Let There Be Light!
- Monday, May 04, 2009
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Beginning in Genesis and going through Revelation, light is mentioned in the Bible more than one hundred times. “Let there be light” (Genesis 1:3), “Light of the world” (Matthew 5:14), and “I [Jesus] am the light of the world” (John 8:12, 9:5) are all from familiar verses of the Bible. In the Word of God, light is used to illustrate important points such as wisdom, illumination, and good vs. evil. But what is “light” from a scientist’s perspective?
From the ancient Greeks and Egyptians to Newton to Einstein to modern-day engineers, the quest to understand light and use it is rich with history. While this history is worthy of study in and of itself, this article will briefly touch on the fascinating science of light and color and describe a few inexpensive hands-on experiments that you can try at home.
What Is Light?
Like all other topics in science, knowledge builds upon knowledge. The ancient Greeks and Egyptians thought that light was something that emanated from our eyes. Today we know that light is a form of electromagnetic energy. Some light we can see; some we cannot. The light that we can see is called visible light. It is a small portion of the broad spectrum of electromagnetic radiation.
Light is unique in that it exhibits the properties of both a wave and a particle. If two people were holding a jump rope, and one of them snapped her wrist, the rope would move in “waves.” This motion gives us a good illustration of the way light travels in waves. That action adds energy to the rope in the form of a wave that travels along the length of the jump rope to the other person. Each time the jump rope holder snaps her wrist, another wave is generated.
The distance between one peak of the wave to the next peak is referred to as the wavelength. The wavelengths in the visible spectrum are measured in nanometers and range approximately from 380 to 740 nanometers. A nanometer is one-billionth of a meter. (A human hair is about 100,000 nanometers wide.)
The number of waves passing through our jump rope (or in a light wave) over a given time period is referred to as the frequency. Frequency is measured in cycles per second and the unit of measurement is a hertz. The higher the frequency is, the higher the energy in the wave.
In the visible part of the spectrum, color depends on the wavelength. The colors we can see range from dark red to deep violet and can be remembered by the fictitious man’s name: Roy G. Biv, which is a mnemonic for Red, Orange, Yellow, Green, Blue, Indigo, Violet. Of these, the primary colors are red, green, and blue (RGB).
All colors in the visible spectrum can be created by mixing different proportions of the three primary colors. This is the basis by which nature and our PCs, televisions, and other electronic display devices operate. Given this, what three wavelengths of color do you think our eyes are designed to be sensitive to? You guessed it: red, green, and blue. In fact, our eyes are most sensitive to yellow-green wavelengths. Is it any wonder why tennis balls and safety vests are this color?
But what about white? Isn’t it a color of light? Why isn’t it a part of the spectrum? Our eyes see white, but as Sir Isaac Newton (1643–1727) proved in 1665, the combination of all three primary colors of the spectrum actually produces white light. White is the presence of all colors, and black is the absence of all colors.
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