High Pressure Sodium Lighting

High Pressure Sodium (HPS) lamps are similar to Low Pressure Sodium fixtures in that they are both sodium vapor lamps. The difference though is that HPS lamps are smaller and contain additional elements like mercury that cause a dark pink glow when first struck and a magenta-orange color when fully warmed.

Due to the broad color range caused by the sodium’s high pressure within the lamp and the mercury emissions, the colors of object under these lamps can be easily distinguished. This stark contrast from low pressure sodium lighting leads them to be used in more desirable locations where color quality is important, either by design or necessity. Some examples of this would be accent flood lighting on the exterior of a building, gymnasium lighting or within a parking garage where security and footcandle levels are very important.

HPS lamps are very commonly used in the same applications as metal halide. Very often, electrical engineers/designers are presented with the decision of whether to specify the metal halide or high pressure sodium but this is a decision of personal preference. The decision is usually affected by personal experience, the cost at the time of the design and the owner’s maintenance preference.

High Pressure Sodium lamping is very energy efficient (100 lm/W) and they last approximately 20,000 hours. During the end of life of a HPS lamp it begins to “cycle”. This is a phenomenon where the loss of sodium requires the voltage to be increased in order to maintain the arc discharge. Eventually, the voltage required exceeds the ballast so modern ballasts won’t even attempt to start the lamp.

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

High Pressure Sodium Lamp 1