Different designs and materials are needed to produce light in different parts of the electromagnetic spectrum . The following sections describe several different types of lamps that are useful in spectroscopy . A hot material, such as an electrically-heated filament in a light bulb, emits a continuum spectrum of light. Discharge Lamps Discharge lamps, such as neon signs, pass an electric current through a rare gas or metal vapor to produce light. The electrons collide with gas atoms, exciting them to higher energy levels which then decay to lower levels by emitting light.
Deuterium lamps are the uv source in uv-vis absorption spectrophotometers.
The sharp lines of the mercury and rare gas discharge lamps are useful for wavelength calibration of optical instrumentation. Mercury and xenon arc lamps are used to excite fluorescence. They get their name from the cup-shaped cathode, which is made from the element of interest. The electric discharge ionizes rare gas atoms, which are accelerated into the cathode and sputter metal atoms into the gas phase. Collisions with gas atoms or electrons excite the metal atoms to higher energy levels, which decay to lower levels by emitting light.