One of the more unique lamps in the lighting game: the low-pressure sodium vapor light
You will not find an impressive Color Rendering Index (CRI) or TLCI figure with these style lamps, but that is by design.
The low CRI/TLCI rating of 1 is not a flaw, but a feature because these lights are monochromatic.
The human eye is the most sensitive to yellow light, which is why these style of lamps still line most high-ways. Low-pressure sodium vapor lamps are commonly used along roadways, since its sodium glow doesn’t fatigue driver’s eyes.