the light source is the first important element of the observer situation. the statement has been made that without light thera is no color. Sir Isaac Newton conducted experiments with an optical prism and sunlight to confirm that white light is composed of spectral colors. the human response to color is limited to the visible spectrum of light, containing wavelengths between 380 and 770 nm. The wavelengths are associated with colors. beginning with violet at the short end of the spectrum. through indigo. blue, green, yellow, orange, and finally red at the long end. The nanometer is the accepted unit of length for light waves. the light is referred to as an illuminant when color is computed using data from a spectrophotometer.