Ray Fuller, age 11, of Winston Salem, N.C., for his question:
How can white light be made of colors?
Our eyes surpass the finest of man made cameras. Every waking moment they convey a multitude of moving pictures to the brain, and these images are captured both in color and in three dimensions. Animals also have vision, but so far as we know they do not see colors as we do.
When we see a vivid splash of color, our eyes are showing us some aspect of an invisible energy. For light is electromagnetic energy, and every color our eyes see is just one thread of this streaming energy. Light, of course, travels at roughly 186,000 miles a second. We know that several other travelers in the universe can equal its speed, but so far as we know nothing can surpass it. Most of our light is the daylight that spans the distance between the sun and us in about eight minutes.
The electromagnetic energy from the sun pulses along in wavelengths. Such wavelengths have been compared to the waves of the sea, and a single wavelength is the distance from one peak of energy to the next. The sun's energy is a blend of a vast variety of wavelengths ranging from infinitesimally small to very long. Altogether these various wavelengths are known as the electromagnetic spectrum. The rainbow spectrum of visible light is just a small section in this larger spectrum of energy.
Out in space, where there is no interference, the wavelengths of light are blended together we call this ordinary daylight white light, though actually it is invisible. It remains invisible until it strikes the atmosphere and the solid Earth. Then its different wavelengths are separated and split apart. Our eyes see these scattered wavelengths of white light as different colors.
When the shortest wavelengths of light are bent and scattered, we see them as deep purples and blues. They are bent and scattered by the small molecules of the gaseous air long before the daylight reaches the surface of the Earth. We look up and see the color of these short wave length rays spread over the sky.
The short wavelengths that our eyes see as blues are bent or refracted at sharp angles. The ones that are slightly longer are refracted less. Our eyes see them as the yellows and greens of the spectrum. The longest wavelengths are bent least. Our eyes see them as colored rays of orange and red.
The world around us is made up from a vast variety of substances and different surfaces. The different objects refract the blended wavelengths of white light in different ways. A red rose absorbs all except the longest wavelengths of light and reflects them back for our eyes to see as red. A purple pansy absorbs all the medium and long wavelengths and bounces the shortest waves back to our eyes.