HPS street lights rely on the sodium vapor to emit enough light, but at the beginning, the temperature is not enough for the solid sodium to vaporize. Instead, when the HPS street lights are just turned on, the mercury and xenon will emit light first. And their light is white. Later, when the temperature is high enough, sodium vapor starts to emit yellow light.
More reading: LED Street Lights VS HPS Street Lights: What’s Better in 2023?



