HAVE you attempted to make your way around a pitch-dark room? Or have you ever closed your eyes tightly and tried to go about your daily activities? You may have found it rather frightening. It is a real relief to see the light! The inspired words of the Bible are indeed true, “The light is also sweet, and it is good for the eyes to see the sun.”—Eccl. 11:7.
The sun is our main source of illumination. Every second of every day it is changing four million tons of its matter into energy. This is sprayed out in all directions from its surface at over 186,000 miles a second! But what is the nature of these emissions? How do they make vision possible? And how is it that they enable us to see such a great variety of colors?
What the Sun Gives Out
The emissions from the sun are called “electromagnetic energy” or “radiation.” This radiation is frequently viewed as a stream of tiny particles. But, at the same time, it is also viewed as traveling in waves. Commenting on this apparently contradictory view, Professor Walter J. Moore said: “This unwillingness of light to fit neatly into a single picture frame has been one of the most perplexing problems of natural philosophy.”
While all radiation, including light, travels from the sun at the same speed, it is not all the same. There are many kinds. Some kinds of radiation have very long wavelengths, being measured in miles. Others have very short wavelengths, measured in tiny fractions of millionths even thousand-millionths of an inch.
Radiations that have longer wavelengths include heat waves and the very long radio waves. And among the shorter radiations coming from the sun are ultraviolet rays, X rays, gamma rays and the very short cosmic rays. But none of these are visible to human eyes, and so they are sometimes called invisible light. However, in between the longer heat waves and shorter ultraviolet waves is a very narrow band of wavelengths that are visible. So the part that we see is only a very narrow band in the middle of a broad spectrum of wavelengths, from cosmic rays to radio waves and electrical currents.
Radiations Reaching Earth
Not all radiation the sun sends toward earth reaches here. This is because earth’s atmosphere acts as a shield. Thus what reaches earth are essentially the wavelengths of visible light, with a restricted range of invisible waves. How glad we can be that our atmosphere keeps out most invisible radiation, for if it were permitted to reach earth it would kill us all!
On the other hand, we can be grateful that visible light floods our earth in such abundance. Plants capture the energy from light and employ it in converting carbon dioxide and water into a simple sugar that is the basis of all food. Without this energy from light, plants could not grow, and nothing could live on earth.
Wavelengths That Give Color
But light gives us much more. It blesses us with gorgeous color and beauty. What is so remarkable is that the band of visible wavelengths that give us light and the many colors is so narrow. These wavelengths measure from only about thirty-two millionths of an inch from crest to crest, which our eyes recognize as red, to about sixteen millionths of an inch, which we see as violet!
Traveling at the speed of light, as these rays are, the number of waves striking the eye are between about 375 and 750 million million a second. This vibration the human visual system interprets as light, the color corresponding to the frequency of the vibrations.
Light’s Numerous Colors
Does it seem strange to you that we should speak of light as being composed of different colors? Did you think that it was all white? Well, it usually appears white to our eyes because all the wavelengths of visible radiation are traveling together. They are unseparated. But when the wavelengths are separated, we can see their individual colors.
You might check this for yourself sometime. You can hold a long-playing phonograph record up to the light and look along its finely ridged surface. The light will be diffracted and you can see the light’s various colors. Or you may have observed after a rainstorm how the tiny droplets of water in the air have separated sunlight into its basic colors—violet, blue, green, yellow, orange and red—producing a beautiful rainbow.
This does not mean that light can be separated into only these few colors. It can actually be split into tens of thousands of different wavelengths, each producing a different hue or shade of the basic colors! The eye, however, cannot distinguish between the color of one wave of light and the color of another wave if they are too similar in length.
Studies have revealed that the human eye can distinguish about 128 separate shades of color in visible light. But in order to distinguish even this many, one wavelength of light must be projected on a screen, and before it is removed, another one of a slightly different wavelength must be projected alongside. Only by visually comparing them can the eye tell the difference between more than a hundred colors in visible light.
The Source of All Color
For a moment raise your eyes from the printed page, and look closely at certain things around you—perhaps a bookcase, a desk or even the floor. Is it not amazing what a great variety of color there is? But from where does all the color come?
Color does not exist in the desk, the floor or whatever object at which you may have been looking. True, we may speak of these things as being of a certain color. But the truth is, we do not live in a world of colored objects. The color of things is actually in the light that shines upon them. Light is the only source of color, and without light not even the faintest color exists.
But how is it that we can see light with its innumerable wavelengths of color?
Light cannot be seen as it travels through space, any more than can radio waves and other radiation. What causes light to become visible to the eye are the material substances upon which it falls.
