Although they have similarities, light-emitting diodes (LEDs) and LDs have significant differences in their construction and application. LED systems are used for surface illumination, as a backlight in LCD TVs, and as indicators. The main purpose of LEDs in general lighting is the creation of a certain level of light and color on an illuminated surface. The power of conventional LED fixtures ranges from a few watts to several hundred watts. A LED system is usually simple and comprises only a single LED (or one or more LED strings) and a LED driver enclosed in the lighting fixture. Due to their relatively small power, LED systems usually use heatsinks to maintain an acceptable operating temperature, and they do not require forced cooling. Most LEDs have a single p-n junction. A white LED consists of a semiconductor structure that generates blue light and a phosphor coating that converts the blue light into white light. Practical Lighting Design with LEDs, by R. Lenk and C. Lenk, is an excellent source of information about modern LED characteristics and applications, as well as LED driver-circuit design.
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