Light That Swings Quick as a Mood.

Discusses light-emitting diodes, or L.E.D.'s. Use of L.E.D.'s in traffic lights in New York City in 2000; Increasing popularity in restaurants, Broadway shows, and atriums; Rapid progression of technology; Appeal for interior designers; Description of L.E.D.'s as semiconductors that convert electricity into single wavelengths of light; Life span of 30 to 40 years; generation of 50 percent more light than standard incandescent light sources; Production of virtually no heat; Potential to install them behind glass.