HIGH-PRESSURE SODIUM - TEN YEARS LATER

The history of the development and utilization of high pressure sodium (HPS) lamps is presented, followed by a discussion on how HPS lamps operate and the present and future applications of HPS lamps. When compared with mercury systems, the HPS systems are found to have lower operating costs. They also emit more lumens per luminaire, which reduces the number of luminaires required for a given illumination level, compared to both mercury and fluorescent systems. Improvements are foreseen in the form of higher efficiency ballasting systems, better arc tube materials, and luminaires with improved light controlling characteristics.