Hi there, asking here seams more apropriate then on reddit or quora, because people here know everything about lamps, lanterns and color

I was wondering, why did street lights became white

We already had white streetlights before (if I read that corecly) they were called Mercury Vapor
Then people decided that High pressure sodium and Low pressure sodium ones were better, not sure why did they decide that, but they did, so people had to adjust to yellow/orange color which in my opinion is better for night then white

and now, we are going back to white for some reason

I am not sure if energy efficiency is the reason because Low pressure sodium (SOX) is more efficient then LED and a lot more efficiency then Mercury Vapor but they are still changing them for white leds

If people want more efficiency, and think LED is more efficienct (if you see everything not just how much power it draws, but also how expensive its to replace and repair and how long it lasts, LED doesn't seam more efficienct (not in this throw away society when u have to replace the whole fixture just to get the light to work) its alr, but why did they change the color

we have amber leds: https://www.innolumis.com/projecten?lang=en

if they just changed SOX/SON to amer leds, they would still get more efficiency and we would still have yellowish light at night, hardly anyone would even notice (and people hate change (even if they say they don't), why force it appon them if change not needed)

What I don't understand is why did they go to orange light at night in the first place, if now we are ditching this in favour of white? Did they forgot the reason why we went to orange in the first place?

In short, the argument for cities to select cold (high color temperature) versions of LEDs was so called 'scotopic vision'. This is (mostly) a false idea that the eye at low light level is more sensitive to shorter wavelengths so with colder light sources the same lighting effect can be achieved with lower illumination level and lower power consumption. The effect is kinda marginal in fact, and cold light at low level looks plain ugly, no doubts. Was widely  used by dishonest LED salesmen a few years ago. Also, high color temperature LEDs are *slightly* more efficient, as more blue light is used directly instead of being downconverted by phosphor coating. Today, LED street lighting can be had in warm 3000K or slightly higher color temperature, and relatively high color rendering, which is the best light quality option compared to all historical street light sources, except may be incandescent lamps and gas mantles, though both were of course awfully inefficient...

I see, but why did we go from cold Mercury Vapor to warm LPS/HPS back in the day, I thought people knew about 'scotopic vision' even in the past

That is because HPS/LPS lamps are significantly more efficient (2-4 times!) than mercury lamps, so energy savings were very large! Even considering yellow light is slightly off the peak of the eye sensitivity.
   

Note that HPS lamps (at least in 250 and 400W versions) are still competitive with LEDs efficiency- and price-vise, and not yet banned in most of the countries because of this reason. Going to lower wattages in HPS lamps causes both efficiency and color quality to drop, so upgrading residential area lighting to proper LED lanterns (care to glare control, 3000K color temp) gives a *significant* light quality gain, plus energy saves, bringing green leaves back to green for example, which is immediately noticeable.

@veso266: HPS and LPS being replaced to LED because everyone saying that LED is the best energy saving choice and isn't contains toxic mercury (HPS contains mercury in the form of sodium-mercury amalgam, hence near EOL, the lamp turns red or pink and starting bluish mercury color).