ABSTRACT
The high pressure mercury discharge was recognized as a possible source of light as early as 1906 by Kuch and Retachinsky, who made studies of the discharge. In the early 1950s, improved seals, emission materials and phosphors were developed for the high pressure mercury vapor lamp, which greatly increased lamp life, improved color and provided better lumen maintenance. The sodium radiation at low pressure consists of two narrow resonance lines at 589.0 and 589.6 nanometers. Mercury and sodium, when mixed together, form an amalgam in which the vapor pressure of each is less than it would be as separated elements. The high pressure sodium (HPS) lamp arc tubes evolved in their design with changes that reduced the sodium losses through the seal, improved the purity and consistency of the sodium amalgam dosage, improved the emission material, altered the design of the electrode and optimized the arc tube dimensions. HPS lamps are most generally used in outdoor lighting applications.
