![]() The Columbia Electronic Encyclopedia, 6th ed. The Quantum Explanation of Spectral Lines.The instrument used for studying line spectra is the spectroscope. Line spectra of either type are useful in chemical analysis, since they reveal the presence of particular elements. The Fraunhofer lines appearing in the spectrum of the sun are an example of a dark-line spectrum they are caused by the absorption of certain frequencies of light by the cooler, outer layers of the solar atmosphere. It consists of a series of dark lines superimposed on a continuous spectrum, each line corresponding to a frequency where a bright line would appear if the gas were incandescent. A dark-line, or absorption, spectrum is the reverse of a bright-line spectrum it is produced when white light containing all frequencies passes through a gas not hot enough to be incandescent. If the gas is made incandescent by heat or an electric discharge, the resulting spectrum is a bright-line, or emission, spectrum, consisting of a series of bright lines against a dark background. ![]() A gas under low pressure does not produce a continuous spectrum but instead produces a line spectrum, i.e., one composed of individual lines at specific frequencies characteristic of the gas, rather than a continuous band of all frequencies. Continuous spectra are produced by all incandescent solids and liquids and by gases under high pressure. The spectrum formed from white light contains all colors, or frequencies, and is known as a continuous spectrum. ![]() In addition to visible light, other types of electromagnetic radiation may be spread into a spectrum according to frequency or wavelength. Each different wavelength or frequency of visible light corresponds to a different color, so that the spectrum appears as a band of colors ranging from violet at the short-wavelength (high-frequency) end of the spectrum through indigo, blue, green, yellow, and orange, to red at the long-wavelength (low-frequency) end of the spectrum. Dispersion, the separation of visible light into a spectrum, may be accomplished by means of a prism or a diffraction grating.
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