Recent developments in light sources

LIGHT is usually produced through the process of either incandescence (which for this general discussion may be taken to include combustion) or luminescence. Sources brought to a glowing temperature of incandescence are usually accompanied by infrared or heat radiation and very little ultraviolet radiation. Those that produce light through the process generally characterized as luminescence are electronic devices that may produce a good deal of ultraviolet as well as infrared radiation. Generally speaking, incandescent sources provide continuous spectra, whereas luminescent sources provide line or band spectra. Indications of several responses to radiation in the ultraviolet, visible, and infrared regions are set forth in Figure 1.