Incandescent light is produced by electrically heating a resistive filament or the
burning of certain combustible materials. A large portion of the energy emitted
is in the infrared spectrum as well as the visible spectrum.
Atomic-type sources cover gas discharge devices such as neon and fluorescent
lights.
Laser emissions are obtained by excitation of the atoms of certain elements.
Semiconductor diodes (LED) are the most common commercially available
light sources used in industry. When forward biased, the diodes emit light in the
visible or IR region. Certain semiconductor diodes emit a narrow band of wavelength
of visible rays; the color is determined by material and doping. A list of
LEDs and their color is given in Table 10.1.