Vari-coloured street lamps

Here's a puzzler. Street lights tend to be of the old yellow sodium style, this applies to both the metal poled and the concrete poled versions that run along the Dunley Road. However some time ago the concrete set running from past the Rough towards Areley Common were replaced with higher metal posts the light emitted from these new heads can only be described as 'pinkish'.

Recently the set of concrete posts running in the other direction were also changed; the light these emit - white.

So we coming from the town we now have run white, pink, yellow. Do our council not specify the colour; do they just buy a job lot, have white heads become cheaper since they bought the pink heads?

I'm not complaining - the white heads are excellent and it's almost the equivalent of daytime driving now; but why are the pink ones still up?

[Update - another point is that the high-vis white lights occur when there are street lights on both sides of the road  whereas the lower intensity pink lights overlap a stretch when they exist on only one side]