High pressure sodium (HPS) lamps, a member of the high intensity discharge (HID) lamp family, are the most efficient white light source commercially available today.  HPS lamps were developed and introduced in 1968 as energy-efficient sources for exterior, security, and industrial lighting applications, and are particularly prevalent in street lighting applications.  Due to their high efficiency and long life, today’s HPS lamps are also suitable for many interior applications, particularly where color rendering is not a crucial concern. 

High Pressure Sodium lamps, when compared to Low Pressure Sodium, are smaller and contain additional elements such as mercury.  They produce a dark pink glow when first struck and a pinkish orange light when warmed.  Some bulbs also briefly produce a pure to bluish white light in between.  This leads them to be used in areas where good color rendering is important, or desired.