The low pressure sodium lamp is regarded as the most efficient of all known lightsources. It has low running costs and long life time(about 18,000 hours). It is much used in street lights and is easily recognized by it's intense orange light. The fact that the light is monochromatic limits the use of this lightsource to applications where colour recognition isn't important

The LPS lamp consists of a arc tube made from sodium resistant glass. The tube is filled with a neon-argon mix and sodium. When the lamp is energized this gasmix starts ionizing. The heat from this procces vaporizes the sodium and starts to emit visible light. Outside the arc tube is another layer of glass. This is coated on the inside with heat reflective indium oxide, this keeps the heat inside the lamp so the sodium vaporizes faster. The LPS lamp often needs several minutes to reach the optimum operating temperature.