The latest edition of “Inside Lighting Infoletter” web site  has an in depth article entitled” Investigating The Purple Light
Phenomenon In LED Street Lights”. Interesting conclusions.

Winnipeg got a call out and the pics look like the autobahn ATB0 that done turned blue in peg city
there was one on my route home I was watching slowly turn blue over a 1 year period and was 1/2 way transitioned when the supply failed and hydro in there usual have not done anything with it
last fall I happened to see it day burning and could look up at it running and see that the chips on the edge where blue with most of the ones in the centre of the assembly still white and it was an all or nothing on the chip part

This is so interesting my guess is extremely cheaply made Chinese chips. They wanted to capitalize on as much money as possible, and run away and hide. And of course people bought into it. No more pride like a made in America Westinghouse Lifeguard or Philips HPS down the road that’s been burning for 12 years. I have a brand new 250 W fixture that was put in when I moved into this house in 2011 and it is 100% the original bulb. I absolutely guarantee it as every single night. I check it. It’s turning more yellow, but it has never been out. it’s at the end of the street and I watched the facilities put the new cobra head up. Everything else in the area is LED except the light at the end of my block which I think is awesome but I’m sure as soon as it croaks they will put up an LED will better match everything but I will be sad as it’s been here since I’ve been here that very weak, I walked down and watched them screw the bulb! Apparently the one before completely quit. I was working on the house and noticed the light out and then the entire fixture was down and a brand new shiny gray fixture was put up. What a nice greeting to the neighborhood! Spring of 2011.