The different colors of the rainbow and the spectrum of colors produced by a prism illustrate one of light's fundamental characteristics: It exists in a virtually infinite number of shades. Each color is produced by an electromagnetic wave of a specific wavelength, frequency and energy. Visible light spans only a tiny sliver of the entire electromagnetic spectrum. Bluer colors have shorter wavelengths, higher frequencies and carry more energy. Redder colors have longer wavelengths, lower frequencies and carry less energy. The lower end of the spectrum ranges from radio waves that are hundreds of meters long, through millimeter-sized microwaves, to infrared radiation associated with radiant heat. The upper end proceeds from the ultraviolet rays that cause sunburn, through X-rays, up to gamma rays with wavelengths less than the diameter of an atom and energies three trillion times greater than typical radio waves.
Each color, or wavelength, interacts with matter in a different way. Radio waves push around free-flowing electrons, generating electrical signals in metal antennae. Microwaves cause the water molecules to vibrate inside solid food, producing the heat that cooks it. Ultraviolet radiation from the sun breaks down DNA. Different materials absorb and radiate light at different wavelengths. The patterns of absorption and radiation form universal signatures that allow scientists to identify the elemental composition of a material, whether it is in a laboratory on earth or surrounding a star in a distant
Contact: David F. Salisbury