Spectral Colors

In a rainbow or the separation of colors by a prism we see the continuous range of spectral colors (the visible spectrum). A spectral color is composed of a single wavelength and can be correlated with wavelength as shown in the chart below ( a general guide and not a precise statement about color). It is safe enough to say that monochromatic light like the helium-neon laser is red (632 nm) or that the 3-2 transition from the hydrogen spectrum is red ( 656 nm) because they fall in the appropriate wavelength range. But most colored objects give off a range of wavelengths and the characterization of color is much more than the statement of wavelength. Perceived colors can be mapped on a chromaticity diagram.


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Vision concepts

Color vision

Visible spectrum
 
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Color

It is common practice to define pure colors in terms of the wavelengths of light as shown. This works well for spectral colors but it is found that manydifferent combinations of light wavelengths can produce the same perception of color.

This progression from left to right is from long wavelength to short wavelength, and from low frequency to high frequency light. The wavelengths are commonly expressed in nanometers (1 nm = 10-9 m). The visible spectrum is roughly from 700 nm (red end) to 400 nm (violet end). The letter I in the sequence above is for indigo - no longer commonly used as a color name. It is included above strictly for the reason of making the sequence easier to say as a mnemonic, like a person's name: Roy G. Biv - a tradition in the discussion of color.

The inherently distinguishable characteristics of color are hue, saturation, and brightness. Color measurement systems characterize colorsin various parameters which relate to hue, saturation, and brightness. They include the subjective Munsell and Ostwald systems and the quantitative CIE color system.

White light, or nearly white light from the Sun, contains a continuous distribution of wavelengths. The light from the Sun is essentially that of a blackbody radiator at 5780 K. The wavelengths (spectral colors) of white light can be separated by a dispersive medium like a prism. Even more effective separation can be achieved with a diffraction grating.

Index

Vision concepts

Color vision

Visible spectrum
 
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