A light-emitting diode is a semiconductor device that converts electrical energy into a discrete color of light. At the turn of the century, LEDs were used primarily for indication, as in, for example, clock radios; their use in lighting was still relatively new. An article in the December 2001 issue of Physics Today (page 42) described the rapid progress in LED development. Since that article was published, LEDs have continued to advance in all areas of performance and economics: Light output and quality, cost, use, and availability have all improved markedly. Now LEDs are beginning to be applied for general illumination. Moreover, the economics of energy and maintenance allow their use in many other ways—for example, as objects embedded into surfaces or structures. (See also Physics Today, Physics Today 0031-9228 60 12 2007 25 https://doi.org/10.1063/1.2825062 December 2007, page 25 .)
In addition to LED technology, the systems,...
