How Do High Pressure Sodium Lights Work?

Written by tyler lacoma
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How Do High Pressure Sodium Lights Work?
Sodium lights are used for public and security lighting. (car park light tower. image by mdb from

High pressure sodium lights are a specific type of light that creates an appreciated golden glow with only a fraction of the energy that other lights take. These lights have a variety of applications, and work due to the properties innate in the sodium gas. Low pressure lights take several minutes to charge up and to cool down before they can be turned on again, but high pressure lights respond more quickly.

Sodium Lights

Sodium lights function in a very similar method to fluorescent, mercury vapour, and metal halide lights. The primary difference between sodium lights and fluorescent lights is the absence of coatings in sodium lights. Fluorescent lights produce light by energising an inner coating on the bulb through the gas, while sodium lights actually energise the sodium gas trapped inside the bulb to produce the light.

Lighting Process

Sodium lights have an element inside the bulb that allows an electrical current to circulate through the light system. This current is carefully controlled by a ballast that reduces the voltages and current cycles to the proper levels. As this electricity passes through the gas, it gives some of its energy to the sodium atoms. The electrons of the atoms rise in energy levels, and as the current cycle passes they drop back again, releasing their excess energy in the form of light photons.

High Pressure and Low Pressure

The primary physical different between high pressure and low pressure sodium lights is the amount of gas used. Since high pressure gas lights contain more sodium gas, they tend to be brighter and produce a brighter, more golden glow. Low pressure lights take longer to start because they have fewer atoms to react to the electrical current, which in turn needs to build for a longer period before being channelled through the bulb.


High pressure sodium lights are very energy efficient, especially compared other high intensity discharge lighting options. This allows users to save money if they plan on having the lights on for long periods of time. High pressure sodium lights have low colour rendition index, which limits their application to areas where colour in lighting is not important.


High pressure sodium lights are used in construction and public lighting where lights are kept on for long periods of time. Car park lights, roadway lights and security lights all use sodium gas. Sodium lights are also very popular in the field of hydroponics, where the light range of sodium lights falls within the acceptable wavelengths for plants to live on.

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