Study Guide: Additive Light
Color perception, like sound perception, is a complex subject involving the disciplines of psychology, physiology, biology, chemistry and physics. When you look at an object and perceive a distinct color, you are not necessarily seeing a single frequency of light. Consider for instance that you are looking at a shirt and it appears purple to your eye. In such an instance, there may be several frequencies of light striking your eye with varying degrees of intensity. Yet your eye-brain system interprets the frequencies that strike your eye and the shirt is decoded by your brain as being purple.
Primary Colors of Light
The subject of color perception can be simplified if we think in terms of primary colors of light. We have already learned that white is not a color at all, but rather the presence of all the frequencies of visible light. When we speak of white light, we are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining the range of frequencies in the visible light spectrum is not the only means of producing white light. White light can also be produced by combining only three distinct frequencies of light, provided that they are widely separated on the visible light spectrum. Any three colors (or frequencies) of light that produce white light when combined with the correct intensity are called primary colors of light. There are a variety of sets of primary colors. The most common set of primary colors is red (R), green (G) and blue (B). When red, green and blue light are mixed or added together with the proper intensity, white (W) light is obtained. This is often represented by the equation below:
$$ R + G + B = W $$
In fact, the mixing together (or addition) of two or three of these three primary colors of light with varying degrees of intensity can produce a wide range of other colors. For this reason, many television sets and computer monitors produce the range of colors on the monitor by the use of red, green and blue light-emitting phosphors.
Visible Light
Visible light—that which is detectable by the human eye—consists of wavelengths ranging from approximately 780 nanometer ($7.80 \times 10-7 m$) down to 390 nanometer ($3.90 \times 10-7 m$). Specific wavelengths within the spectrum correspond to a specific color based upon how humans typically perceive light of that wavelength. Long wavelengths are perceived by humans as red and short wavelengths are perceived as violet. Other colors within the spectrum include orange, yellow, green and blue.
More Information
- The Physics Classroom: Color
- The Physics Classroom: Color Addition
- The Physics Classroom: Visible Light and the Eye
- The Physics Classroom: Additive Light Interactive