LED efficiency was not impressive at all when streetlights first started using them but it has improved quite a lot and continues to improve. While being a lighting guy I hate to see the demise of discharge lighting and a great many unique light sources that have been developed over the years but whatever my opinions, LED is the future of lighting. At a lighting industry trade show last year literally *everything* being shown was LED. Other sources that had been popular, HID, fluorescent, induction, it was like they didn't exist at all. Low pressure sodium lamps are in the process of being phased out, I believe only one company still manufactures the lamps and production is likely to stop within a decade. Metal halide was promising, particularly the high color rendering ceramic types but development has pinnacled and essentially frozen as LED has surpassed the efficiency, lifespan and color quality. MH and HPS(SON) lamps are still made in large numbers as replacement lamps in existing luminaires but that will rapidly decrease. All new street lights that have been installed in my area within the last 5 years or so have been 100% LED, and very soon that is going to be all the major manufactures offer.
With LEDs being capable of instant-on, dimming, long life sealed luminaires that don't need relamping it's easy to see why they are taking over for roadway lighting. I think the sensor activated streetlights have merit if done properly, they could easily dim to say 10% power until movement is detected nearby. At 10% power a light will still appear much more than 10% of full brightness.
It's entirely possible to make LEDs that emit a nearly monochromatic yellow that mimics the color of low pressure sodium if the market desires. I've always thought LPS lamps looked cool but they never caught on in the US, I've only ever seen a very small handful of them in the wild.