Low-pressure sodium lighting provides more energy-efficient outdoor lighting than high-intensity discharge lighting, but it has very poor color rendition. Typical applications include highway and security lighting, where color is not important.
Low-pressure sodium lamps work somewhat like fluorescent lamps. Like high-intensity discharge lighting, low-pressure sodium lamps require up to 10 minutes to start and have to cool before they can restart. Therefore, they are most suitable for applications in which they stay on for hours at a time. They are not suitable for use with motion detectors.
The chart below compares low-pressure sodium lamps and high-intensity discharge lamps.
|Color Rendition Index (CRI)||Color Temperature
|Mercury vapor||25–60||16,000–24,000||50 (poor to fair)||3200–7000 (warm to cold)||Outdoors|
|Metal halide||70–115||5000–20,000||70 (fair)||3700 (cold)||Indoors/outdoors|
|High-pressure sodium||50–140||16,000–24,000||25 (poor)||2100 (warm)||Outdoors|
|Low-Pressure Sodium||60–150||12,000–18,000||-44 (very poor)||Outdoors|