Color Theory
Color
Thankfully, we live in a world with color. Because of color, we can appreciate life and beauty more fully. I believe that understanding why things have color allows me to appreciate color even more deeply. In this chapter, we will be discussing why most things have color. First, we need to take a quick look at some simple color theory. Then, we will learn what types of molecules are involved in giving most organic pigments their colors.
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Nature of light
A light wave can be described by its wavelength (λ) and frequency (ν).
Wavelength
Various Wavelengths of the light spectrum
The wavelength of the light is the distance between the peaks of the waves. This is a distance, so it is usually measured in a unit like meters or nanometers. Since all of these types of light travels at the speed of light, we could also count how many waves cross a point in one second. This count of the number of waves in one second is called the frequency. It is written as a #/second. Sometimes the unit is written as 1/s or s^-1 which is also called Hz (Hertz). Wavelength and frequency are inversely related to each other. The longer the wave, the fewer can pass by in one second, so the lower the frequency. The product of the wavelength and the frequency is equal to the speed of light, c. The speed of light in a vacuum is 3E8 m/s.
c = λν
The energy of a light wave is directly proportional to the frequency. The constant of proportionality is Planck’s constant (h = 6.63E-34Js). So, the higher the frequency of a light wave, the greater its energy is.
E = hν
Simple color theory
Sunlight is white light. It is a combination of all of the colors of the rainbow. We know this because the colors of white light can be separated if the sunlight passes through a prism or if it falls on a diffraction grating like a CD. So, when we are taking a hike along a trail and notice the colors of the beautiful flowers, we may wonder what gives them their color.
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Let’s say we are looking at a daisy. Obviously, the flower itself is not generating its own light. The light that is entering our eyes and allowing use to see the daisy originated in the sun. This white light that contains all colors, hit the daisy, bounced off of it, and into our eyes. White is a combination of all colors. When the sunlight hits the white petals of the daisy, all of the colors of the white sunlight bounce off of the petals and into your eyes. This rebounding of all colors from the white petals makes them look white to you. The yellow center of the daisy is a different story.
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The following, simplified color wheel roughly shows the colors of white light separated with the spectrum wrapped around so longest wavelength light, red, connect with the shortest wavelength light, violet. The color wheel is also arranged so that each color is directly opposite its complementary color.
For most things that have color, like the yellow center of the daisy, instead of all of the colors of light bouncing off of it, one of the colors is absorbed. It is absorbed because there is a chemical compound in it that absorbs one color. If one color from the white light is absorbed out of the white light, all of the other colors of the visible spectrum bounce off and enter your eye. This makes you see the complementary color of what is absorbed. For the yellow center of a daisy, there is a compound in it that absorbs light around 400-450 nm, which corresponds to blue/violet light. When blue/violet light is absorbed from the white light, the daisy center looks yellow to us. The compound that gives a tomato its red color absorbs light in the 440-500 nm range. This is an absorption in the blue and green part of the spectrum making the tomato their complementary color, red. Similarly, the compound responsible for giving blueberries their color absorbs around 530-600 nm of light, an orange color. The complementary color of the orange color that is absorbed from white light is the blue that we see. We will learn more about the compounds that absorb visible light in this chapter.
Absorbs 440-500 nm
Absorbs 530-600 nm
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