Low Pressure Sodium Lighting

Low Pressure Sodium (LPS) lighting is very commonly used in street lighting, security lighting and parking lot lighting. They are ideal for these types of locations due to the fact that the lamps last a very long time (5+ years) and color rendition is not an important factor in these locations.

A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. Low pressure sodium lamps, also known as sodium oxide lamps (SOX), consist of an outer vacuum envelope of glass coated with an infrared reflecting layer of a semiconductor material. The quality of light produced is mediocre at best but they are the most energy efficient man-made light source.

Initially, when the lamp is turned on it emits a dim pink-colored light to warm the sodium oxide metal and within a few minutes it changes to the common bright yellow as the sodium metal vaporizes. LPS lamps have a quick restrike unlike other HID lamps such as metal halide so that once switched on, there is not a long period of darkness.

During a LPS lamp’s life, the lamps start as a bright yellow glow but over time degrade to a dark orange. Unlike other bulbs that simply “burn out”, LPS lamps gradually decay during there life and even begin to increase energy usage towards the end of their life.

The average life of a low pressure sodium lamp is approximately 17,000 hours.

Below are samples of the most commonly used low pressure sodium lamps:

Low Pressure Sodium Lamp 1