A high-pressure sodium lamp (HPS) is a gas discharge lamp which emits light with natrium gas in an excited state. High Pressure Sodium lamps (SON / HPS) generally give light of a yellow-orange color, but each HPS type can color different. There are even HPS lamps that emit white light.
HPS lamps are mainly used in greenhouse/horticulture as assimilation lighting. The lamps are ideal to flourish plants, because of the high amounts of red light they emit. In addition, they are also frequently used as street lighting. The average light output is between 130 and 160 lumens / watt.