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3. Use of Colors

3.1 Historical Perspective on Color

While red, green, and blue are theoretically sufficient to produce any other color in the spectrum of visible light (Helmholtz three pigment color theory), there exists sufficient empirical evidence that supports separately adding yellow and white for improving the blending of colors (Hering three opponent color theory).

In the late 1800s, Hermann von Helmholtz and Ewald Hering have proposed two differing theories on human perception of color. Helmholtz suggested that there are three perceptors (red, green, and blue), which react and produce a sensation based on the wavelength of light. Hering on the other hand suggested that there are 3 processes in the eye or brain, equivalent to three pairs of opposing colors (red-green, blue-yellow, and white-black), which generate the perception of color. Scientist now understand that both of these theories are correct: The Helmholtz theory of three colors applies to the receptor level, and the Hering theory of opponent pairs applies to a subsequent stage of color perception and sensation in the visual path.

[ David Hubel, "Eye, Brain, Vision", Chapter 8, on-line book ]

3.2 Physical Perspective on Color

In particular for the LED Lamp, separate colors for yellow (red and green) do not blend well, as they are physically distinct diodes. The distance between the diodes and their projected light onto a surface is relatively short (< 20 feet) and thus the human eye is still able to differentiate between the component colors. Large LED video screens do not suffer from this phenomenon, because the diodes tend to be smaller, and their distance to the viewers (human eyes) tends to be much larger.

Besides the blending color problem, finer-grained spectra of colors beyond the 3 colors of red, green, and blue have already been used in domains such as color matching

[ A. Wenger, T. Hawkins, and P. Debevec: " Optimizing Color Matching in a Lighting Reproduction System for Complex Subject and Illuminant Spectra", Proceedings of the 14th Eurographics workshop on Rendering, Leuven, Belgium, 2003, pp. 249-259 ]