For example, if we were in a room without particles of dust or even air, we could not see the beam or path of light from a flashlight if one were turned on. A beam of light in a vacuum is quite invisible. Thus when the astronauts in space looked out their window they could see the brilliant sun, but the sky was black. Black is the absence of light or color. The sun did not light up the sky because space does not have substances upon which the sun’s light can fall. We can see light only when it hits some object that will reflect its waves to our eyes.
Well, then, what causes an object to appear a certain color? Why are most plants and trees green and the sky usually blue? And why does the sky sometimes turn deep orange or red near the horizon in the evening?
Producing Color in the Sky
Our sky is filled with air, as well as tiny particles of vapor and dust. Earlier we noted that the atmosphere shields us from deadly radiation. It acts like a giant mirror to reflect most of such radiation back into space. However, light penetrates this shield, but in so doing many of its waves are scattered by the particles of air. The size of these particles is such that the shorter blue waves are scattered far more than others. Thus the sky has a blue color.
But when the sun is near the horizon it can be different. The more horizontal angle of sunlight shining through a dust-laden atmosphere tends to scatter light’s longer waves, causing the sky to take on a deep orange and red appearance. Thus, back in 1883, after the Krakatoa volcano erupted violently and scattered dust particles through earth’s atmosphere, the world enjoyed a series of remarkably beautiful sunrises and sunsets.
How Most Color Is Produced
However, the scattering of certain wavelengths of light is not the principal way color is produced. Most objects receive their color as a result of their absorption of certain wavelengths of light and their reflection of the others.
For example, most plants and trees are green, due to the particular arrangement of the pigment molecules in the chlorophyll. When sunlight falls upon the chlorophyll, most of the shorter violet and blue waves of light are absorbed, and so are most of the longer red waves. These wavelengths of light are used by plants and trees in the manufacture of food. However, primarily the green waves of light are reflected, and that is why we see plants and trees as being green.
The colors of man-made things, such as paints, dyes and inks, are produced in the same way. Their pigment molecules absorb certain wavelengths—or we might say that they subtract a certain part of the narrow band of light. Then they reflect back the part that is not absorbed, or subtracted. Thus, it is the combination of the reflected wavelengths—that is, the mixture of all the colors of light that are not absorbed—that give color to most objects that we see.
So a red dress is red because the dye absorbs, or subtracts, the other wavelengths and reflects red light. Asphalt is black because the molecules of its pigment absorb all wavelengths, and reflect very little of any of them. On the other hand, we see an object as white when it reflects equally all colors of light, which together comprise white.
Pigments actually reflect at least some wavelengths of all colors. Theoretically, if two colors each reflected only one wavelength, then when they were mixed black would result. But as it is, we can mix blue and yellow paint and get green paint. This is because blue paint also reflects green light, and yellow paint also reflects green light. So when they are mixed, blue light is absorbed by the yellow pigment, and yellow light is absorbed by the blue pigment. This leaves green light, common to both, to be reflected, producing green paint!
The variety in combinations of light as it is reflected from things around us staggers the imagination. Since no wavelength is fully absorbed, we see the world around us in a wonderful array of colors. It has been estimated that about ten million colors exist!
A factor in the color of an object, in addition to how it absorbs and reflects light, is the nature of the light itself. The energy of sunlight is distributed evenly through all the colors, but this is not so of artificial light. The fluorescent lamps often used in stores are strong in blue light. However, incandescent light bulbs lack in blue wavelengths, and so emit a yellowish light. This can affect your shopping.
For example, you may buy a red dress in a store that has fluorescent lamps. But when you get outside in the sunlight you may be surprised to see how much more red the dress really is. This is because the fluorescent lamps, with a concentration of blue light, did not produce a sufficient amount of red wavelengths to be reflected by the dress. Or, in a store lighted by incandescent bulbs, you may think you are buying a black suit. But when you get outside in the sunlight you find it is blue! In the store the incandescent light provided no blue wavelengths to reflect, and since the suit absorbed all other wavelengths it looked black.
Colors by Another Method
There is yet another important method by which colors are produced, and that is by the surface structure of some objects. Many of the most beautiful colors displayed by living things result from the way their bodies separate light into its constituent waves.
Consider, for instance, a butterfly that appears a metallic blue color when looked at from above, but appears crimson when looked at along the surface of the wing. The different colors are produced by the way the light is diffracted by the finely grooved surface of its wing. This can be demonstrated. Soft wax can be pressed against the blue wing, and the wax will acquire the color of the butterfly. But when the surface of the wax is smoothed off the color disappears!
Truly, light blesses us with so many good things. Life itself is dependent upon the radiations from the sun that bathe our planet. But what a marvelous bonus we receive from light in its multitude of gorgeous colors! And whom should we thank for these blessings? Why, the Grand Creator, of course. Yes, thank “Jehovah, the Giver of the sun for light.”—Jer. 31:35.