Some Color Science Principles

Our perception of color results from many phenomena, including the nature of a light source and the effects of reflective surfaces on the light. An important distinction should be made before diving into color theory. Color reproduction can be accomplished by either additive or subtractive means.

Additive color, as we will see in the next section, is the addition of different colored lights to produce a variety of colors. Television uses additive color. Subtractive color, on the other hand, uses colorants (dyes or inks) that absorb some elements (frequencies) of light to reflect a derived color. Art paintings use subtractive color.

Spectral Light

In 1666, Sir Isaac Newton discovered that he could separate sunlight into a color spectrum by using a prism. He also found that he could recombine the color spectrum back into sunlight using a second inverted prism. Colors created from separating sunlight are called spectral colors.

Remember that a wave with a higher frequency and a shorter wavelength contains more energy than a wave with low frequency and long wavelengths. It is also true that a wave with a higher frequency bends more when light passes through a prism. As an example, the red light bends the least because it has a lower frequency.

In contrast, blue light has a high frequency and therefore bends the most. So, if you were looking at a rainbow, the red would bend the least and appears at the top. Blue light bends the most and appears at the bottom of rainbows.

Now you begin to understand the relationship between light and color. So far in this chapter, we have talked about how light is measured and have examined a color separation process. The next step in understanding the relationship between light and color is to classify how colors are created when different concentrations of light frequencies are used.

Because it is difficult, and usually unnecessary, to know the exact wavelength of a photon, the visible spectrum is divided into mutually exclusive and collectively exhaustive 10 nm bands. A source of light that generates all visible light frequencies in equal intensities within each band is called equi-energy white light and appears “white to the eye.” However, there is no unique, physical, or perceptual definition of “white light,” and many arbitrary light combinations are used as standards for different purposes.

Additive Color

Recall that an inverted prism recombines separated colors into an original light source. Here, light sources blend together to cause a different perceptual stimulation than the unblended light. Color computer display monitors approximate this process by placing different intensities of various primary colors (red, green, and blue) in close proximity, which our visual system subsequently blends to interpret as various colors.

Suppose now that you combined a red and blue light—the same as removing all green light from a separated equi-energy white light. Here, the resulting color sensation would be magenta—an example of non-spectral color. Nonspectral colors do not exist in the rainbow and are an artifact of the properties of the human visual system. The eye detects certain light frequencies and instructs the brain to construct a “close” color interpretation.

In the same way that removing green from an equi-energy light separation creates the illusion of magenta, the reverse is also true. Correct amounts of green (the missing color) and magenta (the perceptually invented color) combine to make white light. Colors that cause a white light sensation when mixed are called complementary colors.

If we removed all of the spectral colors except for a narrow part of the green area, then the green is called a fully saturated color. This means that the color is in its purest state, unsullied by other rainbow colors. If you begin to add in what appears to be magenta light, then the green light gradually becomes an unsaturated color or what is known as a pastel hue. Remember that magenta, in this case, is a complementary color to the green and that adding enough magenta eventually produces white. However, combining two fully saturated colors—in this case green and magenta—eventually produces a white light that may not be equi-energy white light. Passing this light through a prism may reveal that other spectral colors are missing.