Color

Abstract

Two theories of color perception have been dominant. The trichromatic theory relates to blue‐, green‐, and red‐sensitive cones in the retina of the eye. It explains various forms of color blindness and is the basis of the CIE chromaticity diagram using x, y, Y . The opponent theory uses the opposites light/dark, red/green, and blue/yellow. It explains a variety of perception phenomena and is the basis of color spaces such as CIE L * a * b *. These apparently incompatible approaches apply to different parts of the color perception process. Modern electronic instruments have greatly simplified the measurement of color. Fifteen distinct chemical and physical mechanisms explain the various causes of color, all involving the behavior of electrons in matter. Vibrations and simple excitations explain the colors produced by incandescence (flames), gas excitation (vapor lamps), and vibrations and rotations (blue of water). Ligand field effects give the colors of transition‐metal compounds and impurities (turquoise and ruby, respectively). Molecular orbitals give the colors in organic compounds (dyes) and charge‐transfer compounds (blue sapphire). Energy bands lead to the colors of metals (copper), semiconductors (vermilion), doped semiconductors (blue diamond), and color centers (amethyst). Geometrical and physical optics explain colors from dispersive refraction (prism spectrum), scattering (blue sky), interference (soap bubble), and diffraction (opal).

The Effects of Trace Element Doping on the Optical Properties and Photocatalytic Activity of Nanostructured Titanium Dioxide

“…The illuminant was D65 (which represents daylight with a correlated color temperature of approximately 6500 K), and the field of view was 10°. The brightness and tone were calculated from X , Y , and Z values and were given L *, a *, and b * values according to the CIELAB system …”