For here I think it started in 2016 if not 2015. That's when GEC started using LED for replacing yard lights or new ones, that I had noticed.

Duke seemed to start using LED in 2016 for new installations as well, and in a few instances for spot replacement, even though up until now they have been still installing HPS mostly for spot replacement. Lately LED seems to be popping up more and more and floodlights which were MH have now become LED.

DOT did a big changeout in our town on the highway to LED at some point in 2016 also. But the rest were left HPS and now have just been spot replaced, but most sections have at least one LED replacement at this point. There were a few new HPS installations in sections in 2017 even after the 2016 LED changeout.

2016-17 also had some new parking lots and commercial buildings having MH and fluorescent lighting. After that everything seemed to go LED for anything new.

So our area was a lot later than some to make the LED switch. I have heard of some areas having LED as late as 2007 and 2008 which 2007 I think is when Leotek made their first LED streetlights, which probably caused the rest of the manufacturers to follow.

It started out here around 2012/2013 when PG&E(?) started installing CREE LEDWay fixtures in some neighboring cities, Caltrans also installed some CREE LEDWay fixture around this time.

SVP Started using LEDs as early as 2014 but did not do a full change out until 2015 (full = all residential & commercial areas) industrial areas were left untouched except for spot replacements of dead (and sometimes working) HPS & MV fixtures.

2008, the first LED streetlights were installed on the new 35W bridge in Minneapolis. I was like 5 or 6 when they were put up and I thought they looked like robot heads. I have no idea who made them, but 12 years later they are still up. They are really dim but I think all of them still work.

https://www.google.com/maps/@44.9778635,-93.2456201,3a,15y,151.93h,111.56t/data=!3m6!1e1!3m4!1srndlTHLwA5jt5l_sXXqbkg!2e0!7i16384!8i8192

2008, the first LED streetlights were installed on the new 35W bridge in Minneapolis. I was like 5 or 6 when they were put up and I thought they looked like robot heads. I have no idea who made them, but 12 years later they are still up. They are really dim but I think all of them still work.

https://www.google.com/maps/@44.9778635,-93.2456201,3a,15y,151.93h,111.56t/data=!3m6!1e1!3m4!1srndlTHLwA5jt5l_sXXqbkg!2e0!7i16384!8i8192

Those look like RUUD "The Edge" fixtures (which later became CREE Edge after CREE bought RUUD), SFO airport also has some similar fixtures that are in the same shape.

Late 2010, I believe that's when the City of Vaughan first started changing out the HPS lights on the side and residential streets to LED. Ironically I think they still have HPS on most of the arterial streets.

Around 2012-2013, Caltrans replaced the HPS lights on the on and off ramps here.

In 2017, my city did a big LED conversion.

In 2014 first LED streetlights were mounted near my house.LEDs at that time were more expensive than now.

In our town the first LED streetlights appeared in 2010 as span wire version of the iGuzzini Argo LED. They replaced old lanterns with HWL 160W lamps.
In 2012 we installed the first pole mounted Stela Mini from Indal and later on Koffer2 LED.

August 2017 was when Ameren started using Leotek Green Cobras.  They just now (March 2020) started using the upgrade J series of GCJ, GCM, and GCL.  Other than efficiency, and more LEDs in the light engine, there really is no difference between those and the H series.  Surely in a couple of years, there will be an L series