Reddit mentions of Philips 321513 55-watt T15 SOX55 Low Pressure Sodium HID Light Bulb

Well, all that I know is readily available online, but the LPS wavelength spectrum is much more limited compared to HPS, so, as I understand it, it's much easier to filter out than HPS, let alone a LED.

Because of the above, LPS lamps render colors like this (the car to the left is red), so they are problematic when they are the only light source and colors have to be represented accurately - but cars already have their own lights, oftentimes LED, for that very purpose, while stores, apartment buildings and the like that may benefit from colors tend to feature their own lighting anyways.

As for the efficiency, compare a random 55-watt LPS bulb from 2004 to the superextramodernfeatured latest LED solutions from the same producer - if the sheets are to be believed, it turns out that, with all the problems LEDs present, they are only some 7% more efficient... And if they intelligently go darker at night, doesn't that just mean that the place either becomes less secure or simply didn't need that much light to begin with?

Neat website, either way! It might seem more trustworthy if it was possible to implement and enforce Let's Encrypt or some better SSL on it, as unfortunately we're going after emotions... :)

I built one for myself out of a sodium lamp and a ballast.

I am in a hurry right now, but I will come back later today with more info, some pictures and maybe even some drawings if I have them of what I made.