Location: Ch 4: Color
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Location: Ch 4: Color
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COLOR
IN THIS CHAPTER:
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hen we see color, what our eyes receive is several light waves with different
frequencies and amounts of energy. A red light has a low frequency and
a lower amount of energy, while a violet light is a higher energy wave
with a high frequency. White light is a combination of all colors. The
color of most objects is determined by which frequencies of light the object
reflects back. When a white light shines on a colored object, that object
absorbs some of the colors but reflects the rest. In one material, electrons
oscillate readily at certain frequencies. Any light with the same frequency
will be absorbed, and any other light will be reflected. For example, if
an object absorbs only green light, red and blue will both be reflected
and the object will appear to be cyan. However, an object may appear yellow
simply because there is no blue light. An object cannot reflect light that
is not present in the illuminating light. Therefore, a red shirt will appear
black in the presence of blue light.
Light waves of
different frequencies can be mixed together to produce another color. When
such a process happens, all the energy of the light waves is combined and
the resulting light has even more energy. This is known as the additive
nature of light. Sometimes two colors can be added together to produce
white. Adding colors is called color mixing by addition. When equal amounts
of complementary colors such as blue and yellow, magenta and green, or
cyan and red are combined, white light is produced. In any of these equations,
white is always produced because the amount of energy resulting from the
combinations is always the same. This is because all three equations are
essentially the same thing. Yellow is a combination of red and green, magenta
is a combination of red and blue, and cyan is a combination of blue and
green. Since the three equations all add red green and blue, the amounts
of energy combined are the same and therefore the result is always white.
If you subtract a color from white light, the result will be the complement
of the color you subtracted. For example, green’s complement is magenta.
However, a different procedure takes place with the mixing of colored paints, dyes and printer ink. This is known as the subtractive nature of light. Colored pigments work by reflecting only certain frequencies of light and absorbing the rest. Most of these pigments absorb and reflect a wide range of colors. Blue paint absorbs red, orange and yellow and reflects blue, violet and green. If blue and green paint are mixed, they absorb all colors except green. This is known as mixing colors by subtraction.
Energy also causes light to scatter in the atmosphere. When a light falls on an atom, the energy in the beam of light causes the electrons of the atom to temporarily move to a larger orbit. These electrons then emit the light energy in various directions, thus scattering the light. Light waves that have greater amounts of energy, such as blue and violet light, scatter easily in the atmosphere, and we see a blue sky. During a sunset, blue and violet light from the sun are scattered so much that all the energy in those light waves is completely scattered, and the sky turns red. Unlike the atmosphere, water does not get its blue-green color by scattering light. Water molecules resonate to red light and slowly absorb the red. Since red light is absorbed by water, we see its complementary color, cyan. Thus, the color of water is cyan.
In conclusion, the color of an object is due to the color light it reflects or transmits. Light is absorbed if its frequencies match the natural frequency of the electrons in the material being illuminated. White is a mix of all colors and black is the absence of light. Color mixing by addition is the combining of lights of different frequencies. The colors that can make the most combinations are red, green and blue. However, color subtraction is completely different. The paints or dyes absorb colors except for the ones that give them color. When colors are subtracted, magenta, cyan and yellow are the primary colors. When white sunlight travels through the atmosphere, blue light is scattered and enters our eyes, giving the sky the color blue. However, during sunsets, blue light is scattered until it disappears, leaving only red.