Most streetlamps had been HID lamps for a long time: https://en.wikipedia.org/wiki/High-intensity_discharge_lamp https://en.wikipedia.org/wiki/High-intensity_d

Most streetlamps had been HID lamps for a long time: https://en.wikipedia.org/wiki/High-intensity_discharge_lamp https://en.wikipedia.org/wiki/High-intensity_discharge_lamp Efficiency was one reason for this, but the bigger reason was just that (for the duty cycle of a streetlamp) they require fewer installations and last way longer than incandescent bulbs. This means that the maintenance costs are much lower.