorine and fluorine.
Pigments used in paints are likewise given their colors by the presence of metals.
Most of the other colors on Earth are due to selective absorption and reflection by organic molecules, themselves created by energy from sunlight via photosynthesis. The green color of most plants, for example, is due to the use of red and blue photons but not green.
A small, but significant source of color are self-luminous objects in which the light comes when electrons that have been energized by heat or electricity fall back to lower levels and release quanta of energy as photons.
All forms of artificial light, incandescent, fluorescent and luminous plasma as well as stars, including our own sun, emit light as electrons energized by heat or electricity spit out photons when they retreat back to the lower energy levels within atoms.
Neon lights, fireworks and astronomy all rely on the unique signature of color that emanates from them, the sensitivity of the retinal cones, and the brain that puts it all together.
All light, regardless of its source, carries information about the substances from which it emanated and with which it has interacted. It is the primary and most fundamental carrier of information that we receive from our surroundings, and our scientific instruments are merely precise extensions of the same sensory abilities that allow us to distinguish a ruby from a sapphire.
Using those instruments to analyze the colors and the intensities of light, we learn about distant galaxies, stars and planets and extend the boundaries of our physical laws. We use them to analyze the composition of substances here on Earth, to detect and measure the amounts of trace chemicals in food, water and tissue. We use our knowledge to produce the brilliant colors of "neon" lights, create synthetic dyes for clothing, cosmetics and food and to combine different metals with other substances to produce new colors and extraordinary brilliance in pyrotechnics.
If the colors of the fireworks at this year's July 4th celebration seemed brighter, it wasn't just our imagination fueled by the childish, yet deeply human fascination with fire. It was because the better we understand the nature of color and the nature of the atoms that produce it the better we are able to combine just the right metals in just the right combinations with just the right oxidants to produce those colorful and noisy explosions for no other reason than to enjoy the show.
Richard Brill picks up where your high school science teacher left off. He is a professor of science at Honolulu Community College, where he teaches earth and physical science and investigates life and the universe. He can be contacted by e-mail at rickb@hcc.hawaii.edu