Physical Phenomenon of Light

Physical phenomenon of light or visual perception is associated with the various wavelengths in the visible portion of the electromagnetic spectrum. As a sensation experienced by humans and some animals, perception of color is a complex neurophysiological process. The methods used for color specification today belong to a technique known as colorimetry and consist of accurate scientific measurements based on the wavelengths of three primary colors.
White light is composed of electromagnetic vibrations, the wavelengths of which are evenly distributed from 35 to 75 millionths of a centimeter (about 14 to 30 millionths of an inch). If the intensity of these vibrations is strong, the light is white; if the intensity is less, the light is grey; and if the intensity is zero, the light is nonexistent or black. Light composed of vibrations of a single wavelength in the visible spectrum differs qualitatively from light of another wavelength. This qualitative difference is perceived subjectively as hue. Light with a wavelength of 0.000075 cm (0.000030 in) is perceived as red, and light of 0.000035 cm (0.000014 in) wavelength is perceived as violet. The quality of the intermediate wavelengths is perceived as blue, green, yellow, or orange, moving from the wavelength of violet to that of red.
The color of light of a single wavelength or of a small band of wavelengths is known as a pure spectral color or hue. Such pure colors are said to be fully saturated and are seldom encountered outside the laboratory. An exception is the light of the sodium-vapor lamps used on some modern highways, which is almost fully saturated spectral yellow. The wide variety of colors seen every day are colors of lower saturation, that is, mixtures of light of various wavelengths. Hue and saturation are the two qualitative differences of physical colors. The quantitative difference is brilliance, the intensity or energy of the light.