This Design Guide is an introduction to most of the light sources used for general lighting. It provides lighting designers with essential information so that they can discriminate between the various characteristics of each source. This Guide also illustrates the typical shapes of commonly available lamps, and includes the corresponding American National Standards Institute (ANSI) designation used by lamp manufacturers. And lighting systems are identified by the type of lighting produced, while luminaires are divided into six classifications, based on specific light distribution characteristics. This Guide explains why selecting light sources, luminaires, controls, and system layouts involve closely interrelated choices. While a basic understanding of each lamp?s technical characteristics is important, this Guide identifies several other key factors to consider when selecting a light source. These include the direct cost of light, the quality of this light, the potential damage that inappropriate light/light levels may inflict on sensitive materials, and the caveats found in lamp manufacturer?s literature (e.g., the small print). Such factors often determine a given lighting system?s optimum reliability and safety.