Light may be produced from electrical energy by exciting molecules with electrical energy.

The most common light sources are incandesent or ionic discharge tubes.

When a metal, usually tungsten, is heated by electrical energy to high temperatures, the metal glows, which is called incandescence. The incandescent lamps may be filled with bromine or iodine to allow the metal to be heated to higher temperatures which results in a whiter light. These lights are called halogen lamps. The color of the light from an incandescent lamp shifts with the temperature. Photographers select lighting by that temperature because color shifts with the temperature [local].

Electric discharge tubes produce light by exciting gaseous atoms in a tube with electric energy. Electrons in the molecules are excited to upper energy levels by the electric energy. When electrons return to the ground state, light is emitted in narrow bands of wavelengths. To produce a broader spectrum of light, the inside of the tube is coated with compounds that are fluorescent. Common fluorescent lights are filled with mercury and coated with a variety of compounds to produce different "colors" of light. Note that these three fluorescent lamps all emit the same mercury lines depicted by bars below, but the compounds coating the interior are different to shift the color.

However, discharge lamps may be filled with a variety of gases besides mercury to produce light of different wavelengths.

Two types of discharge lamps are common: arc and glow. Arc discharge lamps establish an electric arc between two electrodes. The gas in the tube is heated in this arc. Common fluorescent lights are arc discharge lamps. Glow discharge lamps do not establish an arc, but gases are excited by the flow of ions produced in the tube between the electrodes.

The quotes below are excerpts from a more complete review of light sources by David W. Ball at Cleveland State University.

"High-intensity and compact-arc lamps. High-intensity and compact-arc lamps produce the high brightness necessary for spectroscopic work. The gases are heated in the arc to the point that they are nearly the same temperature as the electrons (4000 to 10,000 K). The gaseous elements are excited by thermal processes in the electric arc. Although the emissions are characteristic of atomic spectra, the high pressures cause tremendous broadening of some lines (1 to 20 atm is typical; 100 atm is possible)."

"A general purpose UV/Vis source in this category is the xenon or xenon mercury lamp, which is available in wattages ranging from 50 W to several kilowatts. Another source in this category is the deuterium lamp. Although not as bright as Xe lamps and available only in rather low wattages (30 - 50 W), this lamp offers a continuum in the UV range and suffers less from the kind of intensity fluctuations found in Xe arc types." The deuterium lamp is frequently used in UV spectrophotometers.

"Hollow cathode lamps. Hollow cathode lamps (HCLs) are in the category of glow-discharge lamps because they do not achieve an arc. The lamp is principally used in atomic absorption (AA) spectroscopy where the material of the cathode matches the analyte. The elements in the cathode are sputtered into the discharge and emit line spectra. Any gases present (such as Ar and Ne) likewise emit. As power to the lamp increases, the bandwidth of the sputtered elements broadens, and analytical sensitivity reduces. The optimum current (or power) for AA is not necessarily the maximum current recommended by the manufacturer. For other applications, currents exceeding the recommended maximum may be acceptable. However, for many elements this maximum is related to lamp life. At excessive currents the cathode can melt or metal vapor can be flashed onto the front window